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Mortgage & refinance calculator

Monthly payment, total interest over the life of the loan, and what an extra payment each month actually saves you.

$
$
20% of the price
%
$
Applied straight to principal.
$ /mo
Principal & interest — The loan payment alone
Full monthly cost — Including taxes, insurance and extra
Remaining balance Interest paid to date
Loan amount—
Total interest over the loan—
Total paid (principal + interest)—
Payoff time—
Saved by paying extra—
The number that surprises people

On a 30-year loan at 6.5%, total interest is usually more than the amount borrowed. You are not buying a house at the sticker price — check the "total paid" row before you decide what you can afford.

How this is calculated

  • Standard amortisation: M = P · m / (1 − (1+m)−n), with m the monthly rate and n the number of payments.
  • Extra payments are applied to principal immediately each month, shortening the term rather than reducing the payment.
  • Taxes and insurance are passed through as a flat monthly figure — they are not amortised and not escalated over time.
  • PMI, HOA dues, closing costs and points are not modelled. Add them to the taxes field if you want them in the monthly total.

Should you pay extra or invest the difference?

Paying down a mortgage is a guaranteed, risk-free, tax-free return equal to your interest rate. Investing the same money has a higher expected return but no guarantee. The honest comparison is not "6.5% versus 10%" — it is "6.5% certain versus a range that includes losing money for a decade."

Two practical points. If you itemise and deduct mortgage interest, your effective rate is lower than the headline, which tilts the maths toward investing. And if you have not yet captured an employer retirement match, that comes first: a match is an immediate return no mortgage rate can beat.

Common questions

How much of my mortgage payment goes to interest?

At the start, most of it. On a 30-year loan at 6.5%, roughly three quarters of the first payment is interest and only a quarter reduces the balance. The mix flips gradually; the crossover point on a 30-year loan typically falls around year eighteen.

Does paying extra each month actually help?

Yes, and disproportionately early in the loan, because every extra dollar of principal removes all the future interest that dollar would have accrued. Enter an amount in the extra payment field to see the interest saved and how much sooner the loan clears.

What is not included in this calculator?

PMI, HOA dues, closing costs, discount points, and any escrow adjustment over time. Property tax and insurance are treated as a flat monthly figure that never rises, which in reality it does.

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