Amortization Calculator

How Amortization Actually Works

Amortization is the process of spreading a loan into a series of equal payments over time so that the balance reaches zero by the end of the term. Each payment does two jobs at once: it covers the interest charged for that period, and it uses whatever is left to reduce the principal you owe. Because the payment amount is fixed but the balance keeps falling, the split between interest and principal shifts steadily over the life of the loan. This calculator builds the full schedule and lets you see how optional extra payments accelerate payoff.

The fixed payment itself comes from the amortization formula M = P[r(1+r)^n] / [(1+r)^n − 1], where P is the loan amount, r is the periodic interest rate (annual rate ÷ 12 for monthly payments), and n is the total number of payments. For each period, the interest portion is the current balance times r, and the remainder of the payment (plus any extra) reduces the principal.

Example: $200,000 at 5% for 30 Years

Suppose you have a $200,000 loan at a hypothetical 5% annual rate over 30 years. The monthly rate is about 0.4167% and there are 360 payments, producing a monthly payment of roughly $1,074. In the first month, interest is about $833 (200,000 × 0.004167) and only about $241 goes to principal. Years later, when the balance has dropped substantially, the interest portion is far smaller and most of the payment reduces principal. Watching this shift in the table below is the clearest way to understand why early payments build equity so slowly.

The Power of Extra Payments

Making additional principal payments is one of the most effective ways to save money on a loan. Because an extra payment permanently lowers your balance, every future interest charge is calculated on a smaller number, so the savings compound over the remaining term. On a long mortgage, even a modest recurring extra payment can remove years from the schedule and cut total interest meaningfully. Use the extra payment slider to see the exact impact on your specific loan, including the new payoff date and the total interest saved.

To see why, return to the $200,000 example at a hypothetical 5% over 30 years. Adding an extra amount on top of the roughly $1,074 scheduled payment means every dollar of that extra goes straight to principal. Each time the balance drops, the next month's interest charge is computed on a smaller number, so a growing share of your regular payment also shifts toward principal. The two effects reinforce each other, which is how a steady extra payment can retire the loan years ahead of schedule and erase a large slice of the interest you would otherwise owe. The earlier in the loan you start, the more pronounced the savings, because the balance, and therefore the interest, is at its highest.

Reading the Amortization Table

The table below shows how each payment is allocated. Key things to look for as you scan it:

• Interest column: Largest at the start and shrinking every period as the balance falls.
• Principal column: Small at first and growing over time, even though the total payment stays constant.
• Extra column: Any additional amount you apply, which goes entirely to principal and pulls the payoff date forward.
• Balance column: The remaining amount owed after each payment, which reaches zero in the final period.

Strategies to Pay Less Interest

Because total interest depends on how long your balance stays outstanding, anything that shrinks the balance faster saves money. A few practical approaches:

• Round up your payment: Paying a slightly higher round number each month sends the difference to principal automatically.
• Make biweekly payments: Paying half your monthly amount every two weeks results in one extra full payment per year, shortening the term.
• Apply windfalls: Directing a tax refund or bonus to principal early in the loan, when the balance is highest, has the largest effect.
• Refinance to a lower rate: A lower rate reduces the interest portion of every future payment, though you should weigh any closing costs.

Whichever method you use, confirm with your lender that extra funds are applied to principal. If they are credited toward your next scheduled payment instead, you will not get the interest savings you expect.

Amortization vs. the Other Loan Tools

Use this amortization calculator whenever you want a payment-by-payment breakdown or want to test extra payments on any fixed-rate loan. If you are buying a home or a car and need purchase-specific inputs, the mortgage and auto loan calculators add factors like down payments, sales tax, and trade-ins. For a quick payment estimate on a general installment loan without the detailed schedule, the loan calculator is the faster option.