Debt Snowball vs. Avalanche Calculator

There are two sensible ways to attack multiple debts, and people argue about them constantly. The snowball clears your smallest balance first. The avalanche clears your highest interest rate first. This calculator runs both against your actual numbers so you can stop guessing which one is worth it.

What the calculator is doing

Each month it charges interest on every balance, pays every minimum, then throws whatever is left of your extra payment at one target debt. When a debt clears, its minimum rolls into the extra payment — that rolling effect is the "snowball", and it is why payoff accelerates rather than staying linear.

The only difference between the two methods is which debt gets targeted:

Which one should you pick?

Run both and look at the gap. That is the honest answer, and it is why the calculator shows you what switching would cost.

For most people the difference is smaller than expected — often a few hundred dollars across several years. If the avalanche saves you $80, the snowball is probably the better choice, because a method you abandon in month four saves nothing at all. If the avalanche saves you $2,000, that is real money and worth the slower start.

The one case where avalanche clearly wins is when you have a large balance at a very high rate — a maxed store card at 27% sitting alongside a modest car loan at 6%. There, targeting the small car loan first lets the expensive debt keep compounding.

Why the extra payment matters more than the method

The calculator shows a line for what your extra payment buys you, and it is usually the biggest number on the page. Moving from $0 extra to $150 extra typically cuts years off the schedule. Switching methods might cut months.

Put differently: how much you overpay matters more than which debt you overpay. If you only have energy for one decision, make it finding an extra $50 rather than optimising the order.

Reading the "not at this rate" result

If the calculator says you will not clear the debt, it means your minimum payments are barely covering the interest being charged. The balance is treading water or growing.

This is a genuinely difficult situation and not one a calculator solves. It is worth speaking to a non-profit debt advice service — they are free, they do not sell you anything, and they can often negotiate rates or arrange a plan that stops interest accruing. Do not wait until you have missed payments to make that call.

What this calculator does not include

• Fees — annual fees, late fees, and balance transfer fees are not modelled.
• Variable rates — it assumes your APR stays put, which credit card rates often do not.
• Promotional periods — a 0% intro rate that expires mid-schedule will change the result.
• Minimum payments that shrink — many cards calculate the minimum as a percentage of the balance, so it falls as you pay down. The calculator holds your minimum steady, which makes it slightly conservative.

Treat the payoff date as a good planning estimate, not a promise.

How this is calculated

Month by month, for every debt that still has a balance:

1. Interest is added: balance × (APR ÷ 100 ÷ 12).

2. The minimum payment is paid (or the whole balance, if it is smaller).

3. Your extra payment goes at one target debt. Snowball targets the smallest balance; avalanche targets the highest APR. A debt that is cleared frees up the unused part of its minimum that same month.

The calculator repeats this until every balance is zero or it reaches 600 months, and then reports the months taken, total interest and total paid.

Worked example (illustrative, hypothetical balances): Card A has $1,200 at 19% APR with a $40 minimum. Card B has $4,000 at 24% APR with a $100 minimum. The extra payment is $200 a month.

| Plan | Months to clear | Total interest | Total paid |

|---|---|---|---|

| Minimums only (no extra) | 81 | $4,522.00 | $9,722.00 |

| Snowball ($200 extra, Card A first) | 21 | $1,123.92 | $6,323.92 |

| Avalanche ($200 extra, Card B first) | 20 | $984.03 | $6,184.03 |

In this example both methods beat minimum payments by a wide margin, and avalanche costs $1,123.92 − $984.03 = $139.89 less interest and finishes a month sooner, because the higher-rate card is also the larger balance. Whether that gap is worth losing an early win is a personal choice. The totals above are $5,200 of starting balances plus interest, so total paid minus total interest equals $5,200 in each row.

Minimums are held constant, interest is calculated monthly from the stated APR, and fees, promotional rates and changes in rate are not modelled.

Read the full guide

For a step-by-step walkthrough of setting up a payoff plan and sticking with it, read our guide on the debt snowball method.