Verified calculation
Debt payoff calculator
See what the avalanche and snowball methods actually cost you, month by month, against doing nothing but the minimums.
The debts in this scenario
| Debt | Balance | Rate | Minimum |
|---|---|---|---|
| Store card | $900.00 | 29.99% | $30.00 |
| Credit card | $6,000.00 | 22.99% | $150.00 |
| Personal loan | $2,500.00 | 6.99% | $120.00 |
| Paying each month | $600.00 | ||
Your debts
What you can pay each month
Your minimum payments come to $300.00 a month.
What happens
How this was calculated
Each month, interest is charged on the balance you owed at the start of the month, then your payment is applied:
interest = balance × (annual rate ÷ 12)
new balance = balance + interest − payment
Every debt gets its minimum. Whatever is left of your monthly total goes to a single target debt — the highest rate under avalanche, the smallest balance under snowball. When a debt clears, its minimum joins the surplus, which is why the balance falls faster over time.
Month 1, in full:
| Debt | Opening | Interest | Payment | Closing |
|---|---|---|---|---|
| d1 | $900.00 | $22.49 | $330.00 | $592.49 |
| d2 | $6,000.00 | $114.95 | $150.00 | $5,964.95 |
| d3 | $2,500.00 | $14.56 | $120.00 | $2,394.56 |
| Month | Paid | Interest | Remaining |
|---|---|---|---|
| 1 | $600.00 | $152.00 | $8,952.00 |
| 2 | $600.00 | $143.04 | $8,495.04 |
| 3 | $600.00 | $133.85 | $8,028.89 |
| 4 | $600.00 | $124.73 | $7,553.62 |
| 5 | $600.00 | $117.05 | $7,070.67 |
| 6 | $600.00 | $109.24 | $6,579.91 |
| 7 | $600.00 | $101.28 | $6,081.19 |
| 8 | $600.00 | $93.19 | $5,574.38 |
| 9 | $600.00 | $84.94 | $5,059.32 |
| 10 | $600.00 | $76.54 | $4,535.86 |
| 11 | $600.00 | $68.00 | $4,003.86 |
| 12 | $600.00 | $59.30 | $3,463.16 |
How the payoff date is worked out
Every month, two things happen to each debt, in this order: interest is added, then your payment is taken off. The calculator repeats that until the balance reaches zero, and the number of times it has to repeat is your payoff date. There is no closed-form shortcut once several debts and a shifting surplus are involved, which is why the answer comes from a month-by-month simulation rather than a single formula.
The interest added to one debt in one month is:
interest = balance × (annual rate ÷ 12)
A $6,000 balance at 22.99% is charged 22.99% ÷ 12 = 1.9158% in a month, which is $114.95. That figure is added to what you owe before any payment is applied, so the payment has to clear the interest before it touches the principal. If you pay $150 against that debt, $114.95 of it services the interest and only $35.05 comes off the balance.
Where the surplus goes
Every debt receives its minimum payment. Whatever is left of your monthly total — the surplus — goes to exactly one target debt. Which debt that is depends on the method:
- Avalanche targets the highest interest rate, because that is where each dollar cancels the most future interest.
- Snowball targets the smallest balance, because that is the debt that disappears soonest.
When a debt clears, its minimum payment is freed. That money is not returned to you — it joins the surplus and goes to the next target. This is the part people underestimate. Each cleared debt permanently increases the amount attacking the remaining ones, so the schedule accelerates rather than running at a constant pace. It is also why both methods finish far sooner than the minimums-only baseline, and often within a month or two of each other.
A worked example you can check
Take three debts totalling $9,400 — a $900 store card at 29.99%, a $6,000 credit card at 22.99%, and a $2,500 personal loan at 6.99% — with minimum payments of $30, $150 and $120, and $600 a month available.
In month one, interest is $22.49 on the store card, $114.95 on the credit card and $14.56 on the loan: $152.00 in total. The minimums come to $300, leaving a $300 surplus. Under avalanche that surplus goes to the store card at 29.99%, which therefore receives $330 against a balance of $900 plus $22.49 of interest.
Repeating that for every month gives:
| Approach | Months | Interest paid |
|---|---|---|
| Avalanche | 19 | $1,427.27 |
| Snowball | 19 | $1,657.92 |
| Minimum payments only | 77 | $6,448.64 |
The result worth noticing is not that avalanche wins. It is the size of the two gaps. Choosing avalanche over snowball saves $230.65. Choosing either one over paying the minimums saves $5,021.37 and finishes 58 months sooner. The decision that moves the number by a factor of twenty is how much you pay, not which order you pay it in.
Where these figures will differ from your statement
This calculator charges interest once a month against the balance you owed at the start of it. Real card issuers charge daily, against an average daily balance, so the exact total depends on which day of the month your payment arrives — something the calculator cannot know and does not ask. Paying earlier in the cycle costs slightly less than this model predicts; paying later costs slightly more.
For scale: the repayment estimate on your own statement is produced under Regulation Z Appendix M1, and that regulation sets its accuracy standard explicitly — a minimum payment repayment estimate shall be considered accurate if it is not more than 2 months above or below
the figure the appendix's own guidance produces. It makes the same simplifying assumptions this calculator does — no new spending, a constant payment, no grace period. So the figure printed by your card issuer is an estimate on the same footing as this one, not a precise quote.
Four things will pull the real number away from the modelled one:
- New spending. The model assumes you add nothing. Every purchase resets the arithmetic.
- Variable rates. The rate you enter is held constant for the whole schedule. Most card rates track a base rate and move.
- Promotional and deferred-interest periods. A 0% balance transfer that expires mid-schedule is not modelled.
- Fees. Annual fees, late fees and balance transfer fees are not included.
How we check the arithmetic
The calculation lives in a pure function with no interface attached to it, and it is tested against a figure that exists outside this site. A $10,000 loan at 6.00% over 60 months has a published monthly payment of $193.33, from the standard loan formula every lender and amortisation table uses. Fed that payment, the engine here clears the balance in exactly 60 months and reports $1,599.68 of interest — matching the closed-form figure to the cent.
Rounding is done the way a statement does it: to the cent, every month, rather than accumulated at full precision and rounded once at the end. The final payment is reduced to exactly what is left rather than taking the full amount, so the schedule never overshoots. The tests are public and you are welcome to read them.
Common questions
- Why does this not match the payoff date on my statement?
- Two reasons, both structural. Card issuers charge interest daily against an average daily balance, so the exact figure depends on which day of the month your payment lands — something no calculator can know. And the repayment estimate printed on your statement is itself an estimate: Regulation Z Appendix M1, which defines how issuers must produce it, states that such an estimate "shall be considered accurate if it is not more than 2 months above or below" the figure its own guidance produces. A difference of a few dollars, or a month either way, is expected.
- Does the avalanche method always cost less than snowball?
- In pure interest, yes — targeting the highest rate first is mathematically optimal, and this calculator will never show snowball costing less. But the size of the gap varies enormously with your figures, and it is often small. On the example above the difference between the two methods is $230, while either one saves $5,021 against paying only the minimums. Run your own numbers rather than assuming the gap is large.
- What happens if my minimum payment is less than the interest?
- The balance grows. The calculator detects this and says so plainly instead of showing an impossible payoff date — the schedule will show the balance rising and the principal column going negative, which is what negative amortisation looks like month by month.
- Is anything I type sent to your server?
- No, and there is no server to send it to. This is a static page; every figure is computed in your browser by JavaScript that has already been downloaded. The shareable link in your address bar carries balances, rates and minimum payments only — never the names you give your debts.
- Can I keep a copy of the schedule?
- Yes, two ways. Download spreadsheet (CSV) gives you every row for your own analysis. Save as PDF or print produces a document containing your debts, the summary figures, the chart and the complete month-by-month schedule, with a link back to the exact scenario so whoever you send it to can change the numbers themselves.
Sources
- CFPB — How is my credit card interest calculated? — retrieved 2026-08-07
- Regulation Z, Appendix M1 — Repayment Disclosures — retrieved 2026-08-07
- The monthly payment cross-check uses the standard loan payment formula, P = B·i ÷ (1 − (1 + i)−n), which is independently derivable and quoted identically by every amortisation table.
Written and maintained by Vikash Singh. Last verified 2026-08-07.