Extra Mortgage Payment Calculator

Each period the extra is added to the principal portion, so the balance falls faster and every later month’s interest is charged on less. The payment stays the same and the term shortens (the US default). Years saved and interest saved are measured against the same loan with no extra.

Why a small extra does so much

On a mortgage, interest is charged on the outstanding balance, and that balance is highest at the start — so the early years are mostly interest. Anything you pay above the scheduled amount skips straight to principal, permanently lowering the balance every future month’s interest is calculated on. The effect compounds: each extra dollar saves not just its own interest but the interest on the interest it would have generated, for the rest of the loan. That is why a payment that feels small — an extra hundred or two a month — can erase years from the term and tens of thousands in interest.

This calculator keeps your payment the same and shortens the term, which is how US mortgages treat extra payments by default. Enter a recurring extra, an annual bonus or a one-time lump (or all three) and it shows the years saved, the interest saved, the new payoff date and the effective new term — measured against the identical loan with no extra.

Worked example — a $300,000 loan at 6.5% over 30 years (payment ~$1,896): Add $200 a month and the loan clears in about 23 years instead of 30 — nearly 7 years early — saving roughly $103,000 in interest. The earlier you start, the more you save: the same $200 begun in year five saves noticeably less.

Compare amounts — and round up painlessly

How much extra is worth it? The calculator lays out the payoff at several common amounts — an extra 100, 250 and 500 a month — alongside your own, so you can see the trade-off rather than guess. The relationship is not quite linear: doubling the extra more than doubles the early-year impact, because larger payments knock down the high-interest balance faster. Use the comparison to find an amount that is both affordable and effective.

If committing to a fixed extra feels daunting, try the round-up option: it rounds your payment up to the next 100 and puts the difference on principal. It is barely noticeable month to month but still trims the term, and it is an easy habit to start. Any of these levers — recurring, annual, one-time or round-up — can be combined.

Faster equity, sooner PMI drop-off

Extra payments do more than save interest — they build equity faster, which matters if you pay private mortgage insurance. PMI comes off once your balance falls to 80% of the home’s value, and prepaying gets you there sooner. Enter your home’s value and the calculator shows how much earlier the extra payments drop PMI, a saving on top of the interest. It is one of the most overlooked benefits of prepaying early in a loan.

The chart shows two balance curves — with and without your extra — starting together and diverging as the extra-payment line dives below. The horizontal gap is the time you save; the area between them is, roughly, the interest. If you are already partway through your mortgage, enter your current balance and remaining term to see what starting extra payments now would do from here.