Mortgage Calculator
By Santaji GadepatilinUpdated October 27, 2026
Monthly payment (principal + interest) vs Interest rate (annual) (%) — other inputs held at your current values.
How to use this calculator
Enter the home price, down payment %, interest rate and term. You get the loan amount, monthly payment and total interest. Work backwards to find the price you can afford or the down payment needed.
The formula
M = P × i × (1 + i)n ÷ ((1 + i)n − 1)
Worked example
A 400,000 home with 20% down, 6.5% for 30 years:
- Loan = 400,000 × 0.8 = 320,000
- Monthly payment = 2,022.62
- Total interest over 30 years = 408,142
15 vs 20 vs 30 years
For 320,000 at 6.5%:
| Term | Monthly payment | Total interest |
|---|---|---|
| 15 years | 2,787.54 | 181,758 |
| 20 years | 2,385.83 | 252,600 |
| 30 years | 2,022.62 | 408,142 |
A 15-year loan costs about 765 more each month but saves over 226,000 in interest.
Ways to pay less
- Bigger down payment — reduces the loan and often the rate.
- Extra payments — even one extra payment a year can cut years off a 30-year loan.
- Shop for the rate — 0.5% less on 320,000 over 30 years saves about 37,500.
Frequently asked questions
How is a mortgage payment calculated?
With the standard amortization formula M = P × i × (1 + i)ⁿ ÷ ((1 + i)ⁿ − 1), where P is the loan amount, i the monthly rate and n the number of months.
Does this include property tax and insurance?
No. This is principal and interest only. Add property tax, home insurance and any mortgage insurance to get your full monthly cost.
How much house can I afford?
Press × on Home price, then type the monthly payment you can afford. Many lenders like total housing costs to stay under about 28–36% of gross income.