15 Year Amortization Schedule Calculator

This 15-year amortization schedule calculator estimates the fixed monthly payment, total paid, and total interest for a loan repaid over 180 monthly payments. Enter the loan amount and annual APR to see the payment math; the schedule assumes a fixed rate and does not include lender-specific charges.

Formula

The monthly payment uses the standard fixed-payment amortization formula: M = P × r ÷ [1 − (1 + r)⁻ⁿ]. Here, M is the monthly payment in dollars, P is the starting principal in dollars, r is the monthly interest rate as a decimal, and n is the number of monthly payments. For a 15-year term, n = 15 × 12 = 180, and r = APR ÷ 1200 when APR is entered as a percentage per year.

Total payments are the rounded monthly payment multiplied by 180. Estimated total interest is total payments minus the original principal. Because the payment is rounded to cents before totals are calculated, this method reflects 180 equal cent-rounded payments; an actual final payment may be adjusted by a loan servicer.

Worked Example

Using the calculator’s default values, the loan amount is $20,000 and APR is 8%. The term is fixed at 15 years, or 180 months.

• Monthly rate: 8 ÷ 1200 = 0.0066667.
• Payment formula: $20,000 × 0.0066667 ÷ [1 − (1.0066667)⁻¹⁸⁰].
• Unrounded monthly payment is approximately $191.13; rounded to cents, the payment is $191.13.
• Total of 180 payments: $191.13 × 180 = $34,403.40.
• Estimated total interest: $34,403.40 − $20,000 = $14,403.40.

Assumptions

• The interest rate stays fixed throughout the 15-year term.
• Payments are equal, made monthly, and treated as occurring at the end of each monthly period.
• Interest is compounded monthly using APR divided by 12.
• The calculation excludes fees, taxes, insurance, PMI, escrow, and any charges not entered as loan principal.

What a 15-Year Amortization Schedule Shows

An amortization schedule breaks a loan into payment periods and shows how each payment is divided between interest and principal. Early in repayment, interest is calculated on a larger outstanding balance, so more of a level payment goes to interest. As principal falls, the interest portion generally shrinks and the principal portion grows.

This calculator gives the core figures for a 15-year, fixed-rate loan: payment, total of scheduled payments, and estimated interest. It does not print all 180 rows. To make a row-by-row schedule, start with the opening balance; calculate that month’s interest as balance × APR ÷ 1200; subtract interest from the payment to find principal repaid; then subtract principal repaid from the balance. Repeat for each month, allowing for rounding and any final-payment adjustment.

For example, at the default 8% APR, the first month’s estimated interest is $20,000 × 0.0066667, or about $133.33. From a $191.13 payment, approximately $57.80 reduces principal, leaving an estimated balance of $19,942.20. Figures in a lender’s statement can differ by a few cents because of payment dates, daily-interest methods, rounding, or fees added to the balance.

When to Use This Estimate

Use the calculation to understand the arithmetic of a fixed 15-year repayment period, compare hypothetical loan amounts or APR inputs, or check whether a payment quote is in the expected range under the same assumptions. Enter the principal that will actually accrue interest and the APR supplied in the lender’s disclosure. APR can reflect details beyond a simple nominal interest rate, while this formula applies the entered APR as a monthly rate and does not separately model financed fees.

A 15-year schedule has fewer payments than a longer schedule, but the payment amount depends on both principal and APR. The calculator does not determine whether a payment is affordable, whether an application will be approved, or whether a particular loan is appropriate. It only performs fixed-rate payment arithmetic from the values entered.

How to Read the Results

Monthly payment is the calculated scheduled payment toward principal and interest. It is not necessarily the full amount due if the loan also bills taxes, insurance, mortgage insurance, or other items. Total of 180 payments multiplies the cent-rounded payment by 180, and total interest subtracts the original principal from that total.

The schedule assumes all payments arrive as planned. Extra payments, skipped or late payments, a variable rate, or a change in the outstanding balance will alter the payoff path and actual interest. If a lender’s quoted payment includes costs outside principal and interest, compare like components rather than treating the quoted total as the calculator’s payment.

Common Mistakes and Limits

Enter APR as a percentage, such as 8 for 8%, not as 0.08; the calculator divides the percentage by 1200 to get a monthly decimal rate. Check that the principal is the amount on which interest accrues, not a desired cash amount that excludes financed charges. Do not multiply the payment by 15: monthly payments require 180 periods.

Rounding each payment to cents before multiplying can produce a small difference from calculations that retain extra decimal places throughout. Actual loan servicing may accrue interest daily, use different due dates, or adjust the last payment. The calculator also cannot reproduce contract terms such as fees, variable-rate changes, payment holidays, or prepayment treatment. Get the exact APR and payment details from the lender’s disclosure. This result is an estimate, and the lender’s disclosure gives the exact figures.

Frequently Asked Questions

How many payments are in a 15-year amortization schedule?
With one payment each month and no skipped periods, there are 15 × 12 = 180 scheduled payments.

Does the monthly payment include property taxes or insurance?
No. The formula estimates principal and interest only; taxes, insurance, PMI, and escrow are not included.

Why does the interest portion change over time?
Each period’s interest is based on the remaining balance. As scheduled payments reduce principal, the next period generally accrues less interest.

Can I use this for a variable-rate loan?
Only as a fixed-rate illustration. A variable rate can change the payment or repayment pattern, which this calculation does not model.

Why might a lender’s figure differ by a few cents?
Payment timing, daily rather than monthly interest accrual, rounding conventions, financed charges, and final-payment adjustments can cause differences.

Final Thoughts

A 15-year amortization calculation turns principal and APR into a clear estimate of the monthly payment and scheduled interest. Treat it as a planning illustration, then use the lender’s disclosure and payment schedule for the contract-specific amounts.

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in p | Loan amount | $ | 20000 | 1 | 100000000
in apr | Interest rate (APR) | % | 8 | 0.01 | 100
out pmt | Monthly payment | $ | round(p * (apr / 1200) / (1 - (1 + apr / 1200) ^ -180), 2) | 2
out tot | Total of 180 payments | $ | pmt * 180 | 2
out int | Total interest | $ | tot - p | 2