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Amortization Schedule with Extra Payments

What one extra payment a month actually saves you.

Trever Barney
By Trever Barney
Founder & Writer · About the author · Last reviewed 2026-08-25

This is a real month-by-month simulation, not an approximation. Extra payments change the schedule non-linearly, so the only honest way to compute the saving is to walk the loan forward one month at a time — which is exactly what happens below, and what you can read in the table.

$
%
$
Biweekly adds the equivalent of one extra full payment per year.
Interest saved
—

Minimum payments

Payment—
Payoff—
Total interest—
Total paid—

With extra payments

Payment—
Payoff—
Total interest—
Total paid—
Each month: interest = balance × i · principal = payment − interest · balance −= principal
Enter your numbers to see the math.

Amortization schedule

Year Payment Principal Interest Balance
This calculator produces estimates based on the assumptions you enter. It is not a loan offer, a pre-qualification, or a guarantee of terms. Your actual rate, payment, and costs are determined by a lender and will differ. Confirm with your servicer that extra payments are applied to principal — some apply them to the next scheduled payment instead, which does not shorten the loan.

How amortization actually works

Every month, three things happen in strict order:

interest  = balance × (annual rate ÷ 12)
principal = payment − interest
balance   = balance − principal

That is the entire mechanism. There is no separate "interest schedule" that a lender locks in at closing — the amortization table is simply the output of running those three lines 360 times. This is why prepayments work: they reduce the balance, which reduces every subsequent interest calculation, which means more of every future payment goes to principal.

Why the early years feel like nothing is happening

In month one of a 30-year loan at typical rates, roughly three quarters of your payment is interest. That ratio flips slowly. The crossover point — where more of your payment goes to principal than to interest — usually falls somewhere around year 18 on a 30-year loan.

This is not a trick and it is not front-loading in any sinister sense. It falls directly out of charging interest on an outstanding balance. But it does explain why extra payments made in years 1–5 are worth dramatically more than the same payments made in years 20–25.

The biweekly question, answered plainly

Biweekly payment plans are frequently sold as a clever optimization, sometimes with a setup fee attached. The actual mechanism is simple arithmetic: there are 52 weeks in a year, so paying half your monthly payment every two weeks means 26 half-payments — the equivalent of 13 monthly payments instead of 12.

You do not need to pay anyone to do this. Dividing your payment by 12 and adding that amount to each monthly payment produces the same result. The calculator's biweekly toggle models it exactly that way, which is why the two approaches give identical numbers.

Frequently asked questions

How much does one extra payment a month save?
It depends on the rate and how early you start, but the effect is large because every extra dollar goes straight against principal and removes all future interest on that dollar. On a typical 30-year loan at current rates, an extra $200 a month commonly cuts several years off the term and saves a six-figure sum in interest. Use the calculator above with your own numbers.
Does paying biweekly really work?
Yes, but the mechanism is unglamorous. Paying half your mortgage every two weeks produces 26 half-payments a year, which equals 13 full monthly payments instead of 12. The saving comes entirely from that one extra annual payment, not from any interest-calculation trick. You can get exactly the same result by paying an extra 1/12th of your payment each month.
Should I make extra payments or invest the money?
A prepayment earns a guaranteed, risk-free return equal to your mortgage rate. Investing has a higher expected return but is not guaranteed and is not tax-equivalent for everyone. The higher your rate, the stronger the case for prepaying. This is a genuine trade-off with no universal answer, and it depends on factors this calculator cannot see.
Why do extra payments save more when made early?
Interest each month is charged on the outstanding balance. Early in a loan the balance is at its largest, so a dollar of principal removed then eliminates interest across the longest remaining period. The same dollar paid in year 25 removes only five years of future interest.

Sources

  1. Primary Mortgage Market Survey (PMMS) — Freddie Mac · week ending 2026-08-20 · accessed 2026-08-25 · Source of the default rate
  2. Your Home Loan Toolkit — Consumer Financial Protection Bureau · accessed 2026-08-25
  3. When can I remove private mortgage insurance (PMI) from my loan? — Consumer Financial Protection Bureau · 2023-08-28 · accessed 2026-08-25

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