Debt spreadsheet methodology and limits

The downloads are original editable workbooks. Their examples use invented USD amounts, and the methods below define what their results mean.

Shared conventions

Money inputs are non-negative amounts. Interest and monthly payment results are rounded to cents. A required blank is different from an intentional zero: affected outputs become n.a. rather than dropping the missing amount from a total. Percentages are stored as numeric fractions in Excel and entered as percentages in the browser form. Dates are real date values; monthly payment dates advance from the first entered date, capping the day at month-end where necessary.

Multi-account calculation order

Each month opens with the previous closing balances. Interest equals opening times APR/12, rounded to cents. The minimum is the lower of total owed and MAX(fixed floor, opening times minimum share plus interest). The sum of minimums is compared with the month’s available budget before any payment is allocated. A shortfall stops the future projection.

After minimums, the extra pool is allocated to the smallest opening balance for snowball or highest annual rate for avalanche. Equal priority values retain account row order. Each account can receive at most its remaining amount owed; unused extra passes to the next account during the same month. A zero-balance account consumes no payment. A fixed overall budget therefore carries released payment capacity forward automatically.

The Excel model evaluates up to 360 months, including zero-balance rows after payoff. The browser schedule stops once debt reaches zero or at the first budget shortfall. Both use the same stated conventions for completed months. A remaining balance after 360 months is not reported as a payoff. The browser CSV contains completed account rows and a status header; it is a projection, not proof of actual payments. Exported scenario JSON stores editable assumptions, not a bank statement.

Actual balance tracker

Five balances are required for a monthly total. Progress compares that total with the opening total. A zero opening total has no defined percentage reduction. Future missing observations remain unavailable. A decrease in balances does not equal payments or interest saved.

Single-loan schedule

The regular payment uses the level-payment annuity formula, with principal divided by term at zero interest. Interest is calculated monthly on opening principal. The entered extra is applied after the regular amount. Payments cap at amount owed, and the contractual final month pays any residual caused by cent rounding. There are no fees, insurance, daily interest or new draws.

Verification and application support

Checks cover numerical conservation, changing minimums, ordering ties, a zero rate, all-zero debts, insufficient budgets, monthly overrides, blank versus zero and a horizon without payoff. Workbook worksheets are rendered and inspected. Microsoft Excel recalculation, input changes and save/reopen are tested in separate disposable files. Native Google Sheets verification is not claimed.

What the examples cannot establish

The models do not establish creditor minimums, legal priority, settlement eligibility, a credit score, collection rights or affordability. Real cards may have daily balances, multiple APR categories, grace periods and fees. Entered budgets must reflect real available money; this planner does not model household expenses or borrow to cover a shortfall. Confirm account-specific terms before using a result to schedule a payment.

Sources and calculation basis

The CFPB description of debt reduction strategies explains paying minimums across debts and directing extra money to a selected priority. Its explanation of credit-card interest describes why real statements may use daily balances and different rates. These sources support the concepts. All workbook layouts, monthly model conventions and invented USD examples here are AllMarkets material.