How to Read an Amortization Schedule, Month by Month

An amortization schedule is your loan's complete ledger: every payment from the first to the last, each split into the part that pays interest and the part that actually retires debt. Reading it explains why early extra payments feel so powerful — and why the lender's share of your check starts so high.

The level payment

A fixed-rate loan is engineered so the payment never changes: it is set so that payment minus each month's interest exactly eats the principal down to zero on schedule. The standard formula (the full derivation lives in how loan interest works) is:

M = P × r × (1 + r)^n / ((1 + r)^n − 1)

with P the principal, r the monthly rate (annual ÷ 12) and n the number of payments. On a $300,000 loan at 6% for 30 years — r = 0.005, n = 360 — that gives $1,798.65 per month. Over the term the schedule totals $647,514 of payments, of which $347,514.57 is interest.

One month's mechanics

Each month the lender charges interest on the current balance at the monthly rate, then applies the payment: interest first, the remainder to principal.

month 1:  interest  = 300,000 × 0.005 = $1,500.00
          principal = 1,798.65 − 1,500.00 = $298.65
          balance   = 299,701.35
month 2:  interest  = 299,701.35 × 0.005 = $1,498.51
          principal = $300.14,  balance = 299,401.20

The principal portion grows by a factor of (1 + r) every month — 0.5% here — because the interest it displaces keeps shrinking. By the final row the split has fully inverted: month 360 is $8.95 of interest and $1,789.70 of principal, closing the balance to zero.

Reading the crossover

Because the split shifts one row at a time, there is a definite month where principal finally overtakes interest. On this loan it is month 223 of 360 — about 62% of the way through the term — where the payment divides into $903.71 of principal and $894.94 of interest. On a 15-year loan the crossover arrives far sooner, which is the same arithmetic that makes short terms cheaper: you never spend decades paying mostly interest.

What an extra payment changes

An extra amount applied monthly goes entirely to principal, and every dollar removed stops accruing interest for the rest of the term. Add $100 a month to this loan and the schedule ends at month 313 instead of 360 — 47 payments early — with total interest of $294,168.16 instead of $347,514.57: a saving of $53,346.41. From a January 2026 start the payoff date moves from January 2056 to February 2052. The same acceleration logic across many debts is the territory of mortgage payoff strategies and snowball versus avalanche; the schedule's job is to show it row by row on one loan.

Reading the whole table at a glance

Three columns repay attention. Balance shows how slowly the principal moves at first — five years in, more than half your payments have gone to interest, yet the balance has barely begun its slide. Interest is the running cost of the loan, and its early steepness is why prepayment math favors the first years. Principal is the equity-building column on a mortgage, the one that tells you how much of the house you actually own as the months pass. Escrowed taxes and insurance never appear here; they live outside the amortization math entirely — see mortgage math explained for how PITI sits on top of this table.

Try it yourself

Generate your own table with the Amortization Schedule Generator — enter principal, rate and term, or your exact monthly payment, with an optional extra amount and start date. For totals-only math the Loan Calculator is faster; to compare payoff strategies side by side, use the Loan Payoff Calculator.