These results are estimates produced by the formulas below. They are provided for general information and are not professional financial or medical advice.
- M
- monthly principal-and-interest payment, in dollars per month
- P
- loan amount = principal (home price) − down payment, in dollars
- r
- monthly interest rate as a decimal = annual rate ÷ 12 ÷ 100
- n
- total number of monthly payments = loan term in years × 12
- interestRate
- annual mortgage interest rate, in percent per year
- downPayment
- upfront cash paid toward the home price, in dollars
- propertyTax
- annual property tax, in dollars per year
- homeownersInsurance
- annual homeowners insurance premium, in dollars per year
- pmi
- annual private mortgage insurance rate, in percent of the loan amount per year
Basic: a $300,000 loan amount with 0% down, a 3.5% annual interest rate, and a 30-year term gives r = 3.5 ÷ 100 ÷ 12 = 0.0029167 and n = 30 × 12 = 360. Then M = 300,000 × [0.0029167 × 1.0029167^360] ÷ [1.0029167^360 − 1] ≈ $1,347.13 per month in principal and interest.
Advanced: a $300,000 home price with $60,000 down (20%), a 4.5% annual rate, 30 years, $3,600 annual property tax, and $1,200 annual insurance gives $1,216.04 principal and interest + $300 tax + $100 insurance + $0 PMI (because the down payment is 20%) ≈ $1,616.04 per month. With $30,000 down (10%) the PMI rate of 0.5% adds 0.5% × $270,000 ÷ 12 = $112.50, for a total of ≈ $1,880.55 per month.
Formulas last reviewed against the sources above on 2026-10-08. No credentialed professional reviewer was involved.