As of September 30, 2020 and 2019, we had the following long-term borrowing obligations:

(in thousands)	September 30,
	2020			2019
4.000% Senior notes due 2028	$	500,000		$	—
3.625% Senior notes due 2025		500,000			—
6.000% Senior notes due 2024		—			500,000
Credit facility revolver⁽¹⁾		18,000			173,125
Total debt		1,018,000			673,125
Unamortized debt issuance costs for the Senior notes⁽²⁾		(12,686	)		(3,991	)
Total debt, net of issuance costs⁽³⁾	$	1,005,314		$	669,134

In February 2020, we issued $500 million in aggregate principal amount of 4.0% senior, unsecured long-term debt at par value, due in 2028 (the 2028 notes) and $500 million in aggregate principal amount of 3.625% senior, unsecured long-term debt at par value, due in 2025 (the 2025 notes). In the second quarter of 2020, we used $460 million of the net proceeds from the sale of the notes to repay a portion of the outstanding revolving loan under our credit facility. In the third quarter of 2020, we used the remaining net proceeds from the sale of the notes to redeem the $500 million aggregate principal amount of our outstanding 6.0% senior notes due in 2024 (the 2024 notes). The redemption price for the 2024 notes was 103% of the aggregate principal amount of the notes, plus accrued and unpaid interest.

As of September 30, 2020, the total estimated fair value of the 2028 and 2025 senior notes was approximately $515.1 million and $507.5 million respectively, based on quoted prices for the notes on that date.

We were in compliance with all the covenants for all of our senior notes as of September 30, 2020.

Interest on the 2028 and 2025 notes is payable semi-annually on February 15 and August 15. The debt indenture for the 2028 and 2025 notes includes covenants that limit our ability to, among other things, incur additional debt, grant liens on our properties or capital stock, enter into sale and leaseback transactions or asset sales, and make capital distributions.

We may, on one or more occasions, redeem the 2025 and 2028 notes in whole or in part at specified redemption prices. In certain circumstances constituting a change of control, we would be required to make an offer to repurchase the notes at a purchase price equal to 101% of the aggregate principal amount of the notes, plus accrued and unpaid interest. Our ability to repurchase the notes upon such event may be limited by law, by the indenture associated with the notes, by our then-available financial resources or by the terms of other agreements to which we may be party at such time. If we fail to repurchase the notes as required by the indenture, it would constitute an event of default under the indenture which, in turn, may also constitute an event of default under other obligations.

In February 2020, we entered into a Third Amended and Restated Credit Agreement with JPMorgan Chase Bank, N.A., as Administrative Agent, for a new secured multi-currency bank credit facility with a syndicate of banks. The new credit facility replaced our prior credit facility. As with the prior credit facility, we expect to use the new credit facility for general corporate purposes, including acquisitions of businesses, share repurchases and working capital requirements. As of September 30, 2020, the fair value of our credit facility approximates its book value.

The credit facility consists of a $1 billion revolving credit facility, which may be increased by up to an additional $500 million in the aggregate if the existing or additional lenders are willing to make such increased commitments. As of September 30, 2020, unused commitments under our credit facility were approximately $982.0 million. The maturity date of the credit facility is February 13, 2025, when all remaining amounts outstanding will be due and payable. The revolving loan commitment does not require amortization of principal and may be repaid in whole or in part prior to the scheduled maturity date at our option without penalty or premium.

PTC and certain eligible foreign subsidiaries are eligible borrowers under the credit facility. Any borrowings by PTC Inc. under the credit facility would be guaranteed by PTC Inc.’s material domestic subsidiaries that become parties to the subsidiary guaranty, if any. As of the filing of this Form 10-K, there are no subsidiary guarantors of the obligations under the credit facility. Any borrowings by eligible foreign subsidiary borrowers would be guaranteed by PTC Inc. and any subsidiary guarantors. As of the filing of this Form 10-K, no funds were borrowed by an eligible foreign subsidiary borrower. In addition, owned property (including equity interests) of PTC and certain of its material domestic subsidiaries' owned property is subject to first priority perfected liens in favor of the lenders under this credit facility. 100% of the voting equity interests of certain of PTC’s domestic subsidiaries and 65% of its material first-tier foreign subsidiaries are pledged as collateral for the obligations under the credit facility.

Loans under the credit facility bear interest at variable rates which reset every 30 to 180 days depending on the rate and period selected by PTC as described below. As of September 30, 2020, the annual rate for borrowing outstanding was 1.81%. Interest rates on borrowings outstanding under the credit facility range from 1.25% to 1.75% above an adjusted London Interbank Offering Rate (LIBOR) for Euro currency borrowings or range from 0.25% to 0.75% above the defined base rate (the greater of the Prime Rate, the NYFRB rate plus 0.5%, or an adjusted LIBOR plus 1%) for base rate borrowings, in each case based upon PTC’s total leverage ratio. Additionally, PTC may borrow certain foreign currencies at rates set in the same range above the respective LIBOR for those currencies, based on PTC’s total leverage ratio. A quarterly commitment fee on the undrawn portion of the credit facility is required, ranging from 0.175% to 0.30% per annum, based upon PTC’s total leverage ratio.

The credit facility limits PTC’s and its subsidiaries’ ability to, among other things: incur additional indebtedness; incur liens or guarantee obligations; pay dividends (other than to PTC) and make other distributions; make investments and enter into joint ventures; dispose of assets; and engage in transactions with affiliates, except on an arms-length basis. Under the credit facility, PTC and its material domestic

subsidiaries may not invest cash or property in, or loan to, PTC’s foreign subsidiaries in aggregate amounts exceeding $100 million for any purpose and an additional $200 million for acquisitions of businesses. In addition, under the credit facility, PTC and its subsidiaries must maintain the following financial ratios:

As of September 30, 2020, our total leverage ratio was 2.34 to 1.00, our senior secured leverage ratio was 0.08 to 1.00 and our interest coverage ratio was 5.85 to 1.00 and we were in compliance with all financial and operating covenants of the credit facility.

Any failure to comply with the financial or operating covenants of the credit facility would prevent PTC from being able to borrow additional funds, and would constitute a default, permitting the lenders to, among other things, accelerate the amounts outstanding, including all accrued interest and unpaid fees, under the credit facility and to terminate the credit facility. A change in control of PTC, as defined in the agreement, also constitutes an event of default, permitting the lenders to accelerate the indebtedness and terminate the credit facility.

We incurred $2.0 million in financing costs in connection with the February 2020 credit facility and $1.0 million in connection with a November 2019 amendment to our prior credit facility. These origination costs are recorded as deferred debt issuance costs and are included in other assets. Financing costs are expensed over the remaining term of the obligations.

In 2020, 2019 and 2018, we incurred interest expense of $76.4 million, $43.0 million, and $41.7 million, respectively, and paid $60.6 million, $40.8 million and $39.8 million, respectively, of interest on our debt. Additionally, in the third quarter of 2020, we paid $15.0 million in penalties for the early redemption of the 2024 notes. The average interest rate on borrowings outstanding during 2020, 2019 and 2018 was approximately 4.3%, 5.4% and 5.2%, respectively.