A mortgage calculator estimates the fixed monthly principal and interest payment from the loan amount, APR, and term. Use it to compare 15- vs 30-year terms before talking to a lender. Escrow, property taxes, and insurance are not included here.
The Formula Behind the Mortgage Calculator
Monthly rate r = APR ÷ 12 ÷ 100.
Payment = P × r(1+r)^n ÷ ((1+r)^n − 1), where n is months in the term.
Worked Example
A $300,000 loan at 6.5% APR for 30 years (360 months):
- Monthly rate: r = 6.5 ÷ 12 ÷ 100 = 0.0054167
- Payment = 300,000 × 0.0054167 × (1.0054167)^360 ÷ ((1.0054167)^360 − 1)
- Monthly principal & interest = $1,896.20
- Total paid over 30 years = $682,633.47, of which $382,633.47 is interest
For comparison, the same loan over 15 years (180 months) costs $2,613.32 per month but only $170,397.98 in total interest — more than $212,000 less. Try both terms in the calculator above to see the trade-off for your own numbers.
When This Calculator Helps
Ballpark P&I before talking to a lender. For EMI-style tenure in months, use the EMI Calculator.
Using the Calculator
- Enter the values labeled in the tool above.
- Read the result cards — they update as you type.
- Cross-check one example by hand using the formula in this section.
- Open a related calculator below if your question needs a different formula.
Mistakes to Avoid
- Forgetting property tax and insurance in real budgets
- Comparing APR to a teaser rate unfairly
- Treating the result as a binding loan offer
Getting the Most Out of It
- Try 15 vs 30 years to see interest change
- Payoff timelines: Loan Payoff Calculator
More Calculators to Try
Limits of this estimate
Results are estimates for learning and planning — educational arithmetic only, not professional financial, tax, or payroll advice. They are not loan offers, and you should review our disclaimer before relying on any figure for a contract or filing.
Rounding may differ slightly from bank or spreadsheet software, and the figures do not include fees, taxes, insurance, or employer rules unless noted.