497

The interactive data file included as an exhibit to this filing relates to the supplement to the prospectus for Columbia Acorn International Select filed pursuant to Rule 497(e) under the Securities Act of 1933, as amended, on August 10, 2020 (Accession No. 0001193125-20-214579), which is incorporated herein by reference.

XML

Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Document Type	dei_DocumentType	497
Document Period End Date	dei_DocumentPeriodEndDate	Dec. 31, 2019
Registrant Name	dei_EntityRegistrantName	COLUMBIA ACORN TRUST
Central Index Key	dei_EntityCentralIndexKey	0000002110
Amendment Flag	dei_AmendmentFlag	false
Document Creation Date	dei_DocumentCreationDate	Aug. 10, 2020
Document Effective Date	dei_DocumentEffectiveDate	Aug. 10, 2020
Prospectus Date	rr_ProspectusDate	May 01, 2020
Entity Inv Company Type	dei_EntityInvCompanyType	N-1A

XML

May 01, 2020

Supplement dated August 10, 2020

to the Prospectus, as supplemented, of the following Fund (the Fund):

Fund	Prospectus Dated
Columbia Acorn Trust
Columbia Acorn International SelectSM	5/1/2020

The reorganization of Columbia Select International Equity Fund with and into Columbia Acorn International Select (the Fund) closed on August 7, 2020. Therefore, effective immediately the Investment Manager's contractual agreement to waive fees and reimburse certain expenses of the Fund is extended through April 30, 2022 as described in this Supplement.

1. The "Summary of the Fund - Fees and Expenses of the Fund" section of the Prospectus is revised to replace the "Shareholder Fees" and "Annual Fund Operating Expenses" tables, and the information under the caption "Example" with the following information:

Shareholder Fees (fees paid directly from your investment)
	Class A	Class C	Classes Adv, Inst, Inst2, and Inst3
Maximum sales charge (load) imposed on purchases (as a % of offering price)	5.75%	None	None
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	1.00% (a)	1.00% (b)	None

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
	Class A	Class Adv	Class C	Class Inst	Class Inst2	Class Inst3
Management fees	0.89%	0.89%	0.89%	0.89%	0.89%	0.89%
Distribution and/or service (12b-1) fees	0.25%	0.00%	1.00%	0.00%	0.00%	0.00%
Other expenses(c)	0.39%	0.39%	0.39%	0.39%	0.32%	0.27%
Total annual Fund operating expenses	1.53%	1.28%	2.28%	1.28%	1.21%	1.16%
Less: Fee waivers and/or expense reimbursements(d)	(0.25%)	(0.25%)	(0.25%)	(0.25%)	(0.31%)	(0.31%)
Total annual Fund operating expenses after fee waivers and/or expense reimbursements	1.28%	1.03%	2.03%	1.03%	0.90%	0.85%

(a)	This charge is imposed on certain investments of between $1 million and $50 million redeemed within 18 months after purchase, as follows: 1.00% if redeemed within 12 months after purchase, and 0.50% if redeemed more than 12, but less than 18, months after purchase, with certain limited exceptions.
(b)	This charge applies to redemptions within 12 months after purchase, with certain limited exceptions.
(c)	Other expenses have been restated to reflect current fees paid by the Fund.
(d)	Columbia Wanger Asset Management, LLC (the Investment Manager) has contractually agreed to waive fees and reimburse certain expenses of the Fund, through April 30, 2022, so that ordinary operating expenses (excluding any reorganization costs, transaction costs and certain other investment-related expenses, interest and fees on borrowings and expenses associated with the Fund’s investment in other investment companies, if any) do not exceed the annual rates of 1.28% for Class A shares, 1.03% for Class Adv shares, 2.03% for Class C shares, 1.03% for Class Inst shares, 0.90% for Class Inst2 shares and 0.85% for Class Inst3 shares. This arrangement may only be amended or terminated with approval from the Fund’s Board of Trustees and the Investment Manager.

Example

The following 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 illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

■ you invest $10,000 in the applicable class of Fund shares for the periods indicated,

■ your investment has a 5% return each year, and

■ the Fund’s total annual operating expenses remain the same as shown in the Annual Fund Operating Expenses table above.

Since the waivers and/or reimbursements shown in the Annual Fund Operating Expenses table above expire as indicated in the preceding table, they are only reflected in the 1 year example and the first year of the other examples. Although your actual costs may be higher or lower, based on the assumptions listed above, your costs would be:

	1 year	3 years	5 years	10 years
Class A (whether or not shares are redeemed)	$698	$1,007	$1,339	$2,274
Class Adv (whether or not shares are redeemed)	$105	$ 381	$ 678	$1,523
Class C (assuming redemption of all shares at the end of the period)	$306	$ 688	$1,197	$2,596
Class C (assuming no redemption of shares)	$206	$ 688	$1,197	$2,596
Class Inst (whether or not shares are redeemed)	$105	$ 381	$ 678	$1,523
Class Inst2 (whether or not shares are redeemed)	$ 92	$ 353	$ 635	$1,438
Class Inst3 (whether or not shares are redeemed)	$ 87	$ 338	$ 608	$1,381

The rest of the section remains the same.

XML

Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Registrant Name

dei_EntityRegistrantName

COLUMBIA ACORN TRUST

Prospectus Date

rr_ProspectusDate

May 01, 2020

Supplement to Prospectus [Text Block]

rr_SupplementToProspectusTextBlock

Supplement dated August 10, 2020

to the Prospectus, as supplemented, of the following Fund (the Fund):

Fund	Prospectus Dated
Columbia Acorn Trust
Columbia Acorn International SelectSM	5/1/2020

The reorganization of Columbia Select International Equity Fund with and into Columbia Acorn International Select (the Fund) closed on August 7, 2020. Therefore, effective immediately the Investment Manager's contractual agreement to waive fees and reimburse certain expenses of the Fund is extended through April 30, 2022 as described in this Supplement.

1. The "Summary of the Fund - Fees and Expenses of the Fund" section of the Prospectus is revised to replace the "Shareholder Fees" and "Annual Fund Operating Expenses" tables, and the information under the caption "Example" with the following information:

Shareholder Fees (fees paid directly from your investment)
	Class A	Class C	Classes Adv, Inst, Inst2, and Inst3
Maximum sales charge (load) imposed on purchases (as a % of offering price)	5.75%	None	None
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	1.00% (a)	1.00% (b)	None

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
	Class A	Class Adv	Class C	Class Inst	Class Inst2	Class Inst3
Management fees	0.89%	0.89%	0.89%	0.89%	0.89%	0.89%
Distribution and/or service (12b-1) fees	0.25%	0.00%	1.00%	0.00%	0.00%	0.00%
Other expenses(c)	0.39%	0.39%	0.39%	0.39%	0.32%	0.27%
Total annual Fund operating expenses	1.53%	1.28%	2.28%	1.28%	1.21%	1.16%
Less: Fee waivers and/or expense reimbursements(d)	(0.25%)	(0.25%)	(0.25%)	(0.25%)	(0.31%)	(0.31%)
Total annual Fund operating expenses after fee waivers and/or expense reimbursements	1.28%	1.03%	2.03%	1.03%	0.90%	0.85%

(a)	This charge is imposed on certain investments of between $1 million and $50 million redeemed within 18 months after purchase, as follows: 1.00% if redeemed within 12 months after purchase, and 0.50% if redeemed more than 12, but less than 18, months after purchase, with certain limited exceptions.
(b)	This charge applies to redemptions within 12 months after purchase, with certain limited exceptions.
(c)	Other expenses have been restated to reflect current fees paid by the Fund.
(d)	Columbia Wanger Asset Management, LLC (the Investment Manager) has contractually agreed to waive fees and reimburse certain expenses of the Fund, through April 30, 2022, so that ordinary operating expenses (excluding any reorganization costs, transaction costs and certain other investment-related expenses, interest and fees on borrowings and expenses associated with the Fund’s investment in other investment companies, if any) do not exceed the annual rates of 1.28% for Class A shares, 1.03% for Class Adv shares, 2.03% for Class C shares, 1.03% for Class Inst shares, 0.90% for Class Inst2 shares and 0.85% for Class Inst3 shares. This arrangement may only be amended or terminated with approval from the Fund’s Board of Trustees and the Investment Manager.

Example

The following 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 illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

■ you invest $10,000 in the applicable class of Fund shares for the periods indicated,

■ your investment has a 5% return each year, and

■ the Fund’s total annual operating expenses remain the same as shown in the Annual Fund Operating Expenses table above.

Since the waivers and/or reimbursements shown in the Annual Fund Operating Expenses table above expire as indicated in the preceding table, they are only reflected in the 1 year example and the first year of the other examples. Although your actual costs may be higher or lower, based on the assumptions listed above, your costs would be:

	1 year	3 years	5 years	10 years
Class A (whether or not shares are redeemed)	$698	$1,007	$1,339	$2,274
Class Adv (whether or not shares are redeemed)	$105	$ 381	$ 678	$1,523
Class C (assuming redemption of all shares at the end of the period)	$306	$ 688	$1,197	$2,596
Class C (assuming no redemption of shares)	$206	$ 688	$1,197	$2,596
Class Inst (whether or not shares are redeemed)	$105	$ 381	$ 678	$1,523
Class Inst2 (whether or not shares are redeemed)	$ 92	$ 353	$ 635	$1,438
Class Inst3 (whether or not shares are redeemed)	$ 87	$ 338	$ 608	$1,381

The rest of the section remains the same.

Columbia Acorn International Select

Risk/Return:

rr_RiskReturnAbstract

Supplement to Prospectus [Text Block]

rr_SupplementToProspectusTextBlock

Supplement dated August 10, 2020

to the Prospectus, as supplemented, of the following Fund (the Fund):

Fund	Prospectus Dated
Columbia Acorn Trust
Columbia Acorn International SelectSM	5/1/2020

The reorganization of Columbia Select International Equity Fund with and into Columbia Acorn International Select (the Fund) closed on August 7, 2020. Therefore, effective immediately the Investment Manager's contractual agreement to waive fees and reimburse certain expenses of the Fund is extended through April 30, 2022 as described in this Supplement.

1. The "Summary of the Fund - Fees and Expenses of the Fund" section of the Prospectus is revised to replace the "Shareholder Fees" and "Annual Fund Operating Expenses" tables, and the information under the caption "Example" with the following information:

Shareholder Fees (fees paid directly from your investment)
	Class A	Class C	Classes Adv, Inst, Inst2, and Inst3
Maximum sales charge (load) imposed on purchases (as a % of offering price)	5.75%	None	None
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	1.00% (a)	1.00% (b)	None

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
	Class A	Class Adv	Class C	Class Inst	Class Inst2	Class Inst3
Management fees	0.89%	0.89%	0.89%	0.89%	0.89%	0.89%
Distribution and/or service (12b-1) fees	0.25%	0.00%	1.00%	0.00%	0.00%	0.00%
Other expenses(c)	0.39%	0.39%	0.39%	0.39%	0.32%	0.27%
Total annual Fund operating expenses	1.53%	1.28%	2.28%	1.28%	1.21%	1.16%
Less: Fee waivers and/or expense reimbursements(d)	(0.25%)	(0.25%)	(0.25%)	(0.25%)	(0.31%)	(0.31%)
Total annual Fund operating expenses after fee waivers and/or expense reimbursements	1.28%	1.03%	2.03%	1.03%	0.90%	0.85%

(a)	This charge is imposed on certain investments of between $1 million and $50 million redeemed within 18 months after purchase, as follows: 1.00% if redeemed within 12 months after purchase, and 0.50% if redeemed more than 12, but less than 18, months after purchase, with certain limited exceptions.
(b)	This charge applies to redemptions within 12 months after purchase, with certain limited exceptions.
(c)	Other expenses have been restated to reflect current fees paid by the Fund.
(d)	Columbia Wanger Asset Management, LLC (the Investment Manager) has contractually agreed to waive fees and reimburse certain expenses of the Fund, through April 30, 2022, so that ordinary operating expenses (excluding any reorganization costs, transaction costs and certain other investment-related expenses, interest and fees on borrowings and expenses associated with the Fund’s investment in other investment companies, if any) do not exceed the annual rates of 1.28% for Class A shares, 1.03% for Class Adv shares, 2.03% for Class C shares, 1.03% for Class Inst shares, 0.90% for Class Inst2 shares and 0.85% for Class Inst3 shares. This arrangement may only be amended or terminated with approval from the Fund’s Board of Trustees and the Investment Manager.

Example

The following 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 illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

■ you invest $10,000 in the applicable class of Fund shares for the periods indicated,

■ your investment has a 5% return each year, and

■ the Fund’s total annual operating expenses remain the same as shown in the Annual Fund Operating Expenses table above.

Since the waivers and/or reimbursements shown in the Annual Fund Operating Expenses table above expire as indicated in the preceding table, they are only reflected in the 1 year example and the first year of the other examples. Although your actual costs may be higher or lower, based on the assumptions listed above, your costs would be:

	1 year	3 years	5 years	10 years
Class A (whether or not shares are redeemed)	$698	$1,007	$1,339	$2,274
Class Adv (whether or not shares are redeemed)	$105	$ 381	$ 678	$1,523
Class C (assuming redemption of all shares at the end of the period)	$306	$ 688	$1,197	$2,596
Class C (assuming no redemption of shares)	$206	$ 688	$1,197	$2,596
Class Inst (whether or not shares are redeemed)	$105	$ 381	$ 678	$1,523
Class Inst2 (whether or not shares are redeemed)	$ 92	$ 353	$ 635	$1,438
Class Inst3 (whether or not shares are redeemed)	$ 87	$ 338	$ 608	$1,381

The rest of the section remains the same.

Shareholder Fees Caption [Text]

rr_ShareholderFeesCaption

Shareholder Fees (fees paid directly from your investment)

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

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

Fee Waiver or Reimbursement over Assets, Date of Termination

rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination

April 30, 2022

Expenses Restated to Reflect Current [Text]

rr_ExpensesRestatedToReflectCurrent

Other expenses have been restated to reflect current fees paid by the Fund.

Expense Example [Heading]

rr_ExpenseExampleHeading

Example

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

The following 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 illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that:

• you invest $10,000 in the applicable class of Fund shares for the periods indicated,

• your investment has a 5% return each year, and

• the Fund’s total annual operating expenses remain the same as shown in the Annual Fund Operating Expenses table above.

Since the waivers and/or reimbursements shown in the Annual Fund Operating Expenses table above expire as indicated in the preceding table, they are only reflected in the 1 year example and the first year of the other examples. Although your actual costs may be higher or lower, based on the assumptions listed above, your costs would be:

Columbia Acorn International Select | Class A

Risk/Return:

rr_RiskReturnAbstract

Maximum sales charge (load) imposed on purchases (as a % of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

5.75%

Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)

rr_MaximumDeferredSalesChargeOverOther

1.00%

^[1]

Management fees

rr_ManagementFeesOverAssets

0.89%

Distribution and/or service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other expenses

rr_OtherExpensesOverAssets

0.39%

^[2]

Total annual Fund operating expenses

rr_ExpensesOverAssets

1.53%

Less: Fee waivers and/or expense reimbursements

rr_FeeWaiverOrReimbursementOverAssets

(0.25%)

^[3]

Total annual Fund operating expenses after fee waivers and/or expense reimbursements

rr_NetExpensesOverAssets

1.28%

Expenses Deferred Charges [Text Block]

rr_ExpensesDeferredChargesTextBlock

This charge is imposed on certain investments of between $1 million and $50 million redeemed within 18 months after purchase, as follows: 1.00% if redeemed within 12 months after purchase, and 0.50% if redeemed more than 12, but less than 18, months after purchase, with certain limited exceptions.

1 year

rr_ExpenseExampleYear01

$ 698

3 years

rr_ExpenseExampleYear03

1,007

5 years

rr_ExpenseExampleYear05

1,339

10 years

rr_ExpenseExampleYear10

2,274

1 year

rr_ExpenseExampleNoRedemptionYear01

698

3 years

rr_ExpenseExampleNoRedemptionYear03

1,007

5 years

rr_ExpenseExampleNoRedemptionYear05

1,339

10 years

rr_ExpenseExampleNoRedemptionYear10

$ 2,274

Columbia Acorn International Select | Class Adv

Risk/Return:

rr_RiskReturnAbstract

Maximum sales charge (load) imposed on purchases (as a % of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)

rr_MaximumDeferredSalesChargeOverOther

none

Management fees

rr_ManagementFeesOverAssets

0.89%

Distribution and/or service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.39%

^[2]

Total annual Fund operating expenses

rr_ExpensesOverAssets

1.28%

Less: Fee waivers and/or expense reimbursements

rr_FeeWaiverOrReimbursementOverAssets

(0.25%)

^[3]

Total annual Fund operating expenses after fee waivers and/or expense reimbursements

rr_NetExpensesOverAssets

1.03%

1 year

rr_ExpenseExampleYear01

$ 105

3 years

rr_ExpenseExampleYear03

381

5 years

rr_ExpenseExampleYear05

678

10 years

rr_ExpenseExampleYear10

1,523

1 year

rr_ExpenseExampleNoRedemptionYear01

105

3 years

rr_ExpenseExampleNoRedemptionYear03

381

5 years

rr_ExpenseExampleNoRedemptionYear05

678

10 years

rr_ExpenseExampleNoRedemptionYear10

$ 1,523

Columbia Acorn International Select | Class C

Risk/Return:

rr_RiskReturnAbstract

Maximum sales charge (load) imposed on purchases (as a % of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)

rr_MaximumDeferredSalesChargeOverOther

1.00%

^[4]

Management fees

rr_ManagementFeesOverAssets

0.89%

Distribution and/or service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

1.00%

Other expenses

rr_OtherExpensesOverAssets

0.39%

^[2]

Total annual Fund operating expenses

rr_ExpensesOverAssets

2.28%

Less: Fee waivers and/or expense reimbursements

rr_FeeWaiverOrReimbursementOverAssets

(0.25%)

^[3]

Total annual Fund operating expenses after fee waivers and/or expense reimbursements

rr_NetExpensesOverAssets

2.03%

Expenses Deferred Charges [Text Block]

rr_ExpensesDeferredChargesTextBlock

This charge applies to redemptions within 12 months after purchase, with certain limited exceptions.

1 year

rr_ExpenseExampleYear01

$ 306

3 years

rr_ExpenseExampleYear03

688

5 years

rr_ExpenseExampleYear05

1,197

10 years

rr_ExpenseExampleYear10

2,596

1 year

rr_ExpenseExampleNoRedemptionYear01

206

3 years

rr_ExpenseExampleNoRedemptionYear03

688

5 years

rr_ExpenseExampleNoRedemptionYear05

1,197

10 years

rr_ExpenseExampleNoRedemptionYear10

$ 2,596

Columbia Acorn International Select | Class Inst

Risk/Return:

rr_RiskReturnAbstract

Maximum sales charge (load) imposed on purchases (as a % of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)

rr_MaximumDeferredSalesChargeOverOther

none

Management fees

rr_ManagementFeesOverAssets

0.89%

Distribution and/or service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.39%

^[2]

Total annual Fund operating expenses

rr_ExpensesOverAssets

1.28%

Less: Fee waivers and/or expense reimbursements

rr_FeeWaiverOrReimbursementOverAssets

(0.25%)

^[3]

Total annual Fund operating expenses after fee waivers and/or expense reimbursements

rr_NetExpensesOverAssets

1.03%

1 year

rr_ExpenseExampleYear01

$ 105

3 years

rr_ExpenseExampleYear03

381

5 years

rr_ExpenseExampleYear05

678

10 years

rr_ExpenseExampleYear10

1,523

1 year

rr_ExpenseExampleNoRedemptionYear01

105

3 years

rr_ExpenseExampleNoRedemptionYear03

381

5 years

rr_ExpenseExampleNoRedemptionYear05

678

10 years

rr_ExpenseExampleNoRedemptionYear10

$ 1,523

Columbia Acorn International Select | Class Inst2

Risk/Return:

rr_RiskReturnAbstract

Maximum sales charge (load) imposed on purchases (as a % of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)

rr_MaximumDeferredSalesChargeOverOther

none

Management fees

rr_ManagementFeesOverAssets

0.89%

Distribution and/or service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.32%

^[2]

Total annual Fund operating expenses

rr_ExpensesOverAssets

1.21%

Less: Fee waivers and/or expense reimbursements

rr_FeeWaiverOrReimbursementOverAssets

(0.31%)

^[3]

Total annual Fund operating expenses after fee waivers and/or expense reimbursements

rr_NetExpensesOverAssets

0.90%

1 year

rr_ExpenseExampleYear01

$ 92

3 years

rr_ExpenseExampleYear03

353

5 years

rr_ExpenseExampleYear05

635

10 years

rr_ExpenseExampleYear10

1,438

1 year

rr_ExpenseExampleNoRedemptionYear01

92

3 years

rr_ExpenseExampleNoRedemptionYear03

353

5 years

rr_ExpenseExampleNoRedemptionYear05

635

10 years

rr_ExpenseExampleNoRedemptionYear10

$ 1,438

Columbia Acorn International Select | Class Inst3

Risk/Return:

rr_RiskReturnAbstract

Maximum sales charge (load) imposed on purchases (as a % of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)

rr_MaximumDeferredSalesChargeOverOther

none

Management fees

rr_ManagementFeesOverAssets

0.89%

Distribution and/or service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.27%

^[2]

Total annual Fund operating expenses

rr_ExpensesOverAssets

1.16%

^[3]

Less: Fee waivers and/or expense reimbursements

rr_FeeWaiverOrReimbursementOverAssets

(0.31%)

^[3]

Total annual Fund operating expenses after fee waivers and/or expense reimbursements

rr_NetExpensesOverAssets

0.85%

1 year

rr_ExpenseExampleYear01

$ 87

3 years

rr_ExpenseExampleYear03

338

5 years

rr_ExpenseExampleYear05

608

10 years

rr_ExpenseExampleYear10

1,381

1 year

rr_ExpenseExampleNoRedemptionYear01

87

3 years

rr_ExpenseExampleNoRedemptionYear03

338

5 years

rr_ExpenseExampleNoRedemptionYear05

608

10 years

rr_ExpenseExampleNoRedemptionYear10

$ 1,381

[1] This charge is imposed on certain investments of between $1 million and $50 million redeemed within 18 months after purchase, as follows: 1.00% if redeemed within 12 months after purchase, and 0.50% if redeemed more than 12, but less than 18, months after purchase, with certain limited exceptions.

[2] Other expenses have been restated to reflect current fees paid by the Fund.

[3] Columbia Wanger Asset Management, LLC (the Investment Manager) has contractually agreed to waive fees and reimburse certain expenses of the Fund, through April 30, 2022, so that ordinary operating expenses (excluding any reorganization costs, transaction costs and certain other investment-related expenses, interest and fees on borrowings and expenses associated with the Fund’s investment in other investment companies, if any) do not exceed the annual rates of 1.28% for Class A shares, 1.03% for Class Adv shares, 2.03% for Class C shares, 1.03% for Class Inst shares, 0.90% for Class Inst2 shares and 0.85% for Class Inst3 shares. This arrangement may only be amended or terminated with approval from the Fund’s Board of Trustees and the Investment Manager.

[4] This charge applies to redemptions within 12 months after purchase, with certain limited exceptions.

XML

Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	COLUMBIA ACORN TRUST
Prospectus Date	rr_ProspectusDate	May 01, 2020
Document Creation Date	dei_DocumentCreationDate	Aug. 10, 2020