Debt Payoff

How Avalanche And Snowball Payoff Are Calculated

The debt avalanche and debt snowball are the two standard strategies for paying off multiple debts at once, and they target them in a different order. Enter each debt’s balance, interest rate, and minimum payment, plus any extra amount you can put toward debt each month, and this calculator projects how long payoff takes and how much interest you’ll pay — for both strategies, side by side.

Avalanche always targets whichever debt has the highest interest rate first. It’s mathematically optimal: for the same total monthly budget, it always results in the least total interest paid, no matter how the debts are arranged.

Snowball always targets whichever debt has the smallest balance first. It usually costs more interest overall than Avalanche, but clearing an entire debt sooner — even a small one — is a real motivational win that helps some people stick with a payoff plan longer than the mathematically “better” method would.

Whichever method you pick, every debt still gets at least its own minimum payment every month. Your extra monthly amount (plus the minimum payments freed up from any debt you’ve already paid off) all goes toward whichever debt the strategy currently targets, then rolls over to the next one once that debt hits zero.

The Formula

Each month, for every debt still owed:

$$\vC{\text{Interest}} = \vA{\text{Balance}} \times (\vB{\text{Annual Rate}} \div 12)$$ $$\text{Balance} = \vA{\text{Balance}} + \vC{\text{Interest}} - \vD{\text{Payment}}$$

Every open debt receives at least its own minimum payment. Any extra budget — plus minimum payments freed up from already-paid-off debts — is applied to the current target debt (highest rate for Avalanche, smallest balance for Snowball), and rolls over to the next target the moment the current one reaches zero.

Worked Example

Three debts — a $4,000 credit card at 22% ($100 minimum), a $1,500 card at 18% ($50 minimum), and a $6,000 personal loan at 9% ($150 minimum) — with $200 extra paid every month:

1. Avalanche targets the 22% card first, then the 18% card, then the 9% loan.
2. Snowball targets the $1,500 card first (smallest balance), then the $4,000 card, then the $6,000 loan.
3. Avalanche always finishes with equal or lower total interest than Snowball for the exact same debts and the exact same extra payment — see your own numbers above for the size of that gap.

Key Factors to Consider

• The gap between avalanche and snowball narrows when interest rates are similar across debts. If every debt carries roughly the same rate, the order barely matters mathematically, and snowball’s motivational benefit comes at little to no real interest cost — the avalanche advantage grows specifically when rates differ significantly between debts.
• Behavioral consistency often matters more than the mathematically optimal strategy. Research on debt payoff behavior has found that people using the snowball method sometimes stick with their plan longer than those using avalanche, because clearing a whole debt (even a small one) provides a psychological win — the “best” strategy is ultimately the one you’ll actually follow through on.
• New debt added during the payoff period isn’t modeled by this calculator. This projection assumes no new charges or new debts are added while paying down the existing list — continuing to add debt undermines the whole plan regardless of which strategy is chosen.
• A variable-rate debt (like many credit cards) can see its rate change during the payoff period. This calculator assumes each debt’s entered rate stays constant for the whole payoff — a real rate change (up or down) would shift the actual results from what’s projected here.

Common Mistakes

• Entering an unrealistically low minimum payment. A minimum payment that doesn’t even cover the interest accruing each month means that debt’s balance never actually shrinks — this is exactly what produces the “Never within 50 years” result. Double-check each minimum against a real statement before assuming the projection is wrong.
• Comparing only the payoff date, not the total interest. Two strategies can finish only a month or two apart while differing by hundreds or thousands of dollars in total interest paid — always check both figures side by side, not just whichever one sounds more exciting.
• Switching strategies partway through. Jumping between avalanche and snowball mid-plan (chasing whichever looks better that month) usually costs more overall than picking one and sticking with it — the “rolled-over minimum payments” mechanic that makes both methods speed up over time depends on consistently targeting debts in the same order.

Useful to Know

Both methods use every dollar you have toward debt exactly the same way — the only real difference is the ORDER debts get targeted in. Avalanche is never worse mathematically, but the gap between the two shrinks toward zero as your debts’ interest rates get closer together, and grows as they spread further apart. If your debts already carry similar rates, picking whichever method (or order) feels more motivating costs you little to nothing in extra interest.