Repayment Calculator
Find how long it takes to repay a debt at a fixed monthly payment, and see total interest paid over the life of the loan.
How to use the Repayment Calculator
- Enter your inputs into the Repayment Calculator above.
- Results update instantly as you type — no submit button needed.
- Adjust any value to see how the result changes in real time.
The repayment time formula
n = −log(1 − P·r/M) / log(1 + r)
P is the balance, r is the monthly periodic rate, M is the fixed monthly payment. The result n is the number of months until the debt is fully paid.
Worked example
$10,000 debt at 8% APR with $250/month payment: n ≈ 47 months (just under 4 years). Total paid: $11,750. Interest: $1,750. Doubling the payment to $500/month finishes in about 22 months with only $830 in interest.
Frequently asked questions
What if my payment is below interest accrual?
If your monthly payment is less than one month of interest on the current balance, the balance grows instead of shrinking and you never pay it off — the formula will return an error or infinity.
Does this work for any type of debt?
Yes, as long as the rate is fixed and the payment is constant. Variable-rate debt (credit cards with minimum payments based on balance) needs a different calculation.
How much extra payment makes a real difference?
Even 10–20% extra per month typically cuts the payoff time by 25–40%, because extra payments come off the principal directly and avoid all future compounding.