Amortization Schedule Calculator — Principal vs Interest With Extra Payments

An amortization schedule shows exactly how every payment on a fixed-rate loan splits between principal and interest, from the first payment to the last. This split is not constant — early payments are overwhelmingly interest, while later payments are overwhelmingly principal, even though the total payment amount stays the same every month. Understanding this front-loaded pattern explains why paying off a mortgage early in the first few years saves dramatically more interest than making the same extra payment later in the loan term.

How to use this Amortization Schedule

1. 1Enter your loan amount, annual interest rate, and term in years.
2. 2Toggle between a yearly summary view (totals for each year of the loan) or a monthly view (every individual payment).
3. 3Review the principal and interest columns to see how the split shifts over the life of the loan.
4. 4Use the copy button to export the full schedule for your own records or spreadsheet analysis.
5. 5Compare an early year to a late year side by side to see the principal/interest shift concretely, rather than just conceptually.

Amortization schedule formula explained

Each payment in an amortization schedule is calculated the same way: interest for that period is the remaining balance multiplied by the monthly interest rate, and the rest of the fixed payment goes to principal. Because the balance shrinks every month, the interest portion shrinks too — which means the principal portion grows, even though the total payment never changes. This is why the principal/interest split visibly shifts over the life of the loan despite a constant monthly payment.

Amortization example: $300,000 loan at 6.5% over 30 years

1. 01Monthly payment: $1,896.20 (constant for all 360 payments).
2. 02Year 1 totals: $22,754.45 paid — only $3,353.18 (15%) goes to principal, $19,401.27 (85%) is interest.
3. 03Year 15 totals: same $22,754.45 paid — now $8,309.94 (37%) goes to principal, $14,444.51 (63%) is interest.
4. 04Year 30 (final year) totals: same $22,754.45 paid — now $21,973.15 (97%) goes to principal, just $781.30 (3%) is interest.
5. 05Total interest paid over the full 30-year term: $382,633.47 — more than the original loan amount itself.

What determines how your payments split between principal and interest?

Tips and things to know

• ✓If you want to pay off a loan faster and save interest, extra payments made in the early years of the schedule have a dramatically larger impact than the same extra payment made later — front-load extra payments whenever possible.
• ✓Use the monthly view to find the exact point where principal and interest portions cross over (the month where principal finally exceeds interest in each payment) for your specific loan.
• ✓Compare amortization schedules at different loan terms (e.g. 15-year vs 30-year) side by side — the monthly payment is meaningfully higher on a shorter term, but total interest paid is often less than half.
• ✓A biweekly payment schedule (26 half-payments per year instead of 12 full payments) effectively adds one extra full payment annually, which can meaningfully shorten a mortgage when applied consistently.
• ✓Refinancing resets the amortization schedule — a refinance partway through a loan term restarts the front-loaded interest pattern on the new balance, which is worth factoring into a refinance decision alongside the new rate.

Amortization Schedule — bottom line

An amortization schedule reveals something counterintuitive that trips up most borrowers: in the early years of a loan, the vast majority of each payment goes to interest, not principal. On a 30-year mortgage at 7%, more than 83% of the first payment is interest. You build equity slowly at first and accelerate toward the end. This is why extra payments made early in a loan have an outsized impact — each extra dollar of principal paid in year one eliminates 29 years' worth of interest on that dollar. The most important use of an amortization schedule is not to understand your current payment — it is to model extra payment scenarios. Look at the "remaining balance" column at year 5, 10, and 15. Now find the impact of paying $100, $200, or $500 extra per month. The principal reduction compounds because eliminating a row of the schedule also eliminates all the interest that would have been charged on that remaining balance. Common mistake one: making extra payments without specifying they should go to principal reduction. Extra payments default to "next month's payment" at many servicers, not to principal paydown. You must explicitly designate them as principal-only payments. Common mistake two: paying extra on low-interest debt when higher-interest debt exists. Extra payments on a 3.5% mortgage while carrying 22% credit card debt costs you 18.5% in opportunity cost per dollar. Pay the highest-rate debt first. Once that's clear, use this schedule to identify the exact payoff date impact of any extra payment amount you can commit to monthly. The Mortgage Payoff Accelerator Calculator lets you model this directly — enter your current balance and payoff target date to find the required extra payment.

Official resources and further reading