🏠 Mortgage Calculator
Estimate monthly principal and interest for a fixed-rate home loan. Runs privately in your browser.
Principal, interest, and what is missing
A mortgage payment has two core parts: principal (paying back what you borrowed) and interest (the lender's charge for lending). This calculator computes the principal-and-interest portion using the standard amortisation formula. What it deliberately excludes — property taxes, homeowners insurance, HOA dues and, where relevant, mortgage insurance — varies enormously by location, so including them would produce a false sense of precision.
Because the loan amount is the price minus the down payment, your down payment does double duty: it lowers what you borrow and, at common thresholds like 20% in the US, can remove mortgage insurance from the picture entirely. Run the numbers at different down payments to see the break points.
How the payment is derived
The payment formula is M = P × r × (1 + r)^n / ((1 + r)^n − 1), where P = home price − down payment, r = annual rate ÷ 12, and n = years × 12. At a 0% rate the payment is just P ÷ n.
A 350,000 home with 70,000 down
A 350,000 home with a 70,000 down payment means borrowing 280,000. At 6.5% for 30 years the monthly rate is about 0.5417% over 360 payments, giving roughly 1,769.79 per month for principal and interest. Over 30 years that is about 637,000 in total payments — nearly 357,000 of it interest. Dropping the rate to 6.0% brings the payment to about 1,678.74 and saves roughly 32,800 over the full term, which is why shopping lenders matters.
Why this is not your true monthly cost
- Treating the result as your true monthly cost. Add estimated property tax, insurance and HOA fees separately — together they often add 25–50% to the P&I payment.
- Forgetting closing costs. Typically 2–5% of the loan, due upfront, and not part of this calculation.
- Assuming the quoted APR is the payment rate. The payment is based on the note rate; APR includes fees and is used for comparison, not amortisation.
- Testing only one rate. Compare 6.25%, 6.5% and 6.75% — small rate differences compound into large lifetime totals.
Mortgage questions
Does this include taxes and insurance?
No — it shows principal and interest only. Escrowed taxes, homeowners insurance and HOA fees must be added separately to get your full housing payment.
How much down payment do I need?
Conventionally 20% avoids mortgage insurance in the US, but many loans accept far less. Try several values here and note how the borrowed amount and payment change.
30-year or 15-year term?
A 15-year loan has a higher monthly payment but a much lower rate and far less total interest. Compare both terms here and check the total-payment line, not just the monthly figure.
Is the payment the same every month?
For a fixed-rate mortgage, yes — the total P&I payment is constant, but its split between interest and principal shifts over time. Early payments are mostly interest.
Why is my bank's estimate higher?
Banks usually quote a full escrowed payment including taxes and insurance, and may add PMI if your down payment is under 20%. Match inputs carefully before comparing.
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Tip: double-check inputs before relying on results for important decisions.
About
Principal and interest only. Real payments often include taxes, insurance, and HOA.