Loan Payoff Calculator

What "avalanche" and "snowball" actually change

When you owe money on several debts at once, the minimum payment on each one keeps the lenders happy but barely moves the balance. The real question is where your extra dollars go. Both the avalanche and snowball methods pay every minimum on time; they differ only in which single debt receives the leftover money each month. The avalanche directs that surplus to the debt with the highest interest rate, while the snowball sends it to the debt with the smallest balance. This calculator runs both simulations month by month — applying interest, then minimums, then your extra payment — so you can see the two timelines side by side instead of guessing.

How the month-by-month engine works

Each simulated month, the tool does three things in order. First, it charges interest on every remaining balance using the monthly rate, which is the APR divided by 12. A 19.99% card therefore accrues about 0.0199 / 12 ≈ 0.0167, or 1.67% of its balance, that month. Second, it subtracts each debt's minimum payment. Third, it takes your single pool of extra money and throws all of it at the first debt still owing in the prioritized order. When a balance hits zero, that debt's freed-up minimum effectively joins the pool for the next target — the "rolling" effect that makes both methods accelerate over time.

A worked example

Take the three debts the calculator loads by default: a $5,000 credit card at 19.99%, a $12,000 car loan at 6.5%, and an $8,000 student loan at 4.5%, with minimums of $100, $220, and $90. The avalanche orders them card → car → student (highest rate first). The snowball orders them card → student → car (smallest balance first). Notice the card happens to be both the highest rate and a mid-size balance, so both methods attack it first — but they diverge afterward, and that divergence is exactly where avalanche pulls ahead on total interest. Add even $100 in the extra-payment box and the "Extra Payment Savings" panel shows how many months and how many dollars of interest you avoid versus paying minimums alone.

Reading the results honestly

The avalanche almost always reports the lower "Total interest" figure, because it starves your most expensive debt first. The snowball often finishes a debt sooner — that first zeroed balance is a genuine morale boost, even if the math is slightly worse. The gap between the two is usually modest when your interest rates are close together and grows wide when one debt carries a punishing rate. If your card is at 24% and everything else is under 7%, avalanche can save real money; if all your debts sit within a few points of each other, pick whichever order you will actually stick to.

Practical tips

• Enter the true APR, not the monthly rate. The tool divides by 12 internally. Typing 1.67 instead of 19.99 will dramatically understate your interest.
• Use realistic minimums. Credit card minimums are often a small percentage of the balance, but this tool treats your minimum as a fixed dollar amount. Use a slightly conservative figure so the payoff date isn't rosier than reality.
• Test the value of every extra dollar. Run it at $0 extra, then $50, then $100. The non-linear jump in interest saved is the most persuasive reason to find a little more in your budget.
• Re-run after each windfall. A tax refund or bonus applied as a one-time chunk isn't modeled directly, but you can approximate it by temporarily lowering a balance and recalculating.

Common mistakes

• Closing a paid-off card and stopping there. The power of both methods comes from redirecting the freed payment to the next debt, not pocketing it.
• Chasing the snowball when one rate is extreme. A 0% promotional balance you snowball first while a 29% card festers is the classic trap; the avalanche column will show you the cost.
• Ignoring new spending. The simulation assumes balances only go down. If you keep charging the card, no payoff plan survives.

Privacy and limits

Every figure you enter is processed in your browser. The balances, rates, and the SVG chart never leave your device and nothing is sent to a server. Two limits are worth knowing: the engine caps the simulation at 600 months (50 years) to avoid an endless loop on an unpayable debt, and it applies all extra money to one debt at a time rather than splitting it. Both choices match how avalanche and snowball are meant to be run, but they mean the tool is a planning aid, not a substitute for your loan servicer's exact amortization schedule.