Missing Loan Variable Calculator
Missing Loan Variable Calculator
Know three of four? Solve for payment, rate, term, or amount.
Know three of four? Solve for payment, rate, term, or amount.
Generated from the inputs below — a record you can revisit, or share with anyone helping you plan.
To repay $20,000 at 8% over 60 months.
Share of everything you pay that goes to interest rather than principal.
| Year | Interest | Principal | Balance |
|---|---|---|---|
| 1 | $113 | $293 | $16611 |
| 2 | $88 | $317 | $12941 |
| 3 | $62 | $343 | $8966 |
| 4 | $34 | $372 | $4662 |
| 5 | $3 | $403 | $0 |
| Period | Interest | Principal | Balance |
|---|---|---|---|
| 1 | $133 | $272 | $19728 |
| 5 | $126 | $280 | $18621 |
| 9 | $118 | $287 | $17484 |
| 13 | $111 | $295 | $16316 |
| 17 | $103 | $303 | $15117 |
| 21 | $95 | $311 | $13886 |
| 25 | $86 | $319 | $12622 |
| 29 | $78 | $328 | $11323 |
| 33 | $69 | $337 | $9990 |
| 37 | $60 | $346 | $8621 |
| 41 | $50 | $355 | $7214 |
| 45 | $41 | $365 | $5770 |
| 49 | $31 | $374 | $4287 |
| 53 | $21 | $385 | $2764 |
| 60 | $3 | $403 | $0 |
Free financial calculators, verified against primary sources like the IRS, CFPB and Federal Reserve. No sign-up, and every calculation runs entirely in your browser — nothing you type is ever sent to us.
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Open calculatorA fixed-rate loan is fully described by four values: the principal borrowed, the interest rate, the term, and the payment. They are locked together by a single equation, which means any three determine the fourth exactly. There is nothing to estimate.
Solving for payment or principal is straightforward algebra. Solving for the term requires logarithms:
Solving for the rate is the interesting case: the equation cannot be rearranged to isolate r. No closed-form solution exists. Calculators find it numerically instead, converging on the rate that reproduces the known payment — this tool uses bisection to about twelve decimal places.
Four situations account for nearly all real use of this calculation.
One check worth internalising: if your payment does not exceed the first month's interest, the balance grows rather than shrinks and no valid term exists. This calculator flags that case explicitly instead of returning a nonsense number.