How an Amortization Schedule Works

The core idea: the payment is fixed, the split is not

On a standard fixed-rate installment loan, the monthly payment amount never changes for the entire term. What changes every single month is how that fixed payment is divided between two parts:

• Interest: calculated fresh each month as your current outstanding balance multiplied by the monthly interest rate.
• Principal: whatever is left of the payment after interest is covered, which directly reduces your balance.

Because interest is always calculated on the CURRENT balance, and that balance keeps shrinking every month as you pay down principal, the interest portion of your payment shrinks a little every month too, and the principal portion grows to make up the difference. That is the entire mechanism behind amortization, described in three sentences.

A full worked example, year by year

Take the same $10,000 loan at 5% annual interest for 3 years (36 months) used in the loan payment formula walkthrough, which works out to a fixed payment of $299.71/month. Here is the complete yearly amortization schedule for that loan:

A few things worth noticing in this table. First, the starting balance of each row exactly matches the ending balance of the row before it, a useful check when you're building or verifying a schedule by hand. Second, the interest column drops sharply each year (from $428.04 in year 1 down to just $95.54 in year 3) even though the total amount paid stays the same, roughly $3,596.52 per year ($299.71 × 12). Third, the very last year's ending balance lands on exactly $0.00: that is the entire point of an amortizing loan, the fixed payment is calculated specifically so the balance reaches zero on schedule, not a cent early or late.

Why the first year always carries more interest

Compare year 1's interest ($428.04) to year 3's interest ($95.54) in the table above, a more than 4x difference on the exact same loan. This is not a coincidence or a quirk of this particular example: it is a mathematical certainty of any amortizing loan. Interest is charged on whatever balance remains, and the balance is always at its highest at the very start of the loan. As principal gets paid down, there's simply less balance left to charge interest on, so later payments are able to put a larger share toward principal instead. This is also why paying extra toward principal early in a loan (when that option is available and not restricted by a prepayment penalty) has an outsized effect on the total interest paid over the life of the loan, compared to the same extra amount paid later in the term.

Monthly vs. yearly schedules

A full amortization schedule can be shown month by month (36 individual rows for a 3-year loan, 360 rows for a 30-year mortgage) or summarized year by year, as in the table above. The loan calculator generates a full monthly simulation internally to make sure every number is exact, then presents it grouped by year in the on-screen schedule so it stays readable rather than turning into a scroll of hundreds of nearly-identical rows. When you print or save the calculator's result as a PDF, the same yearly schedule is included on the printed page.

What an amortization schedule can tell you

Beyond satisfying curiosity about where your money goes, a schedule is genuinely useful for a few practical questions: how much of a specific future payment will go toward principal (useful for tax purposes on certain loan types, or for understanding how quickly you're building equity on a secured loan); what your remaining balance will be at any given point if you're considering refinancing or selling an asset the loan is attached to; and how much total interest you'll pay if you keep the loan for its full term versus paying it off early. Enter your own loan amount, rate and term into the calculator to generate a schedule for your specific numbers, entirely in your own browser (see the privacy policy for what is, and is not, collected).