Debt Payoff Calculator: Avalanche vs Snowball Months (Free)

This calculator runs entirely in your browser: nothing you type is uploaded, stored or sent anywhere, and it keeps working with the connection off. Enter each debt with its balance, its APR and the minimum the lender asks for, add whatever you can put on top each month, and it plays the whole repayment forward twice. Once paying the highest rate first, once paying the smallest balance first. For each order it returns the number of months until every balance reaches zero, the total interest paid along the way, and the order the debts would be attacked in. Underneath, one line names the cheaper strategy and the difference in interest between them, which is usually smaller than people expect.

How to use it

1. The currency symbol is only used to print the results. Type the one you think in and enter every figure in that same currency.
2. List your debts, one per row, four rows available. Each takes a name, the balance you owe today, the APR and the minimum payment. Use the names you would recognise on a statement rather than categories, because the payment order table prints them straight back at you. A row with a balance of zero is skipped, so three debts and one empty row is perfectly normal.
3. In the rate column, put the APR and not the monthly rate. Statements usually show an annual figure, sometimes as a purchase rate and sometimes as a representative APR. Put the annual number in and the calculator divides by twelve.
4. The extra payment is what you can add on top of all the minimums each month. Zero is a valid answer and worth typing first, because minimums-only is the baseline everything else gets measured against.
5. Now read both panels. Left is highest rate first, right is smallest balance first, each with the time to clear everything and the interest paid getting there. The line beneath names the cheaper order and the gap between them, and the final table lists the debts in the order each strategy would attack them.

Avalanche versus snowball

These are the two orderings the calculator compares, and the argument between them is one of the few genuinely interesting questions in personal finance, because arithmetic and behaviour point in different directions.

The case for highest rate first, the avalanche, is arithmetic and is not really debatable. Interest accrues on every open balance at its own rate. Any euro you direct at one debt does the most work where the rate is highest, because that is where the balance grows fastest between payments. Kill the most expensive growth first. Over the life of the plan that cannot cost more than any other order, and it usually costs less.

The case for smallest balance first, the snowball, is about whether the plan survives at all. A small balance clears quickly, sometimes within a month or two. An account closes. A statement stops arriving. The list gets shorter, and that is a visible result at the exact point where the interest saving from a better order is still invisible. Published research backs the intuition up: a 2012 study in the Journal of Marketing Research found that the number of accounts closed, rather than the share of total balance repaid, predicted whether people stayed with a repayment programme, and later work in the Journal of Consumer Research in 2016 found that concentrating repayment on a single account raised motivation to keep going. None of that repeals the arithmetic. It just points out that the arithmetic only pays out if you are still making the payments in month twenty.

Most of the time this is a small decision. With the three debts the calculator loads by default, the difference is about 57 in interest across 29 months. Real money, and also less than one of the minimums. When the rates sit close together, or the two orders happen to agree, the gap shrinks to nothing and the calculator says as much. When one debt carries a far higher rate than the rest, the gap widens into the hundreds or thousands. So do not guess. Put your own numbers in and read the line. Small difference, take the order you will keep to. Large difference, let the arithmetic win.

There is also a third order the calculator cannot model, and it matters more than either of these. Some debts carry consequences beyond interest: rent or mortgage arrears, council tax, energy bills, court fines, anything secured on your home or your car. Debt advice charities call these priority debts and put them ahead of everything else regardless of the rate, because the cost of not paying them is not measured in interest. If any of your rows is one of those, the rate column is the wrong way to rank it.

What the simulation assumes

The model is deliberately simple, and it is worth knowing exactly what it does before you trust the date it prints.

It works in whole monthly periods. Each month, in order: it adds interest to every open balance at the APR divided by twelve, then it pays each open debt's minimum in the strategy's order, then it throws every remaining cent of the budget at the first open debt in that order. A payment is never larger than the balance it is paid against, so the leftover simply moves down the list.

The budget is the sum of every minimum you entered plus the extra payment, and it does not change as debts close. That single assumption is where the word snowball comes from. When the overdraft clears, the 25 that used to service it is still inside the budget, so it lands on the next debt along with the extra payment. By the final debt you may be paying several times its own minimum every month, which is why the last balance falls far faster than the first.

Ordering is mechanical. Avalanche sorts by APR descending, with the smaller balance breaking a tie. Snowball sorts by balance ascending, with the higher rate breaking a tie. The order is fixed at the start and does not re-sort as balances change.

If the total owed fails to fall in any single month, the simulation stops and reports that the plan never clears the debt. That is the case where the interest charged is at least as large as everything you paid, and no number of months will fix it. It also gives up after 600 months, which is fifty years and not a plan.

What it leaves out is the honest part. There are no fees of any kind: no annual fee, no late fee, no balance transfer fee, no insurance premium. Promotional rates are not modelled, so a zero percent period that expires in fourteen months and reverts to twenty-something will make the real cost higher than the figure here. Minimum payments are held constant, whereas most credit cards recalculate the minimum as a percentage of the balance, so it shrinks as you repay; holding it flat means the calculator is slightly optimistic about the minimums-only case and broadly right once an extra payment is doing the work. Rate changes are not modelled at all, so a variable rate that moves is not reflected. Interest is charged once a month on the balance rather than daily on the average daily balance the way most card issuers actually calculate it, which moves the total by a small amount in either direction. Finally, it assumes every payment is made, on time, every month.

Treat the output as a good comparison between two orderings and a reasonable estimate of the term, not as a statement from your lender.

One input error accounts for most of the odd results people report. In the minimum column they type what they actually pay each month rather than what the lender requires, then add their extra payment on top as well. The same money goes in twice, the term collapses, and the date looks wonderful. If the answer surprises you in a good way, that is the first thing to check. The minimum column is the lender's number, off the statement. The extra payment column is yours.

Where this stops being a maths problem

A payoff calculator is the right tool when you have some credit you want gone, something extra each month, and a question about order and timing. For other situations it is the wrong tool, and it is worth saying which is which.

The first is a minimum that barely covers the interest. Enter a high rate balance with a minimum close to the monthly interest charge and you get either a term of two hundred months or the message that the balances never clear. That is not a rounding artefact. It is the arithmetic of revolving credit working exactly as designed, and the CFPB's guidance on how card interest is calculated explains the mechanism plainly. If that is your result, a different repayment order is not the useful next step.

Payday and other high-cost short-term lending is the second. The APR field will happily accept a rate in the hundreds and the simulation will dutifully produce a number, but a product designed to be rolled over is not really described by a monthly amortisation model. Treat anything this page prints about it as an illustration.

Arrears and defaults are the third. Once an account has broken down, the numbers on a statement stop describing what actually happens next: charges, collection activity, default notices and court action all follow their own rules, and priority debts carry consequences no interest rate captures. A calculator is not equipped for any of it.

And sometimes the total simply does not work. If the minimums exceed what is left after essential living costs, no ordering of the payments will help.

In all of those cases the right person is a free, regulated debt adviser, and the important word is free. In the UK, National Debtline and StepChange both give free advice, and Citizens Advice does too. In the US, the non-profit member agencies of the National Foundation for Credit Counseling offer free or low-cost counselling. Most EU countries have a national equivalent, usually run by a consumer body or a recognised charity. They will look at your income, your essential costs and every debt at once, including the ones with consequences beyond interest, and they can explain options that are not visible from a spreadsheet. There is nothing to be embarrassed about in making that call, and there is no reason to pay a company for something a charity does for nothing.

This page does not give personal financial advice, does not recommend any lender, consolidation loan or balance transfer, and cannot see your circumstances. It does arithmetic, which is a genuinely useful thing and a strictly limited one.

Three sets of numbers

Start with the three debts the calculator loads by default: a credit card of 2,400 at 19.9 percent with a 60 minimum, a personal loan of 6,000 at 7.5 percent with a 180 minimum, and an overdraft of 800 at 14 percent with a 25 minimum. The extra payment is 100, making the budget 365 a month. Highest rate first goes card, overdraft, loan, and clears everything in 29 months for 1,192 in interest. Smallest balance first goes overdraft, card, loan, and also clears in 29 months, for 1,249. So the verdict line reads that highest rate first saves 57. Both orders land in the same month because the budget is fixed and the difference disappears inside the final part month.

Now set the extra payment to zero. The budget falls to 265, the minimums alone. Both strategies take 44 months and both cost about 2,246 in interest, a gap of well under one unit, so the calculator says the two orders cost about the same. This is the example that matters. Finding 100 a month cuts fifteen months off the term and saves roughly 1,054 in interest, which makes the 57 the ordering was worth look like what it is. The extra payment is the decision. The ordering is a tie-breaker.

The order does earn its keep sometimes. A card of 3,000 at 26 percent with a 60 minimum, a small loan of 900 at 9 percent with a 20 minimum, and 40 extra, so a budget of 120. Highest rate first clears in 50 months for 2,097 in interest. Smallest balance first clears in 55 months for 2,596. That is a gap of 499 and five months, because one debt carries nearly three times the rate of the other and the snowball spends its early months on the cheap one. When the numbers look like this, let the arithmetic win.

Finding the extra payment

Every example above says the same thing in a different way: the extra payment is where the leverage is. A hundred a month beats any clever ordering, and the question that actually decides your payoff date is where that hundred comes from. That is a spending question, not a debt question, and it is the one Cash Book is built for.

The app has no debt feature, no payoff countdown and no bank connection, and it will not import a balance from a lender. What it has is a fast way to log what you spend and an honest picture of where it went. Insights shows the month against the one before it and names the tags where the change happened, which is usually where a spare hundred is hiding. A per-tag budget turns a decision to cut something into a thin progress bar you see every day rather than a promise you made once.

Accounts hold balances for cash, cards and savings, with one net-worth number over all of them. That figure is the closest the app comes to tracking a payoff: as the card balance you keep there falls, the total moves. Entering balances is manual, because Cash Book never connects to a bank, and the net worth calculator does the same arithmetic in a browser.

All of it depends on logging happening at all, which is why voice logging matters more here than it looks: a purchase you do not record is a purchase you cannot cut. For the routine around it, how to make a monthly budget that sticks covers where a repeatable extra payment comes from, how to track subscriptions and recurring bills finds the recurring lines that most often become one, and how to stop impulse buying is about the purchases that quietly replace it. If most of your spending leaves as notes and coins, how to track cash spending is the starting point instead.

Two other tools pair with this one. The 50/30/20 budget calculator gives a rough ceiling for what debt repayment and saving can take from take-home pay, and the subscription cost calculator adds up the recurring charges that are the easiest source of an extra payment. Before the extra payment goes entirely to debt, the emergency fund calculator is worth a minute, because a small cushion is what stops the next unexpected bill going straight back onto the card. The glossary entries on cash flow and the emergency fund cover the two ideas underneath all of this.

Put your own four rows in, read the months, then change the extra payment by twenty and read them again. The second number is the one worth working on.

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Get Cash Book on the App StoreFree for 7 days. $19.99 once for lifetime.