Debt Snowball Calculator

What this calculator does

See when you'll be debt-free and how much interest you'll pay along the way. When you owe money in several places, a payoff plan turns a pile of separate bills into one clear order. You set a fixed monthly budget and pay the minimum on everything. Every spare dollar goes to one target debt. When that debt is gone, its payment rolls onto the next one. So the amount aimed at each target keeps growing, like a snowball rolling downhill.

The two common orders differ only in which debt goes first. The snowball method starts with the smallest balance. That gives quick wins that many people find motivating. The avalanche method starts with the highest APR, the yearly interest rate, which usually saves the most interest. This calculator runs your chosen method month by month. It also runs the other one, so you can see what your choice costs or saves.

Where it's used

Why this math matters outside the classroom:

• Ordering debts. The snowball method pays the smallest balance first, while the avalanche method pays the highest interest rate first.
• Monthly interest. A $1,000 balance at an 18% APR adds about $15 of interest in a month, which the payment must cover before the balance falls.
• Rolling payments. When one debt is paid off, its payment is added to the next debt on the list, so later debts are cleared faster.
• Comparing methods. Households run both orders on the same debts and budget to compare total interest and the payoff date.

How to use it

1. Choose snowball (smallest balance first) or avalanche (highest APR first).
2. For each debt, enter the balance, the APR and the minimum monthly payment. Leave the balance blank for any slots you don't need.
3. Enter any extra amount you can pay each month on top of all the minimums.
4. Read how many months until you're debt-free and the total interest. Then compare with the other method and check the payoff order table.

What the inputs mean

Payoff method

Snowball sorts by starting balance, smallest first. If two balances tie, the higher APR goes first. Avalanche sorts by APR, highest first. If two APRs tie, the smaller balance goes first.

Debt 1 minimum payment

Enter the minimum as a fixed dollar amount, such as the figure on your latest statement. It stays in the budget after the debt is gone.

Extra paid each month

Money beyond the minimums. Even a small extra amount speeds things up, because it all goes to one debt at a time.

Formula and method

budget = sum of all minimum payments + extra
each month, for each debt: balance = balance × (1 + APR ÷ 100 ÷ 12)
pay every open debt its minimum (or what is left on it)
send the rest of the budget to the first open debt in the payoff order, then the next
debt-free when every balance reaches zero; total interest = interest added to all debts

In the formulas, APR is each debt's yearly interest rate, and the budget is the total you pay every month. Each month, a debt is charged interest at its APR divided by 12, because there are 12 months in a year. Then the payments go in.

The budget never changes, and that's the whole trick. When a debt is paid off, you don't spend its minimum somewhere else. You add it to the payment on the next target.

The order is set at the start, from the starting balances or APRs. Running both orders on the same debts and budget shows the trade-off clearly. Avalanche normally costs less interest, while snowball usually pays off the first debt sooner.

Worked example

You have a $4,800 card at 24.9% (minimum $120), a $650 store card at 19.9% (minimum $25) and a $7,200 car loan at 6.9% (minimum $210). You can add $250 a month.

1. Budget: $120 + $25 + $210 + $250 = $605 a month.
2. Snowball order: the $650 store card, then the $4,800 card, then the car loan.
3. The store card is cleared in month 3, the larger card in month 17 and the car loan in month 24.
4. Interest on each: $19.12 + $1,012.34 + $656.68 = $1,688.14.
5. Avalanche on the same debts pays the 24.9% card first and costs $1,649.53, which is $38.61 less.

Result: Both methods are debt-free in 24 months. The snowball gets its first win in month 3 and costs $1,688.14 in interest. The avalanche costs $1,649.53, but its first payoff doesn't come until month 16.

Understanding the result

If the interest difference between the methods is small, choose the order you're most likely to stick with. It's often small when the APRs are close. A plan you follow beats a slightly cheaper plan you give up on.

If the difference is large, it's usually because one high-rate debt is also large. Then the avalanche order is worth considering. Try a bigger extra payment too. It shortens every timeline and shrinks the gap between the two methods.

Assumptions and limitations

• Interest is charged monthly at each debt's APR ÷ 12. There are no new charges, fees or rate changes.
• Minimums are fixed dollar amounts. The total monthly budget stays the same until everything is paid.
• The payoff order is set from the starting figures and doesn't change during the plan.
• Amounts aren't rounded to the cent.
• It doesn't handle card minimums that shrink as the balance falls, promotional rates or balance transfers.
• Loans with fixed schedules, such as car loans, normally can't take less than their set payment. They may also handle extra payments differently.
• This is a planning estimate, not advice on which debts to pay first in your situation.

Frequently asked questions

How this calculator is checked

Method: Month-by-month simulation with a fixed total budget (sum of minimums + extra), interest at each APR ÷ 12, minimums first and the remainder to debts in snowball (balance ascending) or avalanche (APR descending) order. The calculation is covered by automated tests with known reference values and edge cases. Last updated 2026-10-18. Found a problem? Tell us.

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