Calculator Methodology and Assumptions

By PayOffMyBills · Updated September 19, 2026 · Educational information, not personal financial advice.

Our calculators illustrate what follows from the numbers and assumptions you enter. They do not verify account statements or predict creditor decisions.

Multi-debt snowball and avalanche calculators

The September 19, 2026 versions of the snowball and avalanche calculators use the same engine and payment budget. Only the extra-payment priority changes.

1. Convert each balance, minimum and extra payment to integer cents, rounding to the nearest cent. The monthly budget equals all starting minimums plus the extra payment.
2. Set priority once from the starting inputs. Snowball orders smaller balances first, breaking ties by higher APR. Avalanche orders higher APRs first, breaking ties by smaller balance. Remaining ties follow entry order.
3. For each month, calculate interest on each opening balance as balance × APR ÷ 1200 and round to the nearest cent. Add that interest to the account balance.
4. Pay each active account its entered minimum, capped at the amount owed including that month’s interest.
5. Allocate the remaining monthly budget to the first unpaid priority account. If it is paid off, apply any remainder to the next account within the same month.
6. Record account payments, interest and closing balances. Repeat until all debts are paid or the 600-month limit is reached.

Fixed minimums and rollover

The tool does not recalculate percentage-based credit-card minimums. Entered minimums stay constant until payoff. Freed minimum payments remain in the fixed total budget, so entering zero extra still rolls freed payments forward. The final total payment is capped at what remains owed.

Limits and incomplete results

Inputs support 1–20 debts, balances and payments up to $10 million each, and APRs from 0% to 100%. Each balance and minimum must be positive. A plan that still has debt after 600 months is labeled incomplete; interest and payments shown then cover only the modeled period. A numerical guard also stops balances that grow beyond $10 billion in aggregate. Neither case receives a debt-free date.

What the model leaves out

Actual creditors may use daily interest, different payment dates, changing minimums or specific allocation rules. The model excludes fees, new charges, changing APRs, promotional/deferred interest, settlement, forgiveness, tax effects, prepayment restrictions and legal consequences. It cannot predict credit scores. Different rate categories on the same account should not be treated as separate debts unless payments can really be directed independently.

Verification example

A $1,000 debt at 12% APR with a $600 monthly payment incurs $10 in month-one interest, leaving $410 after payment. Month two adds $4.10 interest and requires a final $414.10 payment. Total interest is $14.10. The multi-debt engine is also checked for zero APR, payment rollover, invalid values, incomplete payoff and agreement between principal, interest and total payments.

Privacy of the new comparison tool

Debt inputs and results are calculated in browser memory. The tool has no server submission and does not store those entries after reload. CSV schedules are generated locally. Its entire input and result region is masked from optional session replay. Existing site analytics and consent choices remain separate; calculator usage events do not include entered debt amounts, rates or labels.

Other site calculators

Other tools have their own fields and simplifying assumptions; the multi-debt schedule described above applies specifically to these two updated calculators. A basic single-debt payoff model generally estimates monthly interest from APR, subtracts a fixed payment and repeats. Budget and ratio tools use the amounts entered. Read the assumptions on the tool you are using.

Using an estimate responsibly

Compare the result with the next statement and update inputs when terms change. Ask the creditor for a final payoff quote. If required payments do not fit your budget, use the estimate to identify the gap rather than assuming a strategy order solves it.