Mortgage & Payoff Calculator: The True Cost of Your Home Loan

When Marcus and his wife signed their 30-year mortgage, the only number either of them really looked at was the monthly payment — it took a decade before they added up how much of every check was going toward interest, not the house. Ask most homeowners what their mortgage “really” costs and they’ll tell you the monthly payment. That’s only half the picture. Over a 30-year loan, interest can add up to more than the amount you originally borrowed — and a small extra payment made early does more work than the same amount made later.

What the calculator actually shows you

Beyond the standard monthly payment, it breaks down exactly how much of each payment goes to interest versus principal over time, and what happens if you add extra payments — occasional or recurring — toward the principal.

A $400,000 loan at 6.5% over 30 years runs about $2,398 a month — and over the full term, total interest paid can exceed $460,000. That’s the number most people never actually look up before signing.

Why early extra payments punch above their weight

In the early years of a mortgage, most of each payment is interest, not principal — the amortization schedule is front-loaded that way by design. An extra $200/month applied in year 2 knocks years off the loan and saves far more interest than the same $200/month applied in year 25, when most of the payment is already going to principal anyway.

The refinance trap

A lower monthly payment from refinancing can look like a win while quietly resetting your amortization clock — years 1-5 of interest-heavy payments start over, even if the new rate is better. Always compare total interest over the remaining term, not just the new monthly figure, before refinancing.

Rent vs mortgage isn’t really the comparison

The honest comparison isn’t “rent vs mortgage payment” — it’s rent vs (mortgage payment + property tax + insurance + maintenance) minus (equity built + any appreciation). Most online comparisons quietly drop half of those terms.

Should I pay off my mortgage early if I have a low rate?

If your rate is below what you could reasonably earn investing the same money, extra payments toward the mortgage usually aren’t the mathematically optimal move — though the guaranteed, risk-free “return” of eliminating debt still has real value for many people.

Does a 15-year mortgage always beat a 30-year one?

It saves substantial interest, but at a materially higher monthly payment. A 30-year loan with voluntary extra payments gives you the same payoff-speed option without the binding higher minimum payment.

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Disclaimer: This article is for general information only and is not financial or tax advice. Consult a qualified advisor before making investment or tax decisions.