Free Amortization Schedule With Extra Payments

A free amortization schedule with extra payments shows how each regular payment and additional principal payment changes your loan balance, interest, and payoff timeline. Enter the loan amount, APR, term, and planned extra monthly payment to estimate the payment-by-payment schedule and total interest.

Formula

The scheduled payment uses the standard fixed-payment loan formula, rounded to cents:

PMT = round[P × r ÷ (1 − (1 + r)⁻ⁿ), 2]

• P is the starting principal, in dollars.
• r is the monthly rate, calculated as APR ÷ 1,200.
• n is the number of monthly payments, calculated as loan term in years × 12.
• PMT is the scheduled monthly payment, in dollars.

The balance after k payments, when the same extra amount is added to each payment, is estimated as B_k = max[0, P(1 + r)^k − (PMT + E)((1 + r)^k − 1) ÷ r]. Here, E is extra principal per month in dollars, and k is the number of months. The calculator displays the 12-month balance. Interest without extra payments is PMT × n − P, using the rounded scheduled payment.

Worked Example

Using the defaults—$20,000 principal, 8% APR, five years, and $100 extra principal each month—the monthly rate is 0.08 ÷ 12 = 0.0066667, and the term is 5 × 12 = 60 months.

1. Scheduled payment: $20,000 × 0.0066667 ÷ [1 − (1.0066667)⁻⁶⁰] = $405.53 per month after rounding.
2. Interest without extra payments: $405.53 × 60 − $20,000 = $4,331.80.
3. For the balance after 12 months, the amount paid toward the formula each month is $405.53 + $100 = $505.53. Substituting k = 12 gives a balance of approximately $15,245.08.

The last figure is an estimate from the balance formula using the rounded scheduled payment and a constant additional payment. A real lender may calculate interest and apply payments differently, so a lender-generated schedule can differ slightly.

Assumptions

• The interest rate is fixed for the modeled term.
• Payments are monthly, with the first payment one month after the starting balance; extra principal is added with each payment.
• Interest accrues monthly at APR ÷ 12. This is a standard estimate, not a daily-interest calculation.
• The calculation excludes fees, taxes, insurance, PMI, escrow, and any charges or payment changes not entered.

How Extra Payments Change Amortization

An amortization schedule separates each payment into interest and principal. Interest is calculated on the outstanding balance, so early payments on a typical fixed-rate loan devote a larger share to interest. As principal falls, the interest portion generally falls and more of each scheduled payment reduces principal.

An additional payment applied directly to principal reduces the balance sooner. Because subsequent interest is calculated on a smaller balance, this can reduce interest over time and may shorten the payoff period. The effect depends on the loan balance, rate, remaining term, amount and timing of extra payments, and how the lender applies them.

For a full schedule, each row commonly lists the payment number or date, starting balance, interest, scheduled principal, extra principal, total paid, and ending balance. The ending balance in one row becomes the starting balance in the next. The final payment may be smaller than the usual payment because only the remaining amount is due.

How to Use the Estimate

• Enter the principal you actually owe or expect to borrow, rather than the amount of a monthly payment.
• Use the APR provided in the lender’s disclosure. The calculator treats it as a fixed annual rate and converts it to a monthly rate.
• Enter the original term in years and the extra amount you intend to add to principal each month. Enter zero to model scheduled payments only.
• Compare the displayed 12-month balance with the starting balance to see the estimated principal reduction over that period.
• For a full payoff date or a month-by-month ledger, use a schedule tool that calculates each payment row and adjusts the final payment.

Extra payments are not always automatically treated as principal reduction. Payment instructions and servicing procedures vary, and a lender may handle an amount beyond the scheduled payment differently. Check the loan statement or ask the servicer how to designate extra principal, whether an extra amount changes the next due date, and whether the contract has any relevant restrictions or charges. This calculator does not model those terms.

Common Mistakes and Limits

A frequent mistake is treating the extra amount as part of the required payment. It is an optional additional amount in this estimate; the scheduled payment is calculated separately. Another is entering a monthly interest rate as the APR. If the quoted rate is annual, enter that annual percentage: the formula divides it by 12 for monthly calculations.

Rounding also matters. The scheduled payment is rounded to cents, but lender calculations may use more precise daily accrual, different posting dates, or payment allocation rules. The displayed interest-without-extras figure is a simplified total based on the rounded payment and the full original term; it does not calculate the revised total interest or exact payoff month under extra payments. The 12-month balance is not a complete amortization schedule.

For a variable-rate loan, a changing payment, skipped or late payment, lump-sum extra payment, or an irregular payment date, a fixed-rate monthly estimate will not reproduce the actual account. A detailed calculation needs the applicable rate and payment history for each period, along with the lender’s balance and interest conventions.

Frequently Asked Questions

Is there a free amortization schedule with extra payments? This calculator is a free estimate of the scheduled payment, interest without extra payments, and balance after 12 months with a recurring extra principal amount. For a complete payment-by-payment schedule, use a tool that lists each period and updates the final payment.

Does an extra payment go straight to principal? Not necessarily. The result assumes it does. Confirm the lender’s payment-allocation process and use any available instruction for extra principal if that is how you intend the payment to be applied.

Does paying extra reduce the monthly payment? This estimate keeps the scheduled payment unchanged and treats the extra amount as additional principal. Whether a lender recalculates a required payment after a principal reduction depends on the loan and its servicing terms.

How do I calculate the interest saved by extra payments? Compare total interest from a schedule with extra payments against a schedule using the same loan inputs and no extras. This calculator shows the no-extra interest estimate, but does not calculate the extra-payment schedule’s final interest or exact payoff month.

Can I use this for a variable-rate loan? Only as a fixed-rate snapshot. A variable rate can change the interest charged and payment schedule, so an estimate using one APR cannot predict later balances accurately.

This result is an estimate; the lender’s disclosure gives the exact figures.

Related

• Amortization Calculator With Extra Monthly Payments
• Amortization Calculator Based on Payment
• Biweekly Amortization Calculator: Payment and Interest

in p | Loan amount | $ | 20000 | 1 | 100000000
in apr | Interest rate (APR) | % | 8 | 0.01 | 100
in yrs | Loan term | years | 5 | 0.0833 | 50
in extra | Extra principal per month | $ | 100 | 0 | 100000000
out pmt | Scheduled monthly payment | $ | round(p * (apr / 1200) / (1 - (1 + apr / 1200) ^ -(yrs * 12)), 2) | 2
out nint | Interest without extra payments | $ | pmt * yrs * 12 - p | 2
out bal | Balance after 12 months with extra payments | $ | max(0, p * (1 + apr / 1200) ^ 12 - (pmt + extra) * ((1 + apr / 1200) ^ 12 - 1) / (apr / 1200)) | 2