Amortization Calculator
Loan Amortization Calculator
Model a fixed-rate loan, see every principal and interest payment, test optional extra payments, and export the current schedule to a genuine Excel workbook.
Loan assumptions
Optional extra payments
Recurring monthly
Recurring yearly
One-time payments
Live results
Payment breakdown
Principal repaid and interest paid across the modeled schedule.
| Category | Amount | Percent |
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Loan progress over time
Remaining balance compared with cumulative principal and cumulative interest.
| Series | Final value |
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Amortization schedule
Switch between a compact annual roll-up and the full monthly payment detail.
How to use this amortization calculator
This calculator estimates the payment pattern for a fully amortizing, fixed-rate loan. It calculates the regular monthly payment, separates each payment into interest and principal, projects the remaining balance, and shows how optional extra payments can shorten the schedule. The model is useful for mortgages, auto loans, personal loans, and other installment debt with a constant rate and regular monthly payments. It does not model variable rates, lender fees, taxes, insurance, payment holidays, or prepayment penalties.
Enter the core loan assumptions
Loan amount is the principal owed at the beginning of the schedule. Enter the amount actually financed, not the asset price unless those figures are the same. A higher principal raises the monthly payment and total interest. Zero produces a neutral result; negative amounts are rejected.
Loan term combines years and additional months. A longer term normally lowers the required monthly payment but increases lifetime interest because the balance remains outstanding longer. A shorter term does the opposite. The calculator requires at least one month and supports mixed terms such as 7 years and 6 months.
Annual interest rate is the nominal fixed rate used to calculate monthly interest. Enter 6 for 6%, not 0.06. A zero-rate loan is supported and divides principal evenly across the term. The rate here is not automatically the same as APR, because APR may include certain fees. The Consumer Financial Protection Bureau explains the distinction between interest rate and APR.
Loan start date anchors the schedule and determines when recurring or one-time extra payments begin. The first row represents the first monthly payment period starting from that month. Use the contractual schedule date when comparing results with lender documents.
Model optional extra payments
Extra monthly amount adds the same principal payment every month from the chosen start date. Even a modest recurring amount can reduce future interest because each subsequent interest charge is calculated on a smaller balance. Extra yearly amount applies once per year in the selected month, which can model an annual bonus or planned lump sum. One-time payments let you add multiple dated principal reductions. Add a row for each payment and remove rows that no longer apply.
Extra payments are capped at the remaining principal, so the final payment never drives the balance below zero. Before relying on an accelerated payoff strategy, verify whether the loan contract has a prepayment penalty and whether the servicer requires special instructions for principal-only payments. The CFPB provides guidance on making additional mortgage payments.
Interpret the results
Regular monthly payment is the contractual principal-and-interest payment calculated from the original amount, fixed rate, and original term. It excludes optional extras. Total payments includes scheduled payments plus every modeled extra payment. Total interest is the sum of monthly interest charges. The interest share shows how much of all modeled payments represents borrowing cost rather than principal repayment.
Projected payoff is the month of the last modeled payment. Months saved compares the accelerated schedule with the same loan without extras. Interest saved is the difference between baseline interest and interest after extras. A zero value means the optional payments do not change the schedule, generally because they are zero, fall after payoff, or lack a valid start date.
Read the charts and schedule
The payment-breakdown donut uses principal and total interest from the current model. Its percentages always reconcile to total payments. The progress chart shows three series: remaining balance, cumulative principal, and cumulative interest. A rapidly falling balance indicates faster equity buildup. The point where cumulative principal rises more quickly reflects the normal shift from interest-heavy early payments to principal-heavy later payments.
The annual schedule aggregates monthly rows by calendar year, while the monthly schedule shows each payment date, scheduled payment, extra principal, interest, principal, and ending balance. The ending balance should reach zero on the final row. Use the Excel export when you need the current assumptions, breakdown, and every schedule row in a workbook for further analysis.
Formula and practical limitations
For a positive monthly rate, the payment uses the standard annuity formula: principal multiplied by the monthly rate, divided by one minus the discount factor across all payments. Each month then calculates interest as the opening balance multiplied by the monthly rate. Principal is the scheduled payment minus interest, followed by eligible extra principal. For a zero rate, the payment is principal divided by the number of months.
Small differences from a lender statement can arise from day-count conventions, payment timing, rounding policy, escrow items, fees, or a rate that changes over time. The Federal Reserve’s consumer resources offer broader context on credit and borrowing decisions. Treat this output as an educational estimate rather than personalized financial, legal, tax, or investment advice.