Amortization Calculator

An amortization calculator breaks down every payment you will make on a loan into two components: the portion that reduces your principal balance and the portion that covers interest.

Reviewed by: CalcMojo Editorial Team

Whether you are evaluating a 30-year mortgage, a 5-year auto loan, or a personal loan with a fixed rate, this tool generates a complete month-by-month schedule so you can see exactly where your money goes.

Use the extra payments feature to model one-time lump sums or recurring additional principal payments. The calculator instantly recalculates your payoff date, total interest paid, and remaining balance so you can compare scenarios side by side. When you find a schedule you like, export the full table to CSV for your records, share it with your financial advisor, or print it directly from the page.

Understanding amortization is one of the most practical financial skills you can develop. Most borrowers do not realize that during the early years of a mortgage, the majority of each payment goes toward interest rather than principal. This calculator makes that reality visible, payment by payment. You can also toggle between monthly and biweekly payment frequencies to see how splitting your payment in half and paying every two weeks can shave years off your loan and save thousands in interest.

What Is Amortization?

Amortization is the process of spreading a loan into a series of fixed payments over a set period. Each payment covers two things: a portion of the outstanding principal and the interest charged on the remaining balance. In the early months of a loan, interest takes up the larger share of each payment because the outstanding balance is still high. As you continue making payments and the balance shrinks, the interest portion decreases and the principal portion grows. By the final payment, nearly the entire amount goes toward retiring the remaining balance.

The engine behind every amortization schedule is the standard amortization formula, commonly referred to as the PMT formula:

M = P[r(1+r)^n] / [(1+r)^n – 1]

In this formula, M is the monthly payment, P is the principal loan amount, r is the monthly interest rate (annual rate divided by 12), and n is the total number of payments. This formula ensures that each payment is identical in size while the internal split between principal and interest shifts over the life of the loan.

For example, on a $300,000 mortgage at 6.5% annual interest over 30 years, the monthly payment comes to approximately $1,896. In the first month, about $1,625 of that payment covers interest and only $271 reduces the principal. Fast-forward to month 180 (the halfway point), and the split is closer to $1,100 in interest and $796 in principal. The total amount of interest paid over the full 30-year term exceeds $382,000, meaning you pay more in interest than the original loan amount. That reality alone makes it worth exploring strategies to accelerate payoff.

How Extra Payments Save You Money

One of the most powerful features of this amortization calculator is the ability to model extra payments. Even modest additional principal payments can produce dramatic savings over the life of a loan because they reduce the balance that accrues interest in every subsequent month.

Consider the same $300,000 mortgage at 6.5% over 30 years. If you add just $200 per month in extra principal payments starting from the first month, the results are striking. Your loan payoff date moves from 30 years to approximately 22 years and 7 months, cutting roughly 7 years and 5 months off the term. The total interest paid drops from about $382,600 to approximately $262,400, a savings of over $120,000. That $200 monthly extra payment, totaling roughly $54,200 over the shortened term, generates more than twice its cost in interest savings.

Larger extra payments amplify the effect. Adding $500 per month to the same loan shortens the term to about 18 years and saves over $190,000 in interest. A single lump-sum payment of $10,000 applied in year one saves approximately $27,000 in interest over the remaining life of the loan.

The key insight is that extra payments made early in the loan have the greatest impact. A $5,000 extra payment in year one saves significantly more interest than the same $5,000 payment made in year 15, because the early payment reduces the principal on which interest compounds for many more years. Use the calculator to experiment with different extra payment amounts and timing to find a strategy that fits your budget.

Reading an Amortization Schedule

An amortization schedule is a table that lists every payment from the first month to the last. Understanding its columns helps you make informed decisions about your loan.

Payment Number — This column simply counts each payment in sequence. For a 30-year monthly mortgage, you will see payments numbered 1 through 360.

Payment Amount — The fixed monthly amount you owe. This stays the same throughout the loan unless you have an adjustable-rate mortgage or make extra payments that alter the schedule.

Principal Portion — The part of each payment that reduces your outstanding loan balance. This amount starts small and grows over time. Watching this column increase is a good indicator of your equity building.

Interest Portion — The part of each payment that goes to the lender as the cost of borrowing. This starts large and decreases over time. In the early years of a 30-year mortgage, interest can consume 80% or more of each payment.

Extra Payment — If you model additional payments using the calculator, this column shows the extra amount applied to principal in each period.

Remaining Balance — The outstanding principal after each payment is applied. This column starts at your original loan amount and counts down to zero. It is the most direct measure of how much you still owe.

When reviewing a schedule, pay attention to the crossover point where the principal portion of each payment first exceeds the interest portion. For a standard 30-year mortgage at current rates, this crossover typically does not occur until somewhere between year 15 and year 20, depending on the interest rate. Knowing this can motivate you to make extra payments that accelerate the crossover.

Biweekly vs Monthly Payments

Switching from monthly to biweekly payments is one of the simplest ways to pay off a loan faster without dramatically changing your budget. With a biweekly schedule, you make half of your monthly payment every two weeks. Because there are 52 weeks in a year, this results in 26 half-payments, which equals 13 full monthly payments instead of 12. That one extra payment per year goes entirely toward principal.

On a $300,000 mortgage at 6.5%, switching to biweekly payments (paying $948 every two weeks instead of $1,896 once a month) shortens the loan term by about 4 to 5 years and saves roughly $65,000 to $75,000 in total interest. The monthly cash flow impact is minimal because you are simply redistributing the same payment more frequently, with only one extra payment’s worth of cash spread across the year.

Before switching to a biweekly schedule, check with your lender. Some lenders offer formal biweekly programs, while others require you to make the equivalent adjustment yourself by adding one-twelfth of your monthly payment to each month’s check. Also confirm that your lender applies biweekly payments immediately rather than holding them until the end of the month, as the timing of application affects the interest savings.

Use the Mortgage Calculator to compare your current monthly payment against a biweekly structure, or the Loan Calculator if you are evaluating a non-mortgage loan.

When to Refinance Based on Your Amortization Schedule

Your amortization schedule is a valuable tool for deciding whether refinancing makes financial sense. Refinancing replaces your existing loan with a new one, typically at a lower interest rate or different term, and it resets the amortization clock. That reset is the critical detail many borrowers overlook.

If you are 10 years into a 30-year mortgage, you have already paid through the most interest-heavy portion of the schedule. Refinancing into a new 30-year loan at a lower rate might reduce your monthly payment, but it restarts the amortization process, meaning you will again be paying mostly interest in the early years of the new loan. The net interest savings may be smaller than they appear.

A more strategic approach is to refinance into a shorter term. If rates have dropped and you can afford the higher payment, refinancing from a 30-year to a 15-year mortgage significantly reduces total interest. Use this amortization calculator to model both scenarios: the remaining payments on your current loan versus the full schedule of a refinanced loan. Compare the total interest paid in each case, and factor in closing costs to determine the true break-even point.

As a general rule, refinancing tends to be worthwhile when you can reduce your rate by at least 0.75 to 1 percentage point, you plan to stay in the home long enough to recoup closing costs, and you do not extend your loan term significantly. The Compound Interest Calculator can help you evaluate what you might earn by investing the monthly savings instead of applying them to the mortgage, giving you a fuller picture of the opportunity cost.

This calculator provides estimates for informational purposes only. It is not financial advice. Results may not reflect your actual loan terms, tax situation, or investment returns. Consult a licensed financial advisor, CPA, or mortgage professional before making financial decisions.

Sources & Methodology

Amortization schedules generated using the standard amortization formula (PMT): M = P[r(1+r)^n]/[(1+r)^n-1]. Extra payments reduce principal directly, recalculating interest each month on the reduced balance.

Default rates shown are illustrative. Always verify current rates with your lender. Data accurate as of: March 2026