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Risk/Return:

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Supplement to Prospectus [Text Block]

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Supplement dated June 21, 2023 to the Prospectus and Summary Prospectus, each dated February 1,

2023, as may be revised or supplemented from time to time, for the following fund:

LOOMIS SAYLES GLOBAL ALLOCATION FUND

LOOMIS SAYLES GROWTH FUND

(each, a “Fund”)

LOOMIS SAYLES GLOBAL ALLOCATION FUND

Effective July 1, 2023, Loomis, Sayles & Company, L.P. has given a binding contractual undertaking to the Fund to limit the amount of the Fund’s total annual fund operating expenses to 1.20%, 1.95%, 0.90%, 1.20% and 0.95% of the Fund’s average daily net assets for Class A, C, N, T and Y shares, respectively, exclusive of brokerage expenses, interest expense, taxes, acquired fund fees and expenses, organizational and extraordinary expenses, such as litigation and indemnification expenses. This undertaking is in effect through January 31, 2025.

Accordingly, the Annual Fund Operating Expenses table and the Example table within the section “Fund Fees & Expenses” are amended and restated as follows with respect to the Fund:

Annual Fund Operating Expenses

(expenses that you pay each year as a percentage of the value of your investment)


	Class A			Class C			Class N			Class T			Class Y
Management fees		0.74	%		0.74	%		0.74	%		0.74	%		0.74	%
Distribution and/or service (12b‑1) fees		0.25	%		1.00	%		0.00	%		0.25	%		0.00	%
Other expenses¹		0.15	%		0.15	%		0.07	%		0.15	%		0.15	%
Total annual fund operating expenses		1.14	%		1.89	%		0.81	%		1.14	%		0.89	%
Fee waiver and/or expense reimbursement²		0.00	%		0.00	%		0.00	%		0.00	%		0.00	%
Total annual fund operating expenses after fee waiver and/or expense reimbursement		1.14	%		1.89	%		0.81	%		1.14	%		0.89	%

¹	Other expenses for Class T shares are estimated for the current fiscal year.

Loomis, Sayles & Company, L.P. (“Loomis Sayles” or the “Adviser”) has given a binding contractual undertaking to the Fund to limit the amount of the Fund’s total annual fund operating expenses to 1.20%, 1.95%, 0.90%, 1.20% and 0.95% of the Fund’s average daily net assets for Class A, C, N T and Y shares, respectively, exclusive of brokerage expenses, interest expense, taxes, acquired fund fees and expenses, organizational and extraordinary expenses, such as litigation and indemnification expenses. This undertaking is in effect through January 31, 2025 and may be terminated before then only with the consent of the Fund’s Board of Trustees. The Adviser will be permitted to recover, on a class by class basis, management fees waived and/or expenses reimbursed to the extent that expenses in later periods fall below both (1) the class’ applicable expense limitation. The Fund will not be obligated to repay any such waived/reimbursed fees and expenses more than one year after the end of the fiscal year in which the fees or expenses were waived/reimbursed.

Example

This example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods (except where indicated). The example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses remain the same. The example for Class C shares for the ten‑year period reflects the conversion to Class A shares after eight years. The example does not take into account brokerage commissions and other fees to financial intermediaries that you may pay on your purchases and sales of shares of the Fund. Although your actual costs may be higher or lower, based on these assumptions your costs would be:


If shares are redeemed:	1 year		3 years		5 years		10 years
Class A	$	685	$	916	$	1,167	$	1,881
Class C	$	292	$	594	$	1,021	$	2,016
Class N	$	83	$	259	$	450	$	1,002
Class T	$	363	$	603	$	862	$	1,601
Class Y	$	91	$	284	$	493	$	1,096


If shares are not redeemed:	1 year		3 years		5 years		10 years
Class C	$	192	$	594	$	1,021	$	2,016

LOOMIS SAYLES GROWTH FUND

Effective July 1, 2023, Loomis, Sayles & Company, L.P. has given a binding contractual undertaking to the Fund to limit the amount of the Fund’s total annual fund operating expenses to 1.00%, 1.75%, 0.70%, 1.00% and 0.75% of the Fund’s average daily net assets for Class A, C, N, T and Y shares, respectively, exclusive of brokerage expenses, interest expense, taxes, acquired fund fees and expenses, organizational and extraordinary expenses, such as litigation and indemnification expenses. In addition, Loomis Sayles will waive its management fee on any portion of the Fund’s assets that are invested in the Natixis Loomis Sayles Focused Growth ETF. This undertaking is in effect through January 31, 2025.

Accordingly, the Annual Fund Operating Expenses table and the Example table within the section “Fund Fees & Expenses” are amended and restated as follows with respect to the Fund:

Annual Fund Operating Expenses

(expenses that you pay each year as a percentage of the value of your investment)


	Class A			Class C			Class N			Class T			Class Y
Management fees		0.50	%		0.50	%		0.50	%		0.50	%		0.50	%
Distribution and/or service (12b‑1) fees		0.25	%		1.00	%		0.00	%		0.25	%		0.00	%
Other expenses		0.15	%		0.15	%		0.07	%		0.15	%¹		0.15	%
Total annual fund operating expenses		0.90	%		1.65	%		0.57	%		0.90	%		0.65	%
Fee waiver and/or expense reimbursement²		0.00	%		0.00	%		0.00	%		0.00	%		0.00	%
Total annual fund operating expenses after fee waiver and/or expense reimbursement		0.90	%		1.65	%		0.57	%		0.90	%		0.65	%

¹	Other expenses for Class T shares are estimated for the current fiscal year.

Loomis, Sayles & Company, L.P. (“Loomis Sayles” or the “Adviser”) has given a binding contractual undertaking to the Fund to limit the amount of the Fund’s total annual fund operating expenses to 1.00%, 1.75%, 0.70%, 1.00% and 0.75% of the Fund’s average daily net assets for Class A, C, N T and Y shares, respectively, exclusive of brokerage expenses, interest expense, taxes, acquired fund fees and expenses, organizational and extraordinary expenses, such as litigation and indemnification expenses. In addition, Loomis Sayles will waive its management fee on any portion of the Fund’s assets that are invested in the Natixis Loomis Sayles Focused Growth ETF. This undertaking is in effect through January 31, 2025 and may be terminated before then only with the consent of the Fund’s Board of Trustees. The Adviser will be permitted to recover, on a class by class basis, management fees waived and/or expenses reimbursed to the extent that expenses in later periods fall below both (1) the class’ applicable expense limitation. The Fund will not be obligated to repay any such waived/reimbursed fees and expenses more than one year after the end of the fiscal year in which the fees or expenses were waived/reimbursed.

Example


If shares are redeemed:	1 year		3 years		5 years		10 years
Class A	$	662	$	845	$	1,045	$	1,619
Class C	$	268	$	520	$	897	$	1,754
Class N	$	58	$	183	$	318	$	714
Class T	$	340	$	530	$	736	$	1,330
Class Y	$	66	$	208	$	362	$	810


If shares are not redeemed:	1 year		3 years		5 years		10 years
Class C	$	168	$	520	$	897	$	1,754

Supplement dated June 21, 2023 to the Prospectus and Summary Prospectus, each dated February 1,

2023, as may be revised or supplemented from time to time, for the following fund:

LOOMIS SAYLES SMALL CAP GROWTH FUND

(each, a “Fund”)

LOOMIS SAYLES SMALL CAP GROWTH FUND

Effective July 1, 2023, Loomis, Sayles & Company, L.P. has given a binding contractual undertaking to the Fund to limit the amount of the Fund’s total annual fund operating expenses to 0.95%, 1.20% and 0.90% of the Fund’s average daily net assets for Institutional Class, Retail Class and Class N shares, respectively, exclusive of brokerage expenses, interest expense, taxes, acquired fund fees and expenses, organizational and extraordinary expenses, such as litigation and indemnification expenses. This undertaking is in effect through January 31, 2025.

Accordingly, the Annual Fund Operating Expenses table and the Example table within the section “Fund Fees & Expenses” are amended and restated as follows with respect to the Fund:

Annual Fund Operating Expenses

(expenses that you pay each year as a percentage of the value of your investment)


	Institutional Class			Retail Class			Class N
Management fees		0.75	%		0.75	%		0.75	%
Distribution and/or service (12b‑1) fees		0.00	%		0.25	%		0.00	%
Other expenses		0.18	%		0.18	%		0.07	%
Total annual fund operating expenses		0.93	%		1.18	%		0.82	%
Fee waiver and/or expense reimbursement¹		0.00	%		0.00	%		0.00	%
Total annual fund operating expenses after fee waiver and/or expense reimbursement		0.93	%		1.18	%		0.82	%

Loomis, Sayles & Company, L.P. (“Loomis Sayles” or the “Adviser”) has given a binding contractual undertaking to the Fund to limit the amount of the Fund’s total annual fund operating expenses to 0.95%, 1.20% and 0.90% of the Fund’s average daily net assets for Institutional Class, Retail Class and Class N shares, respectively, exclusive of brokerage expenses, interest expense, taxes, acquired fund fees and expenses, organizational and extraordinary expenses, such as litigation and indemnification expenses. This undertaking is in effect through January 31, 2025 and may be terminated before then only with the consent of the Fund’s Board of Trustees. The Adviser will be permitted to recover, on a class by class basis, management fees waived and/or expenses reimbursed to the extent that expenses in later periods fall below both (1) the class’ applicable expense limitation. The Fund will not be obligated to repay any such waived/reimbursed fees and expenses more than one year after the end of the fiscal year in which the fees or expenses were waived/reimbursed.

Example

The example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses remain the same. The example does not take into account brokerage commissions and other fees to financial intermediaries that you may pay on your purchases and sales of shares of the Fund. Although your actual costs may be higher or lower, based on these assumptions your costs would be:


	1 year		3 years		5 years		10 years
Institutional Class	$	95	$	296	$	515	$	1,143
Retail Class	$	120	$	375	$	649	$	1,432
Class N	$	84	$	262	$	455	$	1,014

Supplement dated June 21, 2023 to the Prospectus and Summary Prospectus, each dated May 1, 2023, as

may be revised or supplemented from time to time, for the following fund:

LOOMIS SAYLES HIGH INCOME FUND

LOOMIS SAYLES STRATEGIC INCOME FUND

(each, a “Fund”)

LOOMIS SAYLES HIGH INCOME FUND

Effective July 1, 2023, Loomis, Sayles & Company, L.P. has given a binding contractual undertaking to the Fund to limit the amount of the Fund’s total annual fund operating expenses to 0.95%, 1.70%, 0.65%, 0.95% and 0.70% of the Fund’s average daily net assets for Class A, C, N, T and Y shares, respectively, exclusive of brokerage expenses, interest expense, taxes, acquired fund fees and expenses, organizational and extraordinary expenses, such as litigation and indemnification expenses. This undertaking is in effect through April 30, 2025.

Accordingly, the Annual Fund Operating Expenses table and the Example table within the section “Fund Fees & Expenses” are amended and restated as follows with respect to the Fund:

Annual Fund Operating Expenses

(expenses that you pay each year as a percentage of the value of your investment)


	Class A			Class C			Class N			Class T			Class Y
Management fees¹		0.55	%		0.55	%		0.55	%		0.55	%		0.55	%
Distribution and/or service (12b‑1) fees		0.25	%		1.00	%		0.00	%		0.25	%		0.00	%
Other expenses²		0.34	%		0.34	%		1.21	%		0.34	%³		0.34	%
Total annual fund operating expenses		1.14	%		1.89	%		1.76	%		1.14	%		0.89	%
Fee waiver and/or expense reimbursement^4,5		0.18	%		0.18	%		1.10	%		0.18	%		0.18	%
Total annual fund operating expenses after fee waiver and/or expense reimbursement		0.96	%		1.71	%		0.66	%		0.96	%		0.71	%

¹	The Fund’s operating expenses have been restated to reflect a reduction in management fees, effective as of July 1, 2023, as if reduction had been in effect during the fiscal year ended December 31, 2022. The information has been restated to better reflect anticipated expenses of the Fund.

The expense information shown in the table above includes acquired fund fees and expenses of less than 0.01%; the ratios differ from the expense information disclosed in the Fund’s financial highlights table because the financial highlights table reflects the operating expenses of the Fund and does not include acquired fund fees and expenses.

³	Other expenses for Class T shares are estimated for the current fiscal year.

⁴

Loomis, Sayles & Company, L.P. (“Loomis Sayles” or the “Adviser”) has given a binding contractual undertaking to the Fund to limit the amount of the Fund’s total annual fund operating expenses to 0.95%, 1.70%, 0.65%, 0.95% and 0.70% of the Fund’s average daily net assets for Class A, C, N, T and Y shares, respectively, exclusive of brokerage expenses, interest expense, taxes, acquired fund fees and expenses, organizational and extraordinary expenses, such as litigation and indemnification expenses. This undertaking is in effect through April 30, 2025 and may be terminated before then only with the consent of the Fund’s Board of Trustees. The Adviser will be permitted to recover, on a class by class basis, management fees waived and/or expenses reimbursed to the extent that expenses in later periods fall below both (1) the class’ applicable expense limitation. The Fund will not be obligated to repay any such waived/reimbursed fees and expenses more than one year after the end of the fiscal year in which the fees or expenses were waived/reimbursed.

⁵

Natixis Advisors, LLC (“Natixis Advisors”) has given a binding contractual undertaking to the Fund to reimburse any and all transfer agency expenses for Class N shares. This undertaking is in effect through April 30, 2024 and may be terminated before then only with the consent of the Fund’s Board of Trustees.

Example

This example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods (except where indicated). The example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses remain the same, except that the example is based on the Total Annual Fund Operating Expenses After Fee Waiver and/or Expense Reimbursement assuming that such waiver and/or reimbursement will only be in place through the dates noted above and on the Total Annual Fund Operating Expenses for the remaining periods. The example for Class C shares for the ten‑year period reflects the conversion to Class A shares after eight years. The example does not take into account brokerage commissions and other fees to financial intermediaries that you may pay on your purchases and sales of shares of the Fund. Although your actual costs may be higher or lower, based on these assumptions your costs would be:


If shares are redeemed:	1 year		3 years		5 years		10 years
Class A	$	519	$	740	$	995	$	1,723
Class C	$	274	$	561	$	990	$	1,988
Class N	$	67	$	351	$	759	$	1,900
Class T	$	345	$	570	$	830	$	1,572
Class Y	$	73	$	250	$	460	$	1,065


If shares are not redeemed:	1 year		3 years		5 years		10 years
Class C	$	174	$	561	$	990	$	1,988

LOOMIS SAYLES STRATEGIC INCOME FUND

Effective July 1, 2023, Loomis, Sayles & Company, L.P. has given a binding contractual undertaking to the Fund to limit the amount of the Fund’s total annual fund operating expenses to 0.93%, 1.68%, 0.63%, 0.93%, 0.68% and 1.18% of the Fund’s average daily net assets for Class A, C, N, T, Y and Admin Class shares, respectively, exclusive of brokerage expenses, interest expense, taxes, acquired fund fees and expenses, organizational and extraordinary expenses, such as litigation and indemnification expenses. This undertaking is in effect through April 30, 2025.

Accordingly, the Annual Fund Operating Expenses table and the Example table within the section “Fund Fees & Expenses” are amended and restated as follows with respect to the Fund:

Annual Fund Operating Expenses

(expenses that you pay each year as a percentage of the value of your investment)


	Class A			Class C			Class N			Class T			Class Y			Admin Class
Management fees¹		0.57	%		0.57	%		0.57	%		0.57	%		0.57	%		0.57	%
Distribution and/or service (12b‑1) fees		0.25	%		1.00	%		0.00	%		0.25	%		0.00	%		0.25	%
Other expenses²		0.15	%		0.15	%		0.06	%		0.15	%³		0.15	%		0.40	%⁴
Total annual fund operating expenses		0.97	%		1.72	%		0.63	%		0.97	%		0.72	%		1.22	%
Fee waiver and/or expense reimbursement⁵		0.04	%		0.04	%		0.00	%		0.04	%		0.04	%		0.04	%
Total annual fund operating expenses after fee waiver and/or expense reimbursement		0.93	%		1.68	%		0.63	%		0.93	%		0.68	%		1.18	%

¹	The Fund’s operating expenses have been restated to reflect a reduction in management fees, effective as of July 1, 2023, as if reduction had been in effect during the fiscal year ended December 31, 2022. The information has been restated to better reflect anticipated expenses of the Fund.

²	Other expenses include acquired fund fees and expenses of less than 0.01%.

³	Other expenses for Class T shares are estimated for the current fiscal year.

⁴	Other expenses include an administrative service fee of 0.25% for Admin Class shares.

⁵

Loomis, Sayles & Company, L.P. (“Loomis Sayles” or the “Adviser”) has given a binding contractual undertaking to the Fund to limit the amount of the Fund’s total annual fund operating expenses to 0.93%, 1.68%, 0.63%, 0.93%, 0.68% and 1.18% of the Fund’s average daily net assets for Class A, C, N, T, Y and Admin Class shares, respectively, exclusive of brokerage expenses, interest expense, taxes, acquired fund fees and expenses, organizational and extraordinary expenses, such as litigation and indemnification expenses. This undertaking is in effect through April 30, 2025 and may be terminated before then only with the consent of the Fund’s Board of Trustees. The Adviser will be permitted to recover, on a class by class basis, management fees waived and/or expenses reimbursed to the extent that expenses in later periods fall below both (1) the class’ applicable expense limitation. The Fund will not be obligated to repay any such waived/reimbursed fees and expenses more than one year after the end of the fiscal year in which the fees or expenses were waived/reimbursed.

Example

This example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods (except where indicated). The example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses remain the same, except that the examples for Class A, C, T, Y and Admin Class are based on the Total Annual Fund Operating Expenses After Fee Waiver and/or Expense Reimbursement assuming that such waiver and/or reimbursement will only be in place through the dates noted above and on the Total Annual Fund Operating Expenses for the remaining periods. The example for Class C shares for the ten‑year period reflects the conversion to Class A shares after eight years. The example does not take into account brokerage commissions and other fees to financial intermediaries that you may pay on your purchases and sales of shares of the Fund. Although your actual costs may be higher or lower, based on these assumptions your costs would be:


If shares are redeemed:	1 year		3 years		5 years		10 years
Class A	$	516	$	714	$	931	$	1,558
Class C	$	271	$	535	$	926	$	1,825
Class N	$	64	$	202	$	351	$	786
Class T	$	343	$	544	$	766	$	1,403
Class Y	$	69	$	223	$	393	$	887
Admin Class	$	120	$	380	$	663	$	1,471


If shares are not redeemed:	1 year		3 years		5 years		10 years
Class C	$	171	$	535	$	926	$	1,825

Loomis Sayles Global Allocation Fund

Risk/Return:

rr_RiskReturnAbstract

Supplement to Prospectus [Text Block]

rr_SupplementToProspectusTextBlock

Supplement dated June 21, 2023 to the Prospectus and Summary Prospectus, each dated February 1,

2023, as may be revised or supplemented from time to time, for the following fund:

LOOMIS SAYLES GLOBAL ALLOCATION FUND

(each, a “Fund”)

LOOMIS SAYLES GLOBAL ALLOCATION FUND

Accordingly, the Annual Fund Operating Expenses table and the Example table within the section “Fund Fees & Expenses” are amended and restated as follows with respect to the Fund:

Annual Fund Operating Expenses

(expenses that you pay each year as a percentage of the value of your investment)


	Class A			Class C			Class N			Class T			Class Y
Management fees		0.74	%		0.74	%		0.74	%		0.74	%		0.74	%
Distribution and/or service (12b‑1) fees		0.25	%		1.00	%		0.00	%		0.25	%		0.00	%
Other expenses¹		0.15	%		0.15	%		0.07	%		0.15	%		0.15	%
Total annual fund operating expenses		1.14	%		1.89	%		0.81	%		1.14	%		0.89	%
Fee waiver and/or expense reimbursement²		0.00	%		0.00	%		0.00	%		0.00	%		0.00	%
Total annual fund operating expenses after fee waiver and/or expense reimbursement		1.14	%		1.89	%		0.81	%		1.14	%		0.89	%

¹	Other expenses for Class T shares are estimated for the current fiscal year.

Example


If shares are redeemed:	1 year		3 years		5 years		10 years
Class A	$	685	$	916	$	1,167	$	1,881
Class C	$	292	$	594	$	1,021	$	2,016
Class N	$	83	$	259	$	450	$	1,002
Class T	$	363	$	603	$	862	$	1,601
Class Y	$	91	$	284	$	493	$	1,096


If shares are not redeemed:	1 year		3 years		5 years		10 years
Class C	$	192	$	594	$	1,021	$	2,016

Loomis Sayles Growth Fund

Risk/Return:

rr_RiskReturnAbstract

Supplement to Prospectus [Text Block]

rr_SupplementToProspectusTextBlock

Supplement dated June 21, 2023 to the Prospectus and Summary Prospectus, each dated February 1,

2023, as may be revised or supplemented from time to time, for the following fund:

LOOMIS SAYLES GROWTH FUND

(each, a “Fund”)

LOOMIS SAYLES GROWTH FUND

Effective July 1, 2023, Loomis, Sayles & Company, L.P. has given a binding contractual undertaking to the Fund to limit the amount of the Fund’s total annual fund operating expenses to 1.00%, 1.75%, 0.70%, 1.00% and 0.75% of the Fund’s average daily net assets for Class A, C, N, T and Y shares, respectively, exclusive of brokerage expenses, interest expense, taxes, acquired fund fees and expenses, organizational and extraordinary expenses, such as litigation and indemnification expenses. In addition, Loomis Sayles will waive its management fee on any portion of the Fund’s assets that are invested in the Natixis Loomis Sayles Focused Growth ETF. This undertaking is in effect through January 31, 2025.

Accordingly, the Annual Fund Operating Expenses table and the Example table within the section “Fund Fees & Expenses” are amended and restated as follows with respect to the Fund:

Annual Fund Operating Expenses

(expenses that you pay each year as a percentage of the value of your investment)


	Class A			Class C			Class N			Class T			Class Y
Management fees		0.50	%		0.50	%		0.50	%		0.50	%		0.50	%
Distribution and/or service (12b‑1) fees		0.25	%		1.00	%		0.00	%		0.25	%		0.00	%
Other expenses		0.15	%		0.15	%		0.07	%		0.15	%¹		0.15	%
Total annual fund operating expenses		0.90	%		1.65	%		0.57	%		0.90	%		0.65	%
Fee waiver and/or expense reimbursement²		0.00	%		0.00	%		0.00	%		0.00	%		0.00	%
Total annual fund operating expenses after fee waiver and/or expense reimbursement		0.90	%		1.65	%		0.57	%		0.90	%		0.65	%

¹	Other expenses for Class T shares are estimated for the current fiscal year.

Loomis, Sayles & Company, L.P. (“Loomis Sayles” or the “Adviser”) has given a binding contractual undertaking to the Fund to limit the amount of the Fund’s total annual fund operating expenses to 1.00%, 1.75%, 0.70%, 1.00% and 0.75% of the Fund’s average daily net assets for Class A, C, N T and Y shares, respectively, exclusive of brokerage expenses, interest expense, taxes, acquired fund fees and expenses, organizational and extraordinary expenses, such as litigation and indemnification expenses. In addition, Loomis Sayles will waive its management fee on any portion of the Fund’s assets that are invested in the Natixis Loomis Sayles Focused Growth ETF. This undertaking is in effect through January 31, 2025 and may be terminated before then only with the consent of the Fund’s Board of Trustees. The Adviser will be permitted to recover, on a class by class basis, management fees waived and/or expenses reimbursed to the extent that expenses in later periods fall below both (1) the class’ applicable expense limitation. The Fund will not be obligated to repay any such waived/reimbursed fees and expenses more than one year after the end of the fiscal year in which the fees or expenses were waived/reimbursed.

Example


If shares are redeemed:	1 year		3 years		5 years		10 years
Class A	$	662	$	845	$	1,045	$	1,619
Class C	$	268	$	520	$	897	$	1,754
Class N	$	58	$	183	$	318	$	714
Class T	$	340	$	530	$	736	$	1,330
Class Y	$	66	$	208	$	362	$	810


If shares are not redeemed:	1 year		3 years		5 years		10 years
Class C	$	168	$	520	$	897	$	1,754

Loomis Sayles Small Cap Growth Fund

Risk/Return:

rr_RiskReturnAbstract

Supplement to Prospectus [Text Block]

rr_SupplementToProspectusTextBlock

Supplement dated June 21, 2023 to the Prospectus and Summary Prospectus, each dated February 1,

2023, as may be revised or supplemented from time to time, for the following fund:

LOOMIS SAYLES SMALL CAP GROWTH FUND

(each, a “Fund”)

LOOMIS SAYLES SMALL CAP GROWTH FUND

Effective July 1, 2023, Loomis, Sayles & Company, L.P. has given a binding contractual undertaking to the Fund to limit the amount of the Fund’s total annual fund operating expenses to 0.95%, 1.20% and 0.90% of the Fund’s average daily net assets for Institutional Class, Retail Class and Class N shares, respectively, exclusive of brokerage expenses, interest expense, taxes, acquired fund fees and expenses, organizational and extraordinary expenses, such as litigation and indemnification expenses. This undertaking is in effect through January 31, 2025.

Accordingly, the Annual Fund Operating Expenses table and the Example table within the section “Fund Fees & Expenses” are amended and restated as follows with respect to the Fund:

Annual Fund Operating Expenses

(expenses that you pay each year as a percentage of the value of your investment)


	Institutional Class			Retail Class			Class N
Management fees		0.75	%		0.75	%		0.75	%
Distribution and/or service (12b‑1) fees		0.00	%		0.25	%		0.00	%
Other expenses		0.18	%		0.18	%		0.07	%
Total annual fund operating expenses		0.93	%		1.18	%		0.82	%
Fee waiver and/or expense reimbursement¹		0.00	%		0.00	%		0.00	%
Total annual fund operating expenses after fee waiver and/or expense reimbursement		0.93	%		1.18	%		0.82	%

Loomis, Sayles & Company, L.P. (“Loomis Sayles” or the “Adviser”) has given a binding contractual undertaking to the Fund to limit the amount of the Fund’s total annual fund operating expenses to 0.95%, 1.20% and 0.90% of the Fund’s average daily net assets for Institutional Class, Retail Class and Class N shares, respectively, exclusive of brokerage expenses, interest expense, taxes, acquired fund fees and expenses, organizational and extraordinary expenses, such as litigation and indemnification expenses. This undertaking is in effect through January 31, 2025 and may be terminated before then only with the consent of the Fund’s Board of Trustees. The Adviser will be permitted to recover, on a class by class basis, management fees waived and/or expenses reimbursed to the extent that expenses in later periods fall below both (1) the class’ applicable expense limitation. The Fund will not be obligated to repay any such waived/reimbursed fees and expenses more than one year after the end of the fiscal year in which the fees or expenses were waived/reimbursed.

Example


	1 year		3 years		5 years		10 years
Institutional Class	$	95	$	296	$	515	$	1,143
Retail Class	$	120	$	375	$	649	$	1,432
Class N	$	84	$	262	$	455	$	1,014

Loomis Sayles High Income Fund

Risk/Return:

rr_RiskReturnAbstract

Supplement to Prospectus [Text Block]

rr_SupplementToProspectusTextBlock

Supplement dated June 21, 2023 to the Prospectus and Summary Prospectus, each dated May 1, 2023, as

may be revised or supplemented from time to time, for the following fund:

LOOMIS SAYLES HIGH INCOME FUND

(each, a “Fund”)

LOOMIS SAYLES HIGH INCOME FUND

Effective July 1, 2023, Loomis, Sayles & Company, L.P. has given a binding contractual undertaking to the Fund to limit the amount of the Fund’s total annual fund operating expenses to 0.95%, 1.70%, 0.65%, 0.95% and 0.70% of the Fund’s average daily net assets for Class A, C, N, T and Y shares, respectively, exclusive of brokerage expenses, interest expense, taxes, acquired fund fees and expenses, organizational and extraordinary expenses, such as litigation and indemnification expenses. This undertaking is in effect through April 30, 2025.

Accordingly, the Annual Fund Operating Expenses table and the Example table within the section “Fund Fees & Expenses” are amended and restated as follows with respect to the Fund:

Annual Fund Operating Expenses

(expenses that you pay each year as a percentage of the value of your investment)


	Class A			Class C			Class N			Class T			Class Y
Management fees¹		0.55	%		0.55	%		0.55	%		0.55	%		0.55	%
Distribution and/or service (12b‑1) fees		0.25	%		1.00	%		0.00	%		0.25	%		0.00	%
Other expenses²		0.34	%		0.34	%		1.21	%		0.34	%³		0.34	%
Total annual fund operating expenses		1.14	%		1.89	%		1.76	%		1.14	%		0.89	%
Fee waiver and/or expense reimbursement^4,5		0.18	%		0.18	%		1.10	%		0.18	%		0.18	%
Total annual fund operating expenses after fee waiver and/or expense reimbursement		0.96	%		1.71	%		0.66	%		0.96	%		0.71	%

¹	The Fund’s operating expenses have been restated to reflect a reduction in management fees, effective as of July 1, 2023, as if reduction had been in effect during the fiscal year ended December 31, 2022. The information has been restated to better reflect anticipated expenses of the Fund.

³	Other expenses for Class T shares are estimated for the current fiscal year.

⁴

Loomis, Sayles & Company, L.P. (“Loomis Sayles” or the “Adviser”) has given a binding contractual undertaking to the Fund to limit the amount of the Fund’s total annual fund operating expenses to 0.95%, 1.70%, 0.65%, 0.95% and 0.70% of the Fund’s average daily net assets for Class A, C, N, T and Y shares, respectively, exclusive of brokerage expenses, interest expense, taxes, acquired fund fees and expenses, organizational and extraordinary expenses, such as litigation and indemnification expenses. This undertaking is in effect through April 30, 2025 and may be terminated before then only with the consent of the Fund’s Board of Trustees. The Adviser will be permitted to recover, on a class by class basis, management fees waived and/or expenses reimbursed to the extent that expenses in later periods fall below both (1) the class’ applicable expense limitation. The Fund will not be obligated to repay any such waived/reimbursed fees and expenses more than one year after the end of the fiscal year in which the fees or expenses were waived/reimbursed.

⁵

Example

This example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods (except where indicated). The example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses remain the same, except that the example is based on the Total Annual Fund Operating Expenses After Fee Waiver and/or Expense Reimbursement assuming that such waiver and/or reimbursement will only be in place through the dates noted above and on the Total Annual Fund Operating Expenses for the remaining periods. The example for Class C shares for the ten‑year period reflects the conversion to Class A shares after eight years. The example does not take into account brokerage commissions and other fees to financial intermediaries that you may pay on your purchases and sales of shares of the Fund. Although your actual costs may be higher or lower, based on these assumptions your costs would be:


If shares are redeemed:	1 year		3 years		5 years		10 years
Class A	$	519	$	740	$	995	$	1,723
Class C	$	274	$	561	$	990	$	1,988
Class N	$	67	$	351	$	759	$	1,900
Class T	$	345	$	570	$	830	$	1,572
Class Y	$	73	$	250	$	460	$	1,065


If shares are not redeemed:	1 year		3 years		5 years		10 years
Class C	$	174	$	561	$	990	$	1,988

Loomis Sayles Strategic Income Fund

Risk/Return:

rr_RiskReturnAbstract

Supplement to Prospectus [Text Block]

rr_SupplementToProspectusTextBlock

Supplement dated June 21, 2023 to the Prospectus and Summary Prospectus, each dated May 1, 2023, as

may be revised or supplemented from time to time, for the following fund:

LOOMIS SAYLES STRATEGIC INCOME FUND

(each, a “Fund”)

LOOMIS SAYLES STRATEGIC INCOME FUND

Effective July 1, 2023, Loomis, Sayles & Company, L.P. has given a binding contractual undertaking to the Fund to limit the amount of the Fund’s total annual fund operating expenses to 0.93%, 1.68%, 0.63%, 0.93%, 0.68% and 1.18% of the Fund’s average daily net assets for Class A, C, N, T, Y and Admin Class shares, respectively, exclusive of brokerage expenses, interest expense, taxes, acquired fund fees and expenses, organizational and extraordinary expenses, such as litigation and indemnification expenses. This undertaking is in effect through April 30, 2025.

Accordingly, the Annual Fund Operating Expenses table and the Example table within the section “Fund Fees & Expenses” are amended and restated as follows with respect to the Fund:

Annual Fund Operating Expenses

(expenses that you pay each year as a percentage of the value of your investment)


	Class A			Class C			Class N			Class T			Class Y			Admin Class
Management fees¹		0.57	%		0.57	%		0.57	%		0.57	%		0.57	%		0.57	%
Distribution and/or service (12b‑1) fees		0.25	%		1.00	%		0.00	%		0.25	%		0.00	%		0.25	%
Other expenses²		0.15	%		0.15	%		0.06	%		0.15	%³		0.15	%		0.40	%⁴
Total annual fund operating expenses		0.97	%		1.72	%		0.63	%		0.97	%		0.72	%		1.22	%
Fee waiver and/or expense reimbursement⁵		0.04	%		0.04	%		0.00	%		0.04	%		0.04	%		0.04	%
Total annual fund operating expenses after fee waiver and/or expense reimbursement		0.93	%		1.68	%		0.63	%		0.93	%		0.68	%		1.18	%

¹	The Fund’s operating expenses have been restated to reflect a reduction in management fees, effective as of July 1, 2023, as if reduction had been in effect during the fiscal year ended December 31, 2022. The information has been restated to better reflect anticipated expenses of the Fund.

²	Other expenses include acquired fund fees and expenses of less than 0.01%.

³	Other expenses for Class T shares are estimated for the current fiscal year.

⁴	Other expenses include an administrative service fee of 0.25% for Admin Class shares.

⁵

Loomis, Sayles & Company, L.P. (“Loomis Sayles” or the “Adviser”) has given a binding contractual undertaking to the Fund to limit the amount of the Fund’s total annual fund operating expenses to 0.93%, 1.68%, 0.63%, 0.93%, 0.68% and 1.18% of the Fund’s average daily net assets for Class A, C, N, T, Y and Admin Class shares, respectively, exclusive of brokerage expenses, interest expense, taxes, acquired fund fees and expenses, organizational and extraordinary expenses, such as litigation and indemnification expenses. This undertaking is in effect through April 30, 2025 and may be terminated before then only with the consent of the Fund’s Board of Trustees. The Adviser will be permitted to recover, on a class by class basis, management fees waived and/or expenses reimbursed to the extent that expenses in later periods fall below both (1) the class’ applicable expense limitation. The Fund will not be obligated to repay any such waived/reimbursed fees and expenses more than one year after the end of the fiscal year in which the fees or expenses were waived/reimbursed.

Example

This example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods (except where indicated). The example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses remain the same, except that the examples for Class A, C, T, Y and Admin Class are based on the Total Annual Fund Operating Expenses After Fee Waiver and/or Expense Reimbursement assuming that such waiver and/or reimbursement will only be in place through the dates noted above and on the Total Annual Fund Operating Expenses for the remaining periods. The example for Class C shares for the ten‑year period reflects the conversion to Class A shares after eight years. The example does not take into account brokerage commissions and other fees to financial intermediaries that you may pay on your purchases and sales of shares of the Fund. Although your actual costs may be higher or lower, based on these assumptions your costs would be:


If shares are redeemed:	1 year		3 years		5 years		10 years
Class A	$	516	$	714	$	931	$	1,558
Class C	$	271	$	535	$	926	$	1,825
Class N	$	64	$	202	$	351	$	786
Class T	$	343	$	544	$	766	$	1,403
Class Y	$	69	$	223	$	393	$	887
Admin Class	$	120	$	380	$	663	$	1,471


If shares are not redeemed:	1 year		3 years		5 years		10 years
Class C	$	171	$	535	$	926	$	1,825