This early mortgage payoff calculator shows exactly what happens when you pay more than your required mortgage payment: your new payoff date, the years you cut off the loan, and — the number that usually surprises people — the total interest you never have to pay. Enter your remaining balance, rate, and monthly principal-and-interest payment, then test an extra monthly amount, a one-time lump sum, a biweekly payment schedule, or any combination of the three.

Because mortgage balances are large and terms run decades, early-payoff math is dramatic. On a $300,000 balance at 6.5% with a $2,100/month P&I payment, adding just $200/month pays the mortgage off roughly 4 years sooner and saves over $70,000 in interest. That's not a trick of compounding in the bank's favor — it's compounding flipped to work in yours: every extra dollar retires principal today, which means less interest accrues next month, which means even more of next month's payment hits principal.

The calculator starts from your current balance rather than the original loan amount, so it works whether you closed last month or fifteen years ago. If you're weighing a lump sum, also compare a mortgage recast — recasting lowers your required payment instead of shortening the term, which suits different goals. And if your rate is high, run the Refinance Analyzer first: a lower rate plus extra payments beats extra payments alone.

The calculator runs a month-by-month amortization simulation twice — once at your current payment, once with your accelerated plan — and reports the difference:

Biweekly mode uses the standard industry approximation: 26 half-payments per year equal 13 full payments instead of 12, so the effective monthly payment is your payment × 13 ÷ 12. That single "invisible" extra payment per year typically cuts 5–6 years off a fresh 30-year mortgage on its own.

Worked example — $300,000 at 6.5%, $2,100/month P&I:

• Current plan: paid off in about 25 years with roughly $330,000 of total interest.
• +$200/month: paid off in about 21 years — interest drops by roughly $70,000.
• Biweekly instead: similar effect to adding ~$175/month, about 3–4 years saved.
• +$200/month and a $10,000 lump sum: paid off in about 20 years, well over $85,000 of interest avoided.

One important input note: enter principal and interest only. Your total monthly bill likely includes escrow for property taxes and homeowner's insurance — those continue regardless of your loan balance and don't belong in payoff math. If you're not sure how your payment splits, your mortgage statement itemizes it, or you can rebuild the P&I figure with our Advanced Mortgage Calculator.

• Extra monthly payment. The simplest and most flexible: it's voluntary, so you can pause it in a tight month. Make sure your servicer applies it to principal — the CFPB advises confirming in writing that extra funds go to principal rather than being held as an "advance" on next month's bill.
• Biweekly payments. Great if you're paid every two weeks — the extra annual payment happens without feeling it. Skip third-party "biweekly conversion services" that charge setup fees; you can replicate the effect free by adding one-twelfth of your payment to each monthly bill.
• Annual lump sums. Tax refunds, bonuses, and RSU vests aimed at principal early in the loan's life have the largest effect, because early-loan balances are highest and interest accrual is steepest.
• Round-up habit. Rounding a $2,087 payment to $2,200 feels painless but compounds into years of savings over a full term.

Two checks before you accelerate. First, prepayment penalties: under the Dodd-Frank rules the CFPB enforces, penalties on most new mortgages are heavily restricted and phase out within three years — but check your closing documents if your loan predates 2014 or is non-qualified. Second, opportunity cost: if your rate is 3%, extra payments "earn" a guaranteed 3% return, which may trail what a diversified portfolio or even a high-yield savings account pays — our mortgage payoff savings guide works through the invest-vs-prepay tradeoff with real numbers, and the Interest Calculator lets you model the investing side yourself.

Only if you itemize. Since the standard deduction roughly doubled, the IRS reports that most taxpayers no longer itemize, which means most homeowners get zero tax benefit from mortgage interest — making early payoff strictly better for them. If you do itemize, IRS Publication 936 covers the home mortgage interest deduction limits; remember a deduction only refunds your marginal tax rate on each interest dollar. Paying $10,000 of interest to save $2,400 in tax is still $7,600 out the door.