Partner Debt Payoff Strategy Calculator

This calculator runs a month-by-month simulation of two debts — not a closed-form formula — because debt payoff timelines depend on which balance receives extra payments each month, and that choice changes over time as balances shrink. Each month it accrues interest on both balances at their monthly rate (annual rate ÷ 12), applies each debt's minimum payment, then directs every dollar of your extra monthly payment toward whichever debt the chosen strategy targets: avalanche sends it to whichever debt currently carries the higher interest rate, snowball sends it to whichever has the lower current balance. Once the targeted debt is paid off, leftover extra rolls to the other debt automatically, and the simulation continues until both hit zero (capped at 600 months to avoid runaway loops on payments too small to cover accruing interest).

It runs the same simulation with minimum payments only as a baseline, then reports the difference in total interest and months as your savings from committing extra payments. Because avalanche always retires the mathematically most expensive debt first, it produces the lowest total interest of the two strategies whenever balances and rates stay fixed — snowball trades some of that interest savings for the psychological win of eliminating a balance sooner. A common mixup: this tool assumes fixed rates and payments for the whole payoff period, so it won't reflect promotional-rate expirations, balance transfers, or added debt along the way.