Mortgage Amortization Calculator with Extra Payments
Build a yearly amortization table, compare a monthly extra with a 13-payment budget, and see the payoff date, total interest and the true final payment.
What This Calculator Does
See how a fixed-rate mortgage plays out from the principal you start with, across every month of the term you select. Each month adds interest to the balance; when the month closes, your scheduled P&I is credited, together with whatever extra principal you put in. Picking 13-payment spreads a yearly budget into an approximate monthly amount, which is not the same as reproducing how a true biweekly plan would post. Results include a full financial summary and a table broken out by year through the final payment.
Who Is This For
It's built for comparing hypothetical monthly P&I schedules in U.S. dollars, including what extra principal changes. Already paying a loan? Enter the balance and remaining term that match your statement, because the tool won't rebuild the payments you've already made.
How It Works
Begin with the principal and a fixed nominal annual rate, then choose the full term and a payment method. In extra-monthly mode, enter the amount even when it's 0. Blank fields and sample numbers aren't your confirmed loan terms. Check planned versus actual final cash, how much you save compared with no extra, and each yearly row. Confirm separately how payments really post and what the payoff steps are.
Frequently Asked Questions
What does the projection calculate?
It shows your scheduled monthly P&I, your chosen extra budget and the cash you'd plan to send each month, when the loan ends and how much the last payment really is. It totals interest and payments and shows the savings against no extra and the extra principal actually used, with every annual row through payoff. It starts from the debt you enter, over the full term you select; past payments, statement balances, fees and loan approval aren't estimated.
Is the 13-payment option a true biweekly plan?
No. Each month the tool adds extra principal equal to the scheduled P&I divided by 12, so a year's budget equals 13 scheduled payments. Paying 26 half-payments lands on the same 13. That match doesn't prove real 14-day pay dates, how a lender credits partial payments, or daily interest. If you pay the same yearly extra at year-end instead, payoff and interest may come out different.
Is extra principal part of the scheduled payment?
No. The scheduled monthly payment is P&I alone, and the extra budget, typed by you or derived by the tool, sits apart. Add them and you get the planned monthly cash, and they post together at month-end. Your last payment can come in below that figure. The monthly-equivalent extra may carry fractions of a cent, and in-between values aren't rounded.
Could extra principal push the last payment past what's owed?
No. In the final month, the cash paid stops at the remaining principal plus that month's interest, and the schedule closes there. Any budget left over isn't counted as paid. Total extra applied is only the cash actually used above scheduled P&I, not the extra you asked for times the number of payments. Yearly principal already includes that used extra, so don't add it on top again.
Why might this projection differ from my bank's amortization statement?
Rounding, dates and payment rules can differ. Only the numbers on screen are rounded; the monthly calculations underneath, covering payment, balance and interest, stay exact. A bank might round each charge to the cent, rely on different dates or apply its own partial-payment rules. A leftover balance smaller than half a cent isn't forgiven. The cents shown say nothing about how a lender will actually bill. To close the loan, ask your servicer for a payoff quote.
Can I use a rate of zero or an extra of zero?
Yes. A 0% rate works as a what-if, but it isn't a loan offer you can actually get. Extra-monthly mode accepts $0, which produces the same schedule as no extra. A blank field is read as unknown rather than zero. Neither the standard mode nor the monthly-equivalent mode adds a hidden extra. Terms run 10, 15, 20, 25 and 30 years, and those choices don't reflect any lender's eligibility rules.
What do the interest savings and yearly rows count?
Savings compare your plan with no extra on the same starting principal, rate and term. They measure nominal modeled interest and months, not an investment return or proof of the lowest total cost. Yearly principal includes extra, interest is listed separately, and any final partial year is kept. You'll find the full yearly schedule in the result and in the PDF. The AI briefing receives the entire 11-metric financial summary and every yearly row.
What should I confirm with my loan servicer?
Confirm your note rate, opening balance and term with your servicer. Then ask how extra principal is applied, when payments post and whether a prepayment penalty applies. CFPB servicing guidance (checked September 30, 2026) says a partial payment may be held until the full amount arrives. It doesn't verify your rate or forecast any specific biweekly plan. Escrow, property taxes, insurance, HOA dues and fees are all left out of the math. To close the loan, you'll need a real payoff quote.