Debt Avalanche Calculator

• Highest APR first. Mathematically optimal: no ordering pays less interest at the same total payment.
• Shows the payoff order, per-debt interest cost, and the projected debt-free date.
• Compares directly against the snowball and against minimum payments only.
• The catch is honest and stated: the first debt can take a long time to clear, and that is where plans fail.

Why highest-rate-first is provably cheapest

Interest accrues on each balance independently. A dollar sitting on a 27.5% card costs about 2.29 cents a month; the same dollar on a 5.5% student loan costs about 0.46 cents. Removing the expensive dollar avoids five times more cost.

Since every dollar of extra payment must go somewhere, and each dollar removes future interest at exactly the rate of the debt it is applied to, total interest is minimised by always applying it to the highest rate available. That holds regardless of balance sizes, and it is why the avalanche cannot be beaten on cost.

Monthly interest cost of $1 of balance = APR ÷ 12 ÷ 100

  27.5% card         → $0.0229 per month
  23.9% card         → $0.0199 per month
   7.4% car loan     → $0.0062 per month
   5.5% student loan → $0.0046 per month

Balance size does not enter the calculation at all. A $500 balance at 29% is more urgent, per dollar, than a $30,000 balance at 6% — even though the second is sixty times larger and feels more pressing.

The rollover: why the last debts vanish quickly

Like the snowball, the avalanche never lets the payment shrink. When a debt clears, its minimum joins the extra payment and moves to the next target.

This produces an acceleration that surprises people partway through the plan. If you start with four debts and $300 of extra payment, you might be sending $355 at the first target. By the time you reach the last one, the same total outgoing might be directing $1,100 at a single balance. Progress that felt glacial in year one becomes rapid in year three, and this is exactly the point at which many people, having nearly finished, could reasonably conclude the method was working all along.

Your results table shows the exact date each debt clears, which makes the acceleration visible before you experience it — worth looking at when the first target is a large balance and progress feels slow.

The honest catch

The avalanche's weakness is not mathematical. It is that the highest-rate debt is not always the smallest, and if it happens to be large, you can spend a year or more with no account closing and no visible milestone.

Debt payoff usually takes years, and the dominant failure mode is abandonment rather than misordering. A method that is 3% cheaper but 20% more likely to be abandoned is not actually cheaper. This is a real argument for the snowball, and it deserves to be taken seriously rather than dismissed.

Two practical middle paths:

• Clear one very small balance first, then switch to avalanche. You get the closure of an account in the first month or two, then run the optimal order for the rest. On most debt mixes this costs very little.
• Run the avalanche but track progress by total interest avoided rather than accounts closed. Your results show the interest saved against minimum payments — a number that grows every month even when no account closes.

Look at the comparison in your results before deciding. If the avalanche saves you $180 across four years, choose whichever method you will finish. If it saves $4,000, that is worth some discipline.

When rates are not fixed

The avalanche depends on knowing the rates. Several things make that harder than it looks:

• Variable-rate cards. Most credit card APRs are tied to the prime rate and move with it. A card that is second in your ordering today may become first.
• Promotional and deferred-interest offers. A 0% promotion is genuinely the lowest priority while it lasts — but deferred-interest offers, common in store financing, charge all the interest accrued since purchase if any balance remains when the promotion ends. Those should be treated as urgent regardless of the stated rate, and cleared before the deadline.
• Penalty APRs. A missed payment can move a card to a much higher rate, reshuffling the whole plan.

Re-running this calculator once or twice a year with current statement figures is enough to keep the ordering right.

What to do before starting either method

Capture any employer retirement match. A 50% match is an immediate 50% return, which beats clearing even a 29% card. Contribute at least enough to get the full match before redirecting anything to debt.

Build a starter cash reserve. Without one, the next car repair goes back on a card. A month of essential expenses is a common starting point, with the full reserve built after the expensive debt is clear. Size it with the Emergency Fund calculator.

Check for a lower rate. Before committing to years of 24% interest, it is worth an hour to see whether a balance transfer, a credit union personal loan, or simply asking your issuer for a rate reduction is available. Model any offer in the Credit Card Payoff calculator including its fee — some are worth taking and some are not.

Confirm the minimums are right. The plan depends on them. Take the figures from current statements rather than memory.

Common mistakes

Ordering by balance while believing you are running an avalanche. The two methods produce different orders whenever the largest balance is not the highest rate. Enter the actual APRs from your statements.

Letting the payment fall as balances drop. The rollover is where most of the speed comes from. If you allow the total monthly payment to shrink as accounts close, the plan takes far longer.

Ignoring a 0% promotion's end date. A promotional balance is correctly last in the avalanche order until the promotion expires — at which point it may jump to first. Diarise the date.

Adding new debt. The projection assumes none. It is the assumption most often broken.

Choosing the method rather than the payment. Doubling the extra payment changes the outcome far more than the choice between methods. If you are going to spend energy optimising something, spend it there.

Frequently asked questions