Loan amortization guide
Use this amortization calculator to see exactly how a fixed loan payment is divided between principal and interest, how the balance changes over time, and how extra principal can shorten the payoff schedule.
Need to estimate taxes, homeowners insurance, PMI, and total housing costs? Use our Mortgage Calculator. This calculator focuses on the loan payment and amortization schedule itself.
Calculation Methodology & Assumptions
The calculator uses one fixed-rate monthly amortization engine for the snapshot, chart, annual summary, monthly schedule, extra-payment comparison, and practical example.
- Loan principal
- The principal is the amount initially borrowed. It is the starting balance from which interest and repayment are calculated.
- Interest rate
- The entered annual interest rate is divided by 12 to obtain the monthly periodic rate used for the schedule.
- Monthly payment formula
- For a positive rate, M = P * [r(1+r)^n] / [(1+r)^n - 1], where M is the payment, P is principal, r is the monthly rate, and n is the number of payments. In plain English, the formula spreads repayment and interest over the selected term while keeping the scheduled payment level. At 0%, payment equals principal divided by the number of payments.
- Principal
- The principal portion of a payment reduces the outstanding loan balance. Extra payments are applied directly to principal in this estimate.
- Interest
- Interest is the borrowing cost for the period, calculated from the balance at the start of that payment period.
- Remaining balance
- The remaining balance is the unpaid principal after the scheduled and optional extra principal for that payment.
- Extra payments
- Extra principal does not recast the required payment. It reduces the balance, which can reduce future interest and shorten the term.
- Rounding and lender differences
- Actual schedules can differ because lenders may round each period, use exact payment dates or daily interest, include fees, or follow contract-specific rules.
Amortization Example
For a $250,000 loan at 6.5% over 30 years, the values below are generated by the same calculation engine used by this page.
| Monthly payment | — |
|---|---|
| Total interest | — |
| Total paid | — |
| First payment principal / interest | — |
Early payments often contain more interest because the starting balance is largest. As principal is repaid, the interest charge generally falls and a larger share of the scheduled payment reduces the balance.
Understanding amortization
What is amortization?
Amortization is the process of repaying a loan through regular payments that cover interest and reduce principal.
How does an amortization schedule work?
Each row applies the period interest to the starting balance, then applies the rest of the scheduled payment to principal and shows the new balance.
Why is there more interest at the beginning?
Interest is calculated on the outstanding balance. A larger balance at the start produces a larger interest amount, even when the scheduled payment is level.
What is principal?
Principal is the amount borrowed and the portion of a payment that lowers what remains owed.
What is interest?
Interest is the periodic cost charged for using the borrowed money. This estimate calculates it from the beginning balance of each month.
How does the remaining balance change?
The balance falls by the scheduled principal and any extra principal. The decline usually accelerates as the interest portion becomes smaller.
How do extra payments affect amortization?
An extra principal payment lowers the balance immediately in this model, reducing later interest and potentially shortening the payoff timeline.
Can I pay off an amortized loan early?
Many loans allow additional principal, but contract rules and prepayment terms vary. Confirm how your lender applies overpayments before relying on the estimate.
Why might my lender schedule differ?
Differences can come from rounding, payment dates, daily-interest conventions, fees, escrow, rate changes, or other loan-specific terms.
Frequently asked questions
What is an amortization schedule?
It is a payment-by-payment record showing scheduled payment, principal, interest, and the remaining balance.
How is a monthly amortized loan payment calculated?
A fixed-rate formula uses the principal, monthly interest rate, and number of payments to produce a level scheduled payment. A 0% loan uses principal divided by payments.
Why do early loan payments contain more interest?
The balance is highest at the beginning, so the interest charge is highest. Later payments usually allocate more to principal.
How much interest will I pay over the life of my loan?
The estimate is the sum of the interest rows in the schedule. Compare it across terms and extra-payment scenarios rather than looking only at the monthly payment.
How do extra payments change an amortization schedule?
Extra principal lowers the balance and future interest while the required scheduled payment stays the same, unless your lender recasts the loan.
Can extra payments reduce my loan term?
Yes, an extra-principal scenario generally reaches a zero balance sooner, subject to the lender applying the payment as requested.
What happens with a 0% interest loan?
The calculator divides the principal equally across the scheduled payments and shows zero total interest without using a division-by-zero formula.
Why does my lender's amortization schedule differ from this calculator?
Lender schedules may use different rounding, payment dates, daily-interest methods, fees, or contract terms. Use the lender disclosure for the official figures.
Trust and methodology
Sources: Consumer Financial Protection Bureau amortization guidance and CFPB Loan Estimate resources. Results are educational estimates and not financial, lending, tax, or legal advice.