Amortization Calculator

How to use the loan amortization calculator

What this calculator does

This calculator estimates the regular monthly principal-and-interest payment for a fully amortizing, fixed-rate loan and builds the payment schedule that reduces the balance to zero. It also models optional recurring and one-time extra principal payments, then reports the resulting payoff date, interest savings, and months saved. It is useful for mortgages, auto loans, personal loans, and other installment debt that follows a fixed monthly rate and payment pattern. It does not include taxes, insurance, origination charges, late fees, changing rates, daily-interest conventions, escrow, or lender-specific payment-allocation rules. The Consumer Financial Protection Bureau explains that a typical fixed-rate payment keeps the combined principal-and-interest amount steady while the split changes over time in its guide to how mortgage principal and interest are paid down.

When to use it

Use the calculator to compare a shorter versus longer loan term, estimate the cost of a quoted interest rate, review how much of early payments goes to interest, or test whether extra principal could produce a meaningful payoff acceleration. It is also helpful when checking a lender’s proposed schedule or preparing a month-by-month repayment plan for budgeting.

How to calculate

1. Enter the Loan amount in U.S. dollars, then set the Loan term using whole Years and Months.
2. Enter the annual Interest rate as a percentage and choose the Loan start date. The selected month becomes payment period one.
3. To test prepayments, select Optional: make extra payments. Add an Extra monthly pay amount and start date, an Extra yearly pay amount and start date, or one or more Extra one-time pay entries. Use More one-time payments for additional dated lump sums.
4. Read the live results, cost breakdown, trend chart, and annual summary. Switch to Monthly schedule for every payment period.
5. Select Download Excel to export the current assumptions and complete schedule to a validated XLSX workbook. Select Reset to restore the original $200,000, 15-year, 6% assumptions and remove all extra-payment changes.

Input guide

Loan amount is required currency greater than zero; enter values such as $200,000.00. A larger balance increases the payment and total interest when other assumptions stay fixed. Use en-US grouping and a decimal point; ambiguous forms such as “1,5” are rejected. Loan term is required and combines whole years and months into 1–1,200 monthly periods. For example, 15 years and 0 months equals 180 payments. A longer term generally lowers the required payment but raises total interest. Interest rate is a required annual percentage from 0% to 100%; 6.00% is a valid example. A higher rate increases interest and the monthly payment. Loan start date requires a month and a four-digit year from 1900 to 2300; it controls schedule labels and the dates on which extras begin, not the payment formula itself.

Optional: make extra payments is a binary control. When enabled, Extra monthly pay accepts nonnegative dollars and applies every month beginning with its selected month and year. Extra yearly pay accepts nonnegative dollars and applies once each year in its selected month after the start date is reached. Extra one-time pay accepts a nonnegative amount and an exact month and year; multiple entries due in the same month are combined. Extra amounts reduce principal after the regular interest charge is calculated. Entering a date outside the displayed loan horizon simply produces no effect. Before relying on a prepayment scenario, confirm how your servicer applies extra funds; the CFPB notes that borrowers should verify that allowed extra payments are applied to principal in its summary of mortgage-servicing and extra-principal rules.

Output guide

Monthly Pay is the fixed scheduled principal-and-interest payment before optional extras. Total of monthly payments is the sum of actual scheduled and extra payments through payoff. Total interest is the borrowing cost produced by the schedule. Payoff date is the month of the final payment. Interest saved and Months saved compare the active extra-payment schedule with the same loan without extras; both are zero when extras have no effect. Principal share is the original principal divided by total payments, expressed as a percentage. These are estimates based on the entered fixed-rate assumptions, not lender quotes.

The Principal and interest breakdown chart compares two mutually exclusive parts of total payments: original principal and total interest. At a 0% rate, interest is zero, so the calculator replaces the two-part chart with a compact explanation rather than drawing a one-category ring. The Balance and principal over time chart uses annual points for Remaining balance and Cumulative principal. The monthly table columns are Payment, Date, Interest, Principal, and Ending Balance; the annual table aggregates the same interest and principal amounts by loan year.

Worked example

For a $200,000 loan over 15 years at 6% annually, the monthly rate is 0.06 ÷ 12 = 0.005 and the term is 180 months. The standard payment formula is payment = principal × rate ÷ (1 − (1 + rate)^−months). That produces $1,687.71 per month. In payment one, interest is $200,000 × 0.005 = $1,000.00; the remaining $687.71 reduces principal, leaving $199,312.29. Across the full schedule, total payments are $303,788.46 and total interest is $103,788.46, subject to cent-level display rounding.