THE NUMORIX GUIDE
How to use the Debt Snowball Calculator
Last reviewed September 14, 2026
What this calculator does
The engine filters to debts with positive balances and minimum payments, sorts them by ascending balance, and simulates one month at a time.
Formula and method
The engine filters to debts with positive balances and minimum payments, sorts them by ascending balance, and simulates one month at a time. Each debt first accrues monthly interest at annual rate/12; the smallest active balance receives its minimum plus the entered extra payment, while later debts receive their minimum and any payment freed by a debt that closed. The loop stops at payoff or 600 months.
Variables and inputs
For each debt enter a name, balance, annual Rate, and Min Payment. Add Extra Monthly Payment as a separate dollar amount. The UI starts with two credit cards and a personal loan, allows rows to be added or removed, and uses the smallest current balance as the snowball target.
Worked example
With a $3,000 card at 20% and a $60 minimum, a $5,000 card at 18% with a $100 minimum, and an $8,000 loan at 10% with a $200 minimum, plus $200 extra, month-one interest is $50, $75, and $66.67. The first card receives $260 and ends near $2,790; the second receives $100 and ends near $4,975.
How to interpret the result
The result reports months to payoff, total payments, total interest, and a month-by-month schedule when the schedule is short enough to display. Sorting by the smallest balance is intended to create quick psychological wins; it is not necessarily the lowest-interest strategy.
Common mistakes to avoid
Enter annual APR-style rates such as 20, not monthly rates. Keep minimum payments positive and attached to the correct debt. Do not assume extra money will be applied by a lender to the balance you intend without checking account instructions, and do not confuse snowball order with avalanche order.
Assumptions and limitations
The simulation uses simple annual-rate/12 monthly interest, fixed minimum payments, no new charges, no fees, and no rate changes. It does not model promotional APRs, late fees, taxes, or credit reporting, and it imposes a 600-month ceiling. A real creditor can apply payments in a different order.