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Excel examples use English function names, comma separators and percentages entered with the % sign. Regional settings may require semicolons. Every input is hypothetical. Display two decimal places, but do not round intermediate calculations.
1. Fix the budget
For the default debts, balances are $5,000/$10,000/$2,000, rates 20%/10%/0%, minimums $150/$200/$100 and extra $200. Total monthly budget is $650. Ignore minimums on rows with zero initial balance; add any available cash in the extra field. Keep the initial active-debt budget constant even after accounts are cleared.
2. Build an Excel row
For a single debt enter B2=5000 (opening balance), C2=20% (annual rate), D2=150 (minimum), E2=200 (extra allocated after the other minimums).
F2: =B2*C2/12
G2: =MIN(B2+F2,D2)
H2: =MIN(MAX(0,B2+F2-G2),E2)
I2: =MAX(0,B2+F2-G2-H2)
B3: =I2F2 is $83.333333 interest, G2 $150, H2 $200 and I2 $4,733.333333. Format as currency but retain unrounded balances for the next row.
3. Extend to three debts
Create one block per debt. Each month calculate interest and minimum payments for all three first. The available pool is $650 minus the sum of actual minimum payments. Sort remaining debts by rate descending for avalanche or remaining balance ascending for snowball; break ties by the original debt number. Allocate MIN(pool, balance after minimum) to the first, subtract that allocation from the pool, and repeat for the next. Re-sort snowball each month after interest and minimums.
4. Stop and compare
Copy the row forward until every closing balance is at most half a cent. Sum all interest columns; count months through the final payment. Repeat on a second sheet with the other priority. Use the same $650 budget. Stop at 1,200 rows if debt remains and report that the horizon was exceeded; accumulated interest at that point is not a completed payoff estimate. The simulator uses the same half-cent stopping tolerance.
5. Verify with a small case
At zero interest, a single $1,000 debt paid at $100 a month takes ten months and has no interest. A $250 debt paid at $100 takes three months with a $50 final payment. Changing priority must not create extra payment money.
Match the assumptions
Three debts; enter zero balance for unused rows. Rows with zero opening balance contribute no minimum payment to the budget. Enter any additional cash in the extra-payment field. Interest is charged monthly at annual rate ÷ 12 before payments. Fixed dollar minimums and the full original monthly budget continue after a debt is cleared. Unused minimum payments roll into the selected priority. Ties use row order; snowball orders balances after interest and minimum payments. No fees, new borrowing, promotional-rate expiry, daily interest or changing minimums. Final payments are capped at the amount owed. Unpaid debt after 1,200 months is reported as not repaid.
References and verification
Official references checked for this release on 1 November 2026. Rules and product terms can change.