How to use this calculator
Enter the home price and your planned down payment — the difference is your loan amount. Set the interest rate from an actual lender quote (or the current national average if you're early in the process), pick the term, and optionally add annual property tax and homeowner's insurance so the payment reflects what you'd really send each month. The result updates with a payment figure, the total interest over the life of the loan, and a year-by-year amortization schedule you can expand.
How the mortgage payment is calculated
The monthly payment uses the standard amortization formula: M = P × r ÷ (1 − (1+r)−n), where P is the loan amount (price minus down payment), r is the monthly interest rate (APR ÷ 12), and n is the number of monthly payments (years × 12). Property tax and insurance are divided by 12 and added on top — lenders call the combined figure PITI (principal, interest, taxes, insurance).
A worked example
Take a $350,000 home with $70,000 down (20%) at 6.5% for 30 years. The loan is $280,000, the monthly principal-and-interest payment is $1,770, and over 360 payments you'd pay roughly $357,000 in interest — more than the original loan. Drop the term to 15 years and the payment rises to about $2,439, but total interest falls to roughly $159,000. That trade — about $670 more per month for $198,000 less interest — is the single most consequential choice on the form.
What the amortization schedule tells you
Early payments are mostly interest; later payments are mostly principal. On a 30-year loan at 6.5%, roughly two-thirds of your first year's payments go to interest, and you don't cross the 50/50 point until around year 19. That's why extra principal payments early in the loan save dramatically more than the same payments made later — and why the schedule matters more than the monthly number.
Rules of thumb before you borrow
Lenders approve up to 43–50% debt-to-income, but a payment at or below 28% of gross income leaves room for maintenance, savings, and life. A 20% down payment avoids PMI (typically 0.5–1.5% of the loan per year — $117–$350/month on a $280,000 loan). Compare any rate quote against the weekly Freddie Mac national average: more than 0.5% above it means get two more quotes, because on this example each 0.5% of rate is worth roughly $90/month. Finally, budget 1–2% of the home's value per year for maintenance — the payment is the floor of what ownership costs, not the ceiling.