What an amortization schedule tells you
An amortization schedule is the complete payment map of a loan. For every period it shows three numbers: how much of your payment covered interest, how much reduced your principal, and what balance remains. Reading it reveals the two facts most borrowers find surprising:
- Early payments barely dent the balance. On a 30-year, $250,000 loan at 7%, you pay about $20,000 in the first year — but the balance only drops by roughly $2,500.
- Total interest can rival the loan itself. That same loan costs about $349,000 in interest over 30 years — more than the amount borrowed.
The amortization formula
Fixed loan payments come from a single formula:
where M is the monthly payment, P the principal, r the monthly interest rate (annual ÷ 12), and n the number of payments. Each month, interest equals the current balance × r; whatever is left of your payment reduces principal. This calculator runs that loop month by month and rolls the results up by year.
How to use the schedule to save money
1. Compare loan terms honestly
Run the same amount and rate at 15 vs. 30 years. The 15-year payment is higher, but total interest usually falls by more than half. If the higher payment scares you, remember the hybrid strategy: take the 30-year for safety and pay it like a 15-year using the extra-payment field above.
2. See what a rate difference is really worth
A quarter-point sounds trivial. On $250,000 over 30 years, dropping from 7.00% to 6.75% saves about $15,000 in lifetime interest. That number tells you how many points are worth buying, and whether refinancing fees would pay for themselves.
3. Watch the crossover point
Scan the schedule for the year when principal paid overtakes interest paid. At 7% on a 30-year loan that happens around year 20 with no extra payments — and years earlier with even a modest extra payment. If you're deciding whether to prepay your mortgage, that crossover shows why early extra dollars matter most.
Which loans amortize this way?
Fixed-rate mortgages, auto loans, personal loans, and most student loans all follow this schedule. Credit cards do not — they have no fixed term, and minimum payments are recalculated monthly (see our credit card payoff calculator for that math). Adjustable-rate mortgages amortize too, but the schedule resets each time the rate adjusts.