Debt Avalanche Calculator

Background.

Suppose you can find $300 a month beyond your minimum payments, and three debts are competing for it: a credit card at 24%, a store card at 9% and a car loan at 6%. The avalanche answer is blunt. Every spare dollar goes to the 24% card until it is gone, whichever balance happens to be smallest, because a dollar of card balance costs 2 cents of interest a month while a dollar of car loan costs half a cent.

You enter up to three debts, each with its balance, annual rate and minimum payment, plus the extra amount you can commit every month. The calculator then plays the plan forward a month at a time: interest is added to each balance, every minimum is paid, and the extra goes to the highest-rate debt. When that debt is cleared, its minimum payment joins the extra, so the sum aimed at the next debt grows each time one falls. It reports how many months the whole plan takes, how much interest you pay along the way, and the order in which the debts are finished.

Run those three debts through it — $6,000 on the card with a $180 minimum, $800 on the store card at $40, $9,000 on the car at $250, and $300 extra — and everything is cleared in 23 months for $1,731.24 of interest. Ordering the same payments by smallest balance instead, the debt snowball, also takes 23 months but costs $1,838.51. The $107.27 difference is what the snowball charges for its early win: it closes the store card in month 3, while the avalanche closes nothing until the card goes in month 15.

The model keeps rates and minimum payments fixed, assumes no new spending on the accounts and every payment on time. If one of those changes — a promotional rate ends, a card goes back into use, a lender resets a variable rate — run it again with the new numbers.

What is debt avalanche calculator?

The debt avalanche is a repayment order rather than a financial product. You keep every account current at its minimum and send all the extra money you have to the debt with the highest annual percentage rate. When that debt is paid off, its minimum and the extra move together onto the next-highest rate, and so on down the list. If two debts share a rate, the smaller balance goes first, since clearing it frees a minimum payment sooner. The debt snowball uses the same rollover but orders debts from smallest balance to largest. With the same monthly budget the two often finish in the same month or close to it; the avalanche pays less interest whenever the order by rate differs from the order by balance, and the two plans are identical when it does not.

How to use this calculator.

1. 01Take each debt's balance, APR and required minimum payment from its most recent statement. On a credit card, use the purchase APR from the interest-charge section; if part of the balance sits at a promotional rate, enter the rate that will apply for most of the time you expect to be paying it down.
2. 02Fill in Debt 1 first. It is the only required debt, and its balance and minimum must be above zero. Debts 2 and 3 are optional — a balance of 0 leaves that slot out entirely — and the order you type them in does not matter, because they are sorted by rate before anything is calculated.
3. 03Give each debt a recognizable name. Names do not affect the arithmetic; they are only used to report which account is finished first.
4. 04Enter as the extra monthly payment the amount above all the minimums combined that you can pay every month without fail. A figure you can only manage some months will make the plan look faster than it will be.
5. 05Read the months to debt-free and the total interest, then try a different extra amount. The change in total interest between two runs is what that extra money saves you.

The formula.

Each simulated month runs in three steps. First, interest: every open balance grows by its annual rate divided by 12, so $2,000 at 12% picks up $20. Second, minimums: each debt receives its minimum payment, or its whole balance if that is smaller. Third, the extra: the extra payment, plus the minimums of debts already finished, goes to the open debts in rate order, highest first. If it more than covers that debt, the remainder spills to the next debt in the same month. Any debt that reaches zero in a month is closed that month, whether its own minimum or the extra cleared it, and from the following month its minimum is added to the extra. The loop repeats until every balance is zero. The number of months it ran is the first result; the sum of all the interest it added is the second.

Why highest rate first? Take two debts with monthly rates r₁ greater than r₂. A dollar of principal removed from the first stops r₁ of interest every month it would otherwise have stayed; the same dollar on the second stops only r₂. Moving a dollar of payment from the higher-rate debt to the lower one therefore costs r₁ − r₂ for every month the difference lasts — on a 24% card against a 6% car loan, 1.5 cents per dollar per month. The same swap argument applies to any pair, which is why no other ordering of the same payments pays less interest while rates and payments stay fixed.

Two simplifications are worth knowing. Card issuers usually charge interest daily on the average daily balance, whereas this model adds a whole month's interest to the balance before the payment, so expect differences of a few cents from your statements. And each minimum stays at the figure you enter: real card minimums shrink as the balance falls, so the timeline only holds if you keep paying at least the original amount.

Debts do not have to be finished in rate order. A lower-rate debt whose own minimum payments clear it before the extra money reaches it is closed as soon as it hits zero, and its minimum is redirected to the highest-rate debt from the next month. Take $6,000 at 24% with a $180 minimum and $300 at 5% with a $100 minimum, plus $200 extra: the small debt is gone in month 4 by its minimum alone, the large one in month 16, and the payoff order shows the small debt first.

A worked example.

Frequently asked questions.

References& sources.

1. [1]FTC (2025). "How To Get Out of Debt."
2. [2]CFPB (2024). "How does paying down a mortgage work?"
3. [3]CFPB (2023). "How should I use lender credits and points (also called discount points)?"
4. [4]CFPB (2024). "What is a credit report?"
5. [5]myFICO (2024). "What's in my FICO Scores?"