Debt payoff calculator: avalanche, snowball, and what the order actually costs
Most debt calculators ask for one balance and one payment and hand back a date. That's not the problem
anyone actually has. Real debt comes in three or four pieces at once — a card, a car, a student loan,
maybe a medical bill — each with its own rate and its own minimum, and the interesting question is
which one to attack first with whatever is left over at the end of the month.
This planner simulates that month by month rather than reaching for a formula, because once you have more
than one debt there isn't a formula. Interest accrues on each balance, minimums come out, and everything
left over goes to whichever debt sits first in your chosen order — spilling straight to the next debt
in the same month once one is cleared, so no payment is left idle. Your total monthly payment stays flat
across the whole plan, which is the actual mechanism behind both the debt avalanche and the
debt snowball: a cleared debt's payment rolls forward onto the next one instead of quietly
returning to your spending.
To use it: list each debt with its balance, interest rate, and minimum payment, then set how much extra you
can put toward debt each month. Pick avalanche (highest rate first) or snowball (smallest balance first) and
the tool shows your debt-free date, the total interest you'll pay, and how both compare against doing
nothing differently. The comparison line tells you what choosing one order over the other is worth in real
dollars on your numbers — which is the only way to know whether the snowball's motivational advantage
is costing you fifty dollars or five thousand.
Frequently asked questions
What's the difference between the debt avalanche and the debt snowball?
Both put every spare dollar toward one debt at a time while paying minimums on the rest — they only disagree about which debt goes first. The avalanche targets the highest interest rate, which always costs the least in total interest. The snowball targets the smallest balance, which clears individual debts sooner and gives you visible wins earlier. This planner runs both on your actual numbers and tells you exactly what the difference is worth.
Which one saves more money?
The avalanche, always — mathematically it can't lose, because it kills the most expensive interest first. The real question is by how much. Sometimes the gap is a few hundred dollars over several years, in which case the snowball's motivational advantage is worth more than the difference. Sometimes it's thousands. The comparison line in the tool tells you which situation you're in rather than leaving it as a rule of thumb.
How much extra should I put toward debt each month?
Whatever you can hold consistently, after an emergency buffer and any employer retirement match. The number matters less than the consistency: this planner assumes your total payment stays flat, so when one debt clears, its payment rolls onto the next one instead of drifting back into spending. That rolling-forward effect is what makes the last debts fall much faster than the first.
Should I pay off debt or invest first?
As a rough guide, debt above roughly 7–8% interest is very hard to beat with investment returns, so paying it down first is usually the stronger move; below that, the answer depends on your rate, your expected return, and your tolerance for carrying a balance. High-rate credit card debt is rarely a close call. For the specific case of a mortgage, where the rate is usually low and the balance large, try the Mortgage Payoff vs. Invest calculator instead.
Why does paying only the minimum take so long?
Because most credit card minimums are a percentage of the balance — typically around 2%, with a small dollar floor. As the balance falls, so does the required payment, so the payoff stretches out for decades and most of what you pay is interest. Set a debt's minimum to “% of balance” on the Advanced tab and compare against a fixed extra payment to see the size of that effect on your own numbers.
Can a balance grow even while I'm paying it?
Yes, and the planner flags it when it happens. If a minimum payment is smaller than the interest that debt accrues each month, the balance rises no matter how faithfully you pay. That's called negative amortization, and it's why this tool will tell you plainly that a plan never clears rather than quietly showing an unrealistically distant payoff date.
Does the planner handle bonuses or a raise partway through?
It does. One-off lump sums — a tax refund, a bonus, a gift — can be scheduled in any month on the Intermediate tab, and they land on top of that month's payment. The Advanced tab adds planned changes to your monthly extra, so you can model a raise arriving next spring or a car payment elsewhere ending in eighteen months.
Is my debt information stored anywhere?
No. Everything you enter is saved only in your browser's local storage — nothing is sent to a server, and there's no account or sign-in. That also means it's only available on this browser and device; use the dashboard's “Export all” button any time you want a backup file you can restore later or move to another device.
