Loan calculator help

By FinTools Content updated October 1, 2026

The loan calculator estimates fixed monthly principal and interest from a loan amount, annual interest rate and target number of months.

Input limits and formats

• Principal: $1 to $1 billion, in US dollars, with at most two decimal places.
• Annual interest rate: 0% to 100%, fixed for the entire loan. These are model bounds, not suggested rates.
• Target term: 1 to 600 whole months. Multiply years by 12; for example, 3 years is 36 months.

Every field is required. Use plain digits and a decimal point without commas, spaces, currency or percent symbols. Principal and months do not accept exponent notation. A very small interest rate can use exponent notation, such as 1e-8. Invalid or blank fields hide results and CSV export, and disable saving, copying and PNG download until corrected. A valid shared link can still restore the calculator.

Which rate should I enter?

Enter the loan's annual interest rate. APR may include fees in addition to interest, so entering a fee-inclusive APR does not recreate the lender's principal-and-interest schedule. The calculator does not retrieve current rates, assess eligibility or include taxes and insurance.

Why does the last payment differ?

Regular payments and monthly interest use whole cents. The last payment covers only remaining principal plus that month's interest. For $10,000 at 6% with a 36-month target, the regular payment is $304.22 and the final payment is $304.18. The sum of all principal reductions is exactly the entered loan amount.

Why is the actual payoff earlier?

The target is a maximum repayment term, not a promised exact maturity. This model chooses the smallest whole-cent payment that repays within it. For $1,000 at 0% over a target of 600 months, $1.67 repays in 599 months; one cent less would take too long. Very small loans and extreme rate/term combinations can finish much earlier. Both the target and actual payoff appear in the results and shared PNG.

How is interest rounded?

Each month uses round(balance cents × annual percent / 1200), then subtracts the principal portion of the payment. Tiny positive rates can legitimately round to zero cents of monthly interest. This uses standard JavaScript numbers; floating-point boundaries, daily interest, payment dates or lender rounding can produce different results. Read the full calculation method and examples.

Save, restore or compare a calculation

Download monthly schedule CSV exports every payment, opening and remaining balances, interest and principal in USD with exact cents. It includes your current input text, target and actual payoff months, regular and final payments, totals, source URL and model limitations. Open it in a spreadsheet to inspect the schedule; the export uses the same monthly rounding as the displayed results. Invalid inputs hide the download until corrected. A CSV contains your assumptions, so share it only as intended.

Save as new stores named inputs in this browser. Load opens the saved library; Update selected replaces only the loaded record. A scenario link restores inputs and recalculates results without saving them. A PNG contains the summary and assumptions, not the full monthly table. Clearing site data can remove saved records. See privacy and terms.

To compare several existing debts and extra payments, use the debt payoff calculator with actual lender minimums. Return to all calculator help or the calculator directory. These are educational estimates, not financial advice or guaranteed lender results.