Mortgage calculator
On a typical 30-year mortgage, you will usually pay the bank more in interest than you originally borrowed. The exact amount depends on your rate and loan size—use the calculator above to see your numbers.
API example
Same result via GET request (use current inputs above):
curl -s "https://howdeedo.com/api/calc/mortgage?homePrice=350000&downPayment=70000&downPaymentMode=amount&annualRatePct=6.5&termYears=30&propertyTaxAnnual=4200&insuranceAnnual=1800&hoaMonthly=150&solveFor=payment&includeSchedule=false"fetch("https://howdeedo.com/api/calc/mortgage?homePrice=350000&downPayment=70000&downPaymentMode=amount&annualRatePct=6.5&termYears=30&propertyTaxAnnual=4200&insuranceAnnual=1800&hoaMonthly=150&solveFor=payment&includeSchedule=false").then(r => r.json())Good to know
The biweekly trick. Pay every two weeks instead of once a month and you make 26 half-payments a year—that is 13 full payments instead of 12. That one extra payment per year knocks years off the loan and saves a substantial amount in interest. Same money, different calendar.
Interest is wildly front-loaded. In year one of a 30-year mortgage, about 70% of each payment is interest. By year 20, it flips and most of the payment finally goes to principal. Your payment does not change, but where it goes changes completely.
Rate shopping has real math behind it. Half a point in rate can mean tens of thousands of dollars over 30 years—roughly the price of a decent used car. Three quotes, three phone calls, one afternoon.
Methodology
fixed-rate-amortization — Monthly payment = P * [r(1+r)^n] / [(1+r)^n - 1], with a zero-rate branch of principal divided by number of payments.
Assumptions
- Fixed-rate, fully amortizing loan.
- Monthly compounding and monthly payments.
- Property tax, insurance, and HOA are added to all-in monthly cost only and do not change amortization.
- PMI, points, and closing costs are excluded.
Calculation version: 0.1.0
References
Disclaimers & sources
Not financial advice. This is an estimate for comparison purposes.