List what you owe, add whatever extra you can put toward debt each month, and compare the two standard payoff strategies side by side.
Credit cards, car loans, personal loans, student loans: anything with a balance, an interest rate, and a minimum payment. Starting example numbers below; replace them with your own.
Same debts, same total monthly payment either way, only the order changes. Debt avalanche always puts every extra dollar toward the highest interest rate first. Debt snowball always puts it toward the smallest balance first. A third option below skips the ordering question entirely: roll every debt into one new loan at a single rate, still paid with that same total monthly payment.
This calculator assumes interest compounds monthly on the current balance (balance × APR ÷ 12 each month) and that your total monthly debt payment stays constant until everything's paid off: a simplification of how real cards and loans compound, close enough for comparing strategies against each other. It doesn't account for promotional/introductory rates, balance transfer fees, or a rate that changes over time.
The avalanche pays the highest-rate debt first and costs the least interest; the snowball pays the smallest balance first and gives quicker wins. On many debt lists the two produce the same plan or nearly the same cost, and paying anything extra matters far more than which order you choose. Which debt do you pay first? has the numbers.
Enter it in the extra-payment box: the calculator applies it to the target debt each month and rolls every paid-off minimum into the next, then shows the new payoff date and interest for both strategies.
Only if its rate is meaningfully lower than the average rate on the debts it replaces and you do not run the old balances back up. The consolidation check compares a single loan at the rate you enter against paying the debts off as they are.