How an Amortization Schedule Works
An amortization schedule is the month-by-month map of a loan: every payment, how much is interest, how much is principal, and what you still owe. The math is deterministic — once you know the rate and term, the whole schedule is fixed.
What "amortization" means
A loan is amortized when each payment is the same size and gradually shifts from covering interest toward paying down principal. Early payments barely touch the balance; later payments almost entirely retire it. This "front-loaded interest" shape is the single most misunderstood part of borrowing.
The formula
Each month, interest is charged on the remaining balance, and whatever is left of your fixed payment reduces the principal:
interestmonth = balance × (annualRate ÷ 12)
principalmonth = payment − interestmonth
new balance = balance − principalmonth
Because the balance shrinks every month, the interest charge shrinks too — so a constant payment covers a growing slice of principal. That is the entire mechanism.
Worked example: $300,000 at 6.5% over 30 years
The fixed monthly payment is $1,896. Total interest over the life of the loan is $382,560. Watch how the split changes:
| Point in loan | Interest part | Principal part | Balance left |
|---|---|---|---|
| Payment 1 | $1,625 | $271 | $299,729 |
| Payment 180 (year 15) | $1,178 | $718 | $217,521 |
| Final payments | ~$10 | ~$1,886 | $0 |
By the midpoint you are paying more principal than interest — but only because the balance has finally fallen far enough. For the first ~13 years, the majority of every payment is interest.
Why this matters for paying off early
Extra payments do the most good early, when the balance (and therefore the interest rate applied to it) is highest. A $200 extra payment in year 2 removes far more future interest than the same $200 in year 25, when the balance is already small. This is why "pay a little extra from the start" is the highest-leverage habit on any amortizing loan.
Frequently asked questions
Does my lender's statement match this exactly?
It matches standard fixed-rate amortization. Small rounding differences from your lender are normal. For taxes or legal purposes, rely on the official statement.
What about variable-rate loans?
The schedule reshapes whenever the rate changes — the same mechanics apply, but the payment or term adjusts. Run a fixed-rate snapshot to see the current split.
How do I see my own schedule?
Use the Amortization calculator to generate the full month-by-month table for your exact numbers, or the Loan Balance calculator to see where you stand after payments already made.
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