Principal & Interest
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Mortgage Calculator
Calculate your monthly mortgage payment, total interest, and total cost. See the full amortization schedule — when your payments stop being mostly interest and start being mostly equity.
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Estimated monthly payment (P&I)
Property Tax
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Insurance
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Total Interest
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Total Cost
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20% Equity Date
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Amortization Schedule
| Month | Payment | Principal | Interest | Balance |
|---|
Property tax and insurance are estimates added to the monthly P&I payment. Actual amounts depend on your location and insurer. Consult a mortgage broker for exact figures.
How mortgage amortization works
In the early years of a mortgage, most of your monthly payment goes toward interest — the bank is earning back the risk of lending you a large sum. As the principal balance shrinks, the interest portion of each payment decreases and the principal portion grows. This is why making extra principal payments early in a loan's life has an outsized effect on total interest paid.
The 20% equity date shows when your remaining balance drops to 80% of the original home value — the threshold at which you can typically cancel private mortgage insurance (PMI). If you put down less than 20%, lenders typically require PMI until you reach this point.
How to verify this calculator
- Last verified
- — the calculation logic and the automated regression suite were re-run on this date. Fee and rate fields are editable estimates; confirm current values against the official schedule before relying on them.
- Official / methodology source
- No platform fee schedule applies to this calculator. Its formula is documented in the project source and exercised by the regression suite linked below.
- Method & testing
- All arithmetic runs locally in your browser — no input is uploaded. Calculation behaviour is exercised by the repository's regression suite: 39/39 checks passed (run 2026-11-08). Source & tests on GitHub.
- Maintained by
- Jim (Maoming, Guangdong, China) · eyetoolkit. Report a wrong result through the contact page.
- Changelog
- 2026-11-08 — Added this verification panel (last verified date, official or methodology source, test coverage, named maintainer, changelog). Calculator logic and default rates are unchanged.