How your monthly payment is calculated
This uses the standard amortization formula: M = P·r / (1 − (1+r)⁻ⁿ), where P is the amount, r the monthly rate, and n the number of months. Works for mortgages, car loans and personal loans with fixed rates.
The number banks don't headline
Look at total interest. On a 30-year mortgage at typical rates, interest can approach the size of the loan itself. Shortening the term or making extra principal payments early cuts that number dramatically — the bar above shows the split at a glance.