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Debt payoff calculator: avalanche vs snowball

This is for anyone with two or more debts who wants to see what each payoff order would do with the same monthly budget. Type your own numbers. The result updates as you type, and nothing leaves your device. It is general information, not financial advice.

Worked example (shown when scripts are off): one debt of $1,000 at 12 percent APR with a $100 payment each month is paid off in 11 months. Interest each month is 1 percent of the balance, so the last payment is a little smaller than $100.

Before you decide

The example numbers above are made up, so replace them with figures from your statements. The calculator ignores late fees, new purchases, promotional rates that end, and changes to variable rates. If you are behind on payments or contacted by collectors, a nonprofit credit counselor or a legal aid office can look at your whole situation.

How the calculator works

Each month the calculator adds interest to every open debt. Interest is the balance times the annual rate divided by 12. Then it pays every debt its minimum. Your total monthly budget is the sum of all the starting minimums plus your extra amount, and it stays the same for the whole plan. Whatever is left after the minimums goes to one debt, chosen by the order you are comparing. When a debt is cleared, the minimum you were paying on it stays in the budget and rolls onto the next debt.

The two orders differ only in which debt gets the leftover money. Avalanche sends it to the highest interest rate first. Snowball sends it to the smallest balance first. Both are described this way by the Consumer Financial Protection Bureau, which also notes that the highest-rate method usually costs less interest while the smallest-balance method gives quicker visible wins.

Reading the result

Look at three numbers for each order: months until every debt is gone, total interest, and the order the debts clear. In this model, with a fixed monthly budget, avalanche does not pay more interest than snowball, and the gap is often small when the rates are close together or the smallest balance is also the highest rate. If the gap is small, the better plan is the one you will actually keep following.

The number of months is a simulation, not a promise. A $100 change in the extra amount can move the finish date by many months, so try a few amounts. If the page says the payments do not clear the debt, the monthly interest is at least as large as what you are paying, and the plan needs a bigger payment or a different approach.

A worked example

Take a $1,000 balance at 12 percent APR and a $100 payment. The monthly rate is 1 percent. After month 1 the balance is $1,000 plus $10 of interest minus $100, or $910. Repeating that for 11 months leaves a final payment of about $59 instead of $100, and total interest comes to about $59. The calculator runs this same loop for all your debts at once.

Limits

Interest here is a simple monthly estimate. Real lenders may compound daily, round differently or charge fees.
Rates are treated as fixed. Variable rates and ended promotional rates will change the real result.
It assumes you add no new debt and never miss a payment.
It cannot tell you whether to build savings first. See the guide on that question below.
It is general information, not financial, tax or legal advice.

Where this comes from

The two payoff orders follow how the Consumer Financial Protection Bureau describes them in its blog post on reducing debt and its reducing-debt worksheet from the Your Money, Your Goals toolkit. The monthly interest and balance update is the standard amortization arithmetic. The tests check the code against a hand-worked single-debt example, a zero-interest case and a grid of inputs.