Calculator Tools

Mortgage Extra Payment Calculator

See how much interest and time you save with extra mortgage payments. Combine extra principal, biweekly, and a lump sum, then compare savings.

Currency

Pick a currency for display. The math is the same in every currency.

Loan basics

Start with the loan you have or are considering. Numbers here drive the baseline payment.

Loan amount

Term (years)

Interest rate (%)

Extra payments

Combine any of the three strategies. The result panel shows the savings versus paying only the standard amount.

Extra principal each month

A fixed dollar amount added to every monthly payment, applied directly to principal.

Biweekly acceleratedPay half the monthly payment every two weeks. Twenty-six half-payments per year equals one extra full payment per year.

One-time lump sum

Applied at month

Set the lump sum to 0 to skip this strategy. Month 1 applies the lump sum with the first payment.

Result

All math runs in your browser. Loan amounts, rates, and prepayment amounts never leave your device.

Interest saved

$108,097

Lifetime interest you avoid versus the standard 30-year payoff.

Months saved

Equal to 6 yr 2 mo off the original schedule.

New payoff

23 yr 10 mo

About 23.8 years from the first payment.

Baseline (standard payments only)

Monthly payment: $2,212.24

Payoff: 30 yr

Total interest: $446,406

Total of all payments: $796,406

With your extra payments

Effective extra per month: $200

Payoff: 23 yr 10 mo

Total interest: $338,309

Total of all payments: $688,309

Worked examples

Tap any preset to load realistic numbers and see the savings for that scenario.

How the math works

Standard payment: the fixed monthly amount that fully amortizes the original loan over the original term, using M = P r (1 + r)^n divided by ((1 + r)^n minus 1).
Extra principal: a fixed dollar amount added to every monthly payment and applied directly to the principal balance.
Biweekly accelerated: modeled as one extra full monthly payment per year, the same way lenders handle biweekly schedules at monthly granularity.
Lump sum: applied in full at the month you choose. The remaining schedule continues at the standard payment with any recurring extras still in effect.
Savings: the difference between the baseline schedule (no extra payments) and the accelerated schedule, in months and in total interest paid.

What to watch out for

Confirm with your servicer that extra payments are applied to principal rather than next month's interest. Most accept a memo-line note such as "apply to principal".
Check for prepayment penalties. Most modern fixed-rate mortgages have none, but it is worth confirming on the note before committing to a strategy.
True biweekly programs often charge an enrollment fee. You can get the same effect by sending one extra full payment per year on your own.
Property taxes, homeowners insurance, PMI, and HOA dues are not included here. This tool only models principal and interest.
The numbers above are estimates based on the inputs you provide and standard fixed-rate amortization math. This is not financial advice.

How to use

Enter the loan amount, the term in years, and the interest rate, or tap a preset to load realistic numbers.
Add any combination of extra payments: a fixed extra principal each month, biweekly accelerated, and a one-time lump sum at the month of your choice.
Read the headline cards for interest saved, months saved, and the new payoff date versus the standard schedule.
Compare the baseline schedule and the accelerated schedule side by side for monthly payment, total interest, and total of all payments.
Click Show year-by-year schedule to see how the loan amortizes year by year with your extra payments applied.
Click Copy plan summary to paste a plain-text version of the plan into your notes, budget, or shared document.

About this tool

Mortgage Extra Payment Calculator answers the single question every borrower asks before adding extra principal to a mortgage: how much time and how much interest will I actually save. Set the loan amount, the term in years, and the interest rate, then layer on any combination of three common prepayment strategies. Add a fixed extra dollar amount to every monthly payment, switch on biweekly accelerated payments (the standard way lenders model this, equivalent to one extra full monthly payment per year), and schedule a one-time lump sum at the month you choose. The calculator runs two full month-by-month amortization simulations, one for the standard schedule and one with your extra payments, and shows the savings side by side: interest saved, months saved, the new payoff date in years and months, and the full year-by-year schedule with interest paid, principal paid, extra paid, and the running balance. Six realistic presets cover the most common cases people search for: rounding up by 100 a month, adding 200 a month to principal, biweekly accelerated, putting an annual tax refund toward principal as a lump sum, paying a 30-year loan off in 15 years with aggressive extra principal, and a combined strategy that stacks all three. Supports US dollar, euro, British pound, Canadian dollar, Australian dollar, Indian rupee, and Turkish lira from a dropdown for international borrowers. Math is the standard fixed-rate amortization formula and a transparent month-by-month simulation; everything runs in your browser, so loan amounts, rates, and prepayment amounts never leave your device. Useful for choosing between strategies, sizing an affordable extra payment, deciding whether a lender's biweekly program is worth its enrollment fee, planning what to do with a bonus or tax refund, and seeing exactly how many years and how many dollars a small recurring extra principal payment will save over the life of the loan.

Free to use. Works in your browser. No signup, no login.

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