Mortgage Payoff Calculator
Enter your balance and current payment, then add an extra monthly amount: the calculator shows the new payoff date and the exact interest the extra payment saves you.
The extra-payment lever, measured exactly
Advice about paying a mortgage early is usually long on feeling and short on figures. This calculator replaces the feeling: at your current payment the loan ends on a specific month with a specific interest bill; add an extra amount and both change by amounts you can weigh against other uses of the money.
Each month: balance grows by balance × rate ÷ 12, then your payment (plus extra) comes off
Example pattern: a $20,000 balance at 6% paid at $400 a month takes 58 payments and $3,072.27 of interest. At $500 a month it takes 45 payments and $2,370.33 — the extra $100 saves $701.94 and 13 months. (The same simulation runs your mortgage below.)
When paying early is the wrong move
The interest saved is guaranteed, which is the case for doing it. The cases against: emptying your emergency fund to do it, skipping an employer retirement match that beats the rate, or carrying card debt at 24% while prepaying a mortgage at 6%. Order matters more than enthusiasm.
How this is calculated
A month-by-month simulation, not a formula shortcut: each month the balance accrues interest at the nominal rate ÷ 12, then your payment plus the extra is applied, with the final payment trimmed to the exact remainder. The baseline run uses your current payment alone; the comparison run adds the extra. If the current payment does not exceed the first month's interest, the page says so — the loan would never amortize.
Frequently asked questions
Should I tell my lender the extra is for principal?
Yes — always. Extra money sent without instruction can be applied to future payments (prepaying interest scheduling) instead of principal. Mark it 'apply to principal' and check the next statement.
Is it better to pay extra monthly or one lump sum yearly?
Monthly wins by a small margin because principal falls sooner, so less interest accrues in between. The difference is minor next to the decision to pay extra at all.
Does paying extra change my required payment?
No. The contractual payment is unchanged; you simply reach a zero balance earlier. If you need the lower payment itself, that is a refinance or a recast, not extra payments.
What about the tax deduction on mortgage interest?
Paying less interest means deducting less — but a dollar of interest saved is worth more than the fraction of a dollar the deduction returned. Never pay $1 of interest to save 25¢ of tax.
Embed this calculator
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CalcPrincipal