How to Calculate Your Monthly Mortgage Payment (With Formula)
The formula looks intimidating but the concept is simple. Here is how lenders determine your monthly payment.
The mortgage payment formula: M = P × [r(1+r)^n] / [(1+r)^n - 1]. Where P = loan principal (amount borrowed), r = monthly interest rate (annual rate ÷ 12), n = total number of payments (years × 12). A $300,000 loan at 6.5% for 30 years: r = 0.065/12 = 0.00542. n = 360. M = $300,000 × [0.00542 × 1.00542^360] / [1.00542^360 - 1] = $1,896.
But That Is Not Your Total Payment
The $1,896 is principal and interest only. Your actual monthly payment also includes: property tax ($250-500/month depending on location), homeowner insurance ($100-250/month), and PMI if less than 20% down ($100-250/month). Total actual payment: $2,350-2,900. Always calculate the full PITI (Principal, Interest, Taxes, Insurance) payment, not just the mortgage amount.
How Much Each 0.5% Costs You
On a $300,000 30-year mortgage: 6.0% = $1,799/month, $347,515 total interest. 6.5% = $1,896/month, $382,633 total interest. 7.0% = $1,996/month, $418,527 total interest. Each 0.5% increase costs $100/month and $35,000-36,000 over the loan. This is why shopping multiple lenders and improving your credit score before applying is worth thousands.