What One Extra Mortgage Payment a Year Really Saves

"Make one extra mortgage payment a year and knock years off your loan" is one of the few pieces of folk financial advice that survives contact with a spreadsheet. It works, the savings are real, and the mechanism is simple enough to explain in a paragraph. It's also oversold in a few specific ways, and there's one servicer trap that can quietly void the whole exercise. Numbers first, caveats after — and our extra payment calculator will run your loan while you read.

Why extra dollars punch above their weight

Your regular mortgage payment is split between interest and principal by the amortization schedule, and early on the split is ugly — in year one of a 30-year loan at today's rates, roughly three-quarters of each payment is interest. But any extra dollar you send skips that split entirely and goes 100% to principal. A smaller principal balance means every subsequent month accrues less interest, which means more of every future regular payment goes to principal, which shrinks the balance faster still. One extra dollar today quietly discounts every one of the hundreds of payments behind it. That's the entire trick.

The actual numbers

Take a $320,000 loan at 6.5% for 30 years. The monthly payment is $2,022.62 (principal and interest — taxes and insurance ride on top and don't participate in any of this). One extra payment a year, spread out monthly, is about $169 extra per month.

Result: the loan pays off roughly 5–6 years early, and total interest drops by roughly $90,000 — on a loan that would otherwise charge about $408,000 in interest over its full life. Treat those as approximations, not gospel: the exact savings depend on your balance, rate, and how early in the loan you start (extra payments in year 2 do far more work than the same dollars in year 22). Put your own numbers into the extra payment calculator and get your own answer — it takes about a minute.

The biweekly-payment "trick," honestly

You'll see biweekly payment plans marketed as a clever hack: pay half your mortgage every two weeks instead of the full amount monthly. The math is just calendar arithmetic — there are 26 two-week periods in a year, so 26 half-payments equal 13 full payments. It's exactly the one-extra-payment-a-year strategy wearing a costume. There is nothing wrong with it, except that some servicers and third-party companies charge setup or per-payment fees for the privilege of this arithmetic. Don't pay anyone for it. The DIY version: divide your monthly payment by 12, add that amount to each month's payment as extra principal, done. Same 13th payment, zero fees, no middleman.

The servicer trap

When you send extra money, confirm your servicer applies it to principal — not to "next month's payment." Many servicers default to treating extra funds as an early payment of the following month, which advances your due date and saves you nothing at all. Most payment portals have an "apply to principal" option; if you pay by check, write "apply to principal" on the memo line, then verify on your next statement that the balance actually dropped by the extra amount. This single misapplied setting is the difference between the numbers above and zero.

Prepay or invest? The honest trade-off

Every extra dollar sent to the mortgage is a dollar not invested, so the comparison is simple to state and impossible to settle universally. Prepaying earns you a guaranteed return equal to your mortgage rate — 6.5% in our example, tax questions aside, with zero market risk. Investing offers an expected return that has historically been higher over long periods, but it arrives with volatility and no guarantee, as anyone who started investing in 2008 can narrate. There's also a liquidity asymmetry people skip past: money in a brokerage account can be sold on a bad day; money in your walls cannot — extra principal doesn't come back out without selling or borrowing against the house. Run both paths — the extra payment calculator for prepaying, the savings growth calculator for investing — and notice that at a 6.5% mortgage rate the race is close enough that temperament is a legitimate tiebreaker. At a 3% rate, the math leans the other way.

One tax footnote that used to complicate this comparison and mostly no longer does: the mortgage interest deduction only helps if you itemize, and since the standard deduction roughly doubled in 2018, most households don't. For them, prepaying saves interest at the full sticker rate — no "but the deduction" asterisk required. If you do itemize, your effective mortgage rate is somewhat lower and the invest side of the ledger gets a small thumb on the scale.

Prepayment penalties

Rare on modern conforming loans — regulations after 2008 sharply limited them — but "rare" is not "never," especially on non-qualified or older mortgages. Check your loan documents for a prepayment penalty clause before starting, or ask your servicer directly. The CFPB's Ask CFPB library explains what's allowed and where penalties still show up.

When prepaying is the wrong move

• You're carrying credit card debt. Prepaying a 6.5% loan while paying 24% on a card is choosing the small fire over the large one. Kill the card first — the payoff calculator shows the timeline, and avalanche vs. snowball covers the order of attack.
• You have no emergency fund. Extra principal is illiquid; a surprise $3,000 repair with no cushion lands on a credit card, converting your 6.5% savings into 24% debt. Fund the cushion first — the emergency fund calculator sizes it.
• You're skipping a 401(k) match to do it. A 50–100% guaranteed match beats a 6.5% guaranteed prepayment, every time.

Common questions

Does an extra payment lower my monthly bill?

No. Your required payment stays exactly the same; what changes is the end date — the loan simply runs out of balance years early. The exception is a recast: after a large lump-sum principal payment, some servicers will re-amortize the remaining balance over the original term, lowering the monthly payment instead of shortening the loan, usually for a small fee. Ask your servicer if that's the outcome you actually want.

Is a lump sum better than monthly extras?

Dollars applied to principal earlier save more interest, so a lump sum in January beats the same total dribbled out through December — but the difference is modest, and the monthly habit wins in practice because it actually happens. If you get a windfall, apply it when it arrives (marked "principal"). Otherwise, automate the monthly extra and stop thinking about it.

Should I pay off the mortgage before retiring?

Entering retirement without a mortgage payment lowers the income your savings must produce every month, which is why many people target payoff at retirement age — and why the peace of mind is worth real money to some. But draining investment accounts to do it, or skimping on retirement contributions to prepay a low-rate loan, can leave you house-rich and cash-poor at exactly the wrong time. It's a genuine trade-off between a guaranteed expense reduction and portfolio flexibility, not a moral test. Run your numbers both ways before deciding.

This article is general information, not personalized financial advice. How we write and review articles is covered in the editorial note on our About page.