How it works
The fixed monthly payment uses the standard amortizing-loan formula:
M = P × [ r(1 + r)n ] / [ (1 + r)n − 1 ]
- P = loan amount · r = monthly rate (annual ÷ 12) · n = number of payments
Each month, interest = balance × r; the rest of the payment reduces the principal. Early on most of the payment is interest; later, most is principal.
Worked example
$250,000 over 30 years at 6.5%:
- Monthly payment ≈ $1,580
- Total interest over 30 years ≈ $318,900