Debt Snowball Calculator

What this calculator does

When you owe money in several places at once, the hardest question isn’t whether to pay extra — it’s where. This calculator simulates your entire debt payoff month by month under the two standard strategies, using your real balances, rates, and minimum payments. You get the payoff order, the month each debt dies, your debt-free date, and total interest — for both strategies — so the snowball-versus-avalanche debate becomes a comparison of two concrete numbers instead of two philosophies.

Add or remove debt rows to match your situation exactly; the simulation updates instantly.

How the math works

Every month, the simulation does what a disciplined borrower would do:

1. Interest accrues on each balance: interest = balance × (APR ÷ 12).
2. Minimum payments are made on every debt.
3. The extra budget attacks one target — the smallest balance (snowball) or the highest APR (avalanche).
4. Rollover: when a debt reaches zero, its minimum payment joins the extra budget permanently. This is the “snowball effect” both methods share — your attack power grows with every debt you eliminate.

There is no closed-form formula for multi-debt payoff; the calculator runs the actual month-by-month simulation, the same way your balances will actually behave.

A worked example

Consider the calculator’s default scenario: a $6,500 credit card at 24.9% APR (min $130), an $11,000 car loan at 7.5% (min $260), and an $1,800 medical bill at 0% (min $50), with $200 extra per month.

The snowball attacks the medical bill first — it’s the smallest — and clears it quickly, rolling its $50 minimum into the attack. The avalanche goes straight at the 24.9% credit card, because every month that balance survives costs about $135 in interest (6,500 × 24.9% ÷ 12) versus roughly $69 for the car loan and nothing for the medical bill. Run the comparison and you’ll see the pattern that holds for almost any debt mix: the avalanche finishes with less total interest, and the snowball delivers its first eliminated debt sooner. The size of the gap depends entirely on how far apart your interest rates are.

Practical tips

1. Stop the bleeding first. A payoff plan only works if the balances stop growing — pause new charging on the cards you’re attacking, or the simulation here will always be optimistic.
2. Automate the minimums, manualize the attack. Set every minimum on autopay so a missed payment never derails the plan, then make the extra payment manually each month — the act of doing it sustains motivation.
3. Rerun after every payoff. Each eliminated debt changes the picture. A quick recheck confirms the next target and shows your improving debt-free date, which is powerful reinforcement.
4. Negotiate rates before you attack. A single phone call asking a card issuer for a lower APR — or moving a balance to a 0% intro transfer offer with a fee you’ve priced — can save more than months of optimized ordering. Update the rates here and watch the totals move.

Why the rollover matters more than the order

People argue endlessly about snowball versus avalanche, but both share the mechanism that does most of the work: payments never shrink. As each debt disappears, its minimum joins the attack budget, so your final debt absorbs the entire monthly amount you started with. That is why consolidating your effort beats spreading extra money thinly across all balances — a strategy this calculator will happily show you the cost of, if you compare it by setting the extra budget to zero and mentally spreading it around. Focus wins.