What Is the Debt Snowball Payoff Time Calculator?
This calculator estimates how many months it will take to pay off a single debt (such as a credit card or loan) given its current balance, annual interest rate (APR), and a fixed monthly payment. It uses the standard amortization formula to account for interest accruing on the remaining balance each month.
How to Use It
Enter your current outstanding balance, the annual percentage rate (APR), and the fixed amount you plan to pay each month. The calculator returns the number of months to full payoff, the equivalent in years, the total amount you'll pay, and the total interest. If your payment is too low to cover the monthly interest, the calculator will warn you that the debt can never be paid off.
The Formula Explained
The number of payments is derived from the loan amortization equation:
$$N = \frac{-\ln\!\left(1 - \dfrac{B \cdot r}{P}\right)}{\ln(1 + r)}$$
where \(B\) is the balance, \(P\) is the monthly payment, and \(r = \dfrac{\text{APR}}{100 \times 12}\) is the monthly interest rate.
The term inside the logarithm must be positive, which requires that your payment exceeds the first month's interest charge (\(B \cdot r\)). Otherwise the balance never shrinks.
Worked Example
Suppose you owe $5,000 at 18% APR and pay $200 per month. The monthly rate is \(r = 0.18 / 12 = 0.015\). Then $$N = \frac{-\ln\!\left(1 - \dfrac{5000 \times 0.015}{200}\right)}{\ln(1.015)} = \frac{-\ln(1 - 0.375)}{\ln(1.015)} = \frac{-\ln(0.625)}{0.0148886} \approx \frac{0.47000}{0.0148886} \approx 31.57.$$ Rounding up, it takes 32 months to clear the debt.
FAQ
Why does the calculator round up? You can't make a partial final payment in practice, so months are rounded up to the next whole payment.
What if my payment never pays off the debt? If your monthly payment is less than or equal to the interest accruing each month, the balance grows and the debt is never repaid — the tool flags this.
Is this the snowball or avalanche method? This computes payoff time for one debt. The snowball/avalanche methods order multiple debts; this calculator handles each individual balance.
