Mortgage Calculator
It converts a home price, down payment, interest rate and term into a fixed monthly payment, the total interest you will pay, and a full amortization schedule.
Estimated monthly payment
$2,742.11
Loan amount
$360,000
Total interest
$459,160
Total repaid
$819,160
Payments
360
Down %
20.0%
Payoff year
2056
What it calculates
It converts a home price, down payment, interest rate and term into a fixed monthly payment, the total interest you will pay, and a full amortization schedule.
Why it matters
Interest is the largest single cost of home ownership. A rate difference of half a percentage point can change lifetime interest by tens of thousands.
Who it's for
First-time buyers comparing offers, homeowners considering a refinance, and anyone stress-testing affordability before making an offer.
Formula
- P
- Principal — home price minus down payment
- r
- Monthly interest rate (annual rate ÷ 12)
- n
- Total number of monthly payments (years × 12)
- M
- Monthly payment of principal and interest
Worked example
$450,000 home, 20% down, 6.5% over 30 years
- 1Principal P = 450,000 − 90,000 = 360,000
- 2Monthly rate r = 6.5% ÷ 12 = 0.005417
- 3Payments n = 30 × 12 = 360
- 4M = P · r(1+r)ⁿ / ((1+r)ⁿ − 1)
Monthly payment ≈ $2,275, total interest ≈ $459,160
How the mortgage calculator works
A repayment mortgage is an annuity. Each payment is identical, but the split changes: early payments are mostly interest because interest is charged on a large outstanding balance, and later payments are mostly principal. The amortization table shows that crossover point.
P is the loan principal after your down payment, r is the monthly interest rate (annual rate ÷ 12 ÷ 100) and n is the total number of monthly payments (years × 12).
Property tax and insurance are not part of the loan formula — they are escrowed alongside it, so we add them to your total monthly outflow separately.
Common mistakes
- Budgeting only for principal and interest — property tax, insurance and any HOA dues are extra.
- Comparing a 15-year quote against a 30-year quote on monthly cost alone.
- Assuming an introductory fixed rate applies for the whole term.
Tips and best practice
- Overpay early: a payment in year one removes far more interest than the same payment in year twenty.
- Shortening the term usually beats overpaying occasionally, if your budget can absorb it.
- Compare the total cost over the fixed period, including closing costs, not just the headline rate.
Frequently asked questions
How is a monthly mortgage payment calculated?
With the annuity formula M = P · r(1+r)ⁿ / ((1+r)ⁿ − 1), where P is the loan amount, r the monthly interest rate and n the number of monthly payments.
Does this calculator include taxes and insurance?
It calculates principal and interest. Add property tax, homeowners insurance and any HOA dues separately to get a true monthly cost.
How much of a down payment do I need?
Most lenders want at least 3–5%, but 20% down avoids private mortgage insurance and typically unlocks materially better rates by lowering the loan-to-value ratio.
Should I choose a shorter term?
A shorter term raises the monthly payment but cuts total interest sharply. Compare both in the calculator before deciding.
What does overpaying actually save?
Overpayments reduce the outstanding balance immediately, so all future interest is charged on a smaller amount. Early overpayments save the most.
Is the result a mortgage offer?
No. It is an estimate for planning. Lenders apply their own affordability, credit and valuation rules.
Related calculators
Further reading
Methodology & trust
- Formula source
- Standard annuity (amortizing loan) formula.
- Last updated
- 2026-07-28
- Privacy
- Every calculation runs in your browser. No inputs are sent to a server or stored.
- Accessibility
- Keyboard navigable, labeled inputs and WCAG AA color contrast.