Calcs.finance

Formula and help

Debt Payoff Calculator Formula and Help

Learn how this calculator works, what formula it uses, and which assumptions sit behind the estimate.

Educational estimate, not financial advice.

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How it works

The Debt Payoff Calculator estimates a generic debt-avalanche schedule for up to 10 entered debts. It keeps each debt's type label, balance, scheduled monthly payment, annual rate, extra monthly amount, yearly extra amount, one-time payment, fixed-total-payment setting, payoff time, total paid, total interest, first payoff, final payoff, and avalanche order visible so the calculation can be checked.

Use this calculator when you want to compare how entered balances, rates, scheduled payments, and extra-payment timing affect a multi-debt payoff estimate. Use Fixed Payment Credit Card Payoff for one card with one fixed payment, Credit Card Payment Plan for fixed, minimum-percent, or target-time card modes, DTI when recurring payments need to be compared with income, Budget when the whole monthly cash-flow picture matters, Payment or Loan Payment for installment-loan math, APR when fees and legal disclosure rates matter, and CFPB, FTC, lender, servicer, tax, credit-reporting, legal, debt-counseling, or local regulatory sources for account-specific debt-relief, collection, settlement, hardship, payment-allocation, bankruptcy, tax, legal, regulated-advice, or jurisdiction-specific questions.

Formula notes

This formula page covers the app's Debt Payoff Calculator: a generic month-by-month debt-avalanche simulator for up to 10 entered debts. It keeps only rows with a positive starting balance, adds simplified monthly interest, applies each debt's scheduled payment, then sends any remaining budget to the highest-rate active debt with a smaller-balance tie-breaker. It does not calculate creditor minimum-payment rules, issuer payment allocation, fees, promotional APRs, collection outcomes, settlement, counseling plans, bankruptcy, tax treatment, credit reporting, legal outcomes, or personalised debt advice.

Active = debts where B_i0 > 0; r_i = APR_i / 100 / 12; Order = sort(rate desc, starting balance asc); S_fixed = sum(Pay_i0); Budget_t = (fixedTotal ? S_fixed : sum(Pay_i for active debts)) + Extra_m + (t mod 12 == 0 ? Extra_y : 0) + OneTime_t; B_i' = B_i + B_i * r_i; B_i'' = B_i' - min(Pay_i, B_i'); ExtraBudget then pays highest-rate active debts until zero; stop when all B_i <= 0 or t = 1200

Each simulated month adds interest first, applies each active debt's scheduled payment, then routes the remaining payment budget through the avalanche order until balances are paid off or the safety cap is reached.
SymbolMeaningHow this page uses it
B_i0Starting balance for debt iThe balance entered for a debt row. Rows with a balance of 0 or less are ignored by the simulation.
APR_iEntered annual rate for debt iThe annual percentage rate entered for that debt row. It is treated as a simplified annual rate, not as a real statement or contract rate method.
r_iSimplified monthly rateAPR_i divided by 100 and then by 12.
Pay_iScheduled payment for debt iThe entered monthly payment for that debt row. The model applies this scheduled amount before extra-payment targeting.
S_fixedOriginal scheduled-payment totalThe sum of scheduled payments across active debts at the start of the simulation.
Budget_tPayment budget in month tScheduled-payment budget plus monthly extra, yearly extra when month t is divisible by 12, and the one-time extra only in its selected month.
OrderAvalanche orderActive debts sorted by highest entered annual rate first, with smaller starting balance used as the tie-breaker.
I_i,tInterest for debt i in month tThe current remaining balance times r_i, added before payments for that month.
NPayoff monthsThe number of simulated months until all active balances are paid off, subject to the 1200-month safety cap.
TotalPaidTotal paidThe sum of scheduled and extra payments actually applied during the simulation.
TotalInterestTotal interestThe sum of monthly interest added across all active debts.

Step by step

  1. Read up to 10 debt rows from the calculator inputs: name, balance, scheduled monthly payment, and entered annual rate.
  2. Filter out rows whose starting balance is 0 or less. The remaining rows become the active debt set.
  3. Calculate starting debt as the sum of active starting balances, and calculate the original scheduled-payment total from the active scheduled payments.
  4. Build the avalanche order by sorting active debts by entered annual rate descending. If rates tie, use the smaller starting balance first.
  5. Start a monthly loop and stop when every active balance is paid off or when the implementation reaches the 1200-month safety cap.
  6. For each active debt in a month, convert the entered annual rate to a simplified monthly rate with APR / 100 / 12 and add balance times that rate as interest.
  7. Calculate scheduled-payment budget. If Fixed total monthly payment is Yes, keep the original scheduled-payment total available after debts are paid off. If it is No, use only the scheduled payments for debts still active that month.
  8. Add Extra payment per month every month, add Extra payment per year only on months divisible by 12, and add the One-time extra payment only in the selected One-time payment month.
  9. Apply each active debt's scheduled payment first, capped at the remaining balance after interest. This scheduled pass can pay a debt off before the extra-payment pass starts.
  10. After scheduled payments, send any remaining budget to the current highest-rate active debt. If that debt is paid off and budget remains, repeat the sort and target the next highest-rate active debt.
  11. Record the first debt paid off, its payoff month, the final debt paid off, total paid, total interest, payoff months, formatted payoff time, and avalanche order.
  12. Round displayed currency outputs to two decimals after the full-precision monthly simulation.
  13. Use CFPB, FTC, Regulation Z, lender or servicer agreements, credit-card agreements, tax, bankruptcy, credit-reporting, legal, debt-counseling, or local regulator sources before turning this calculator math into real collector, settlement, issuer-allocation, fee, hardship, default, lawsuit, garnishment, forgiven-debt tax, credit-reporting, legal, regulated-advice, or jurisdiction-specific guidance.

Sources and validation

This calculator is an original implementation based on the app's documented multi-debt avalanche simulation, fixed planning assumptions, deterministic fixtures, edge cases, rounding policy tests, and internal validation. It is not copied from a single source.

Outputs are checked with deterministic fixtures, edge cases, rounding policy tests, and internal validation artifacts. The result remains an educational estimate, not a creditor payoff quote, issuer payment-allocation rule, debt-management plan, settlement strategy, counseling recommendation, bankruptcy answer, tax answer, legal answer, credit-reporting forecast, regulated debt advice, or personalised advice.

  • CFPB debt collection resources should be used before copy discusses collectors, debt validation, consumer rights, complaints, collection communications, lawsuits, garnishment, or collection-account context.
  • CFPB credit-counseling, debt-settlement, debt-consolidation, and credit-repair guidance plus FTC debt guidance should be used before copy discusses debt-management plans, settlement risks, consolidation costs, credit repair, debt-relief providers, upfront fees, scams, or repayment proposals to collectors.
  • CFPB credit-card interest guidance and Regulation Z section 1026.53 should be used before copy discusses real card APR buckets, excess-payment allocation, deferred-interest balances, promotional balances, issuer allocation rules, or card-specific payoff behavior.
  • Lender and servicer agreements, credit-card agreements, tax authorities, bankruptcy materials, credit-reporting sources, legal sources, debt-counseling providers, and local regulators should be used before copy makes product-specific, fee, hardship-plan, default, lawsuit, garnishment, forgiven-debt tax, credit-reporting, legal, regulated-advice, or jurisdiction-specific claims.

See the Calcs.finance methodology for the full review approach.

Assumptions

  • Debt rows are planning rows, not creditor records. The type label helps organize the estimate, but the calculator does not load real balances, statements, due dates, minimum-payment formulas, credit-card APR buckets, promotional terms, hardship plans, servicer rules, or collection status.
  • Scheduled payments are applied to each active debt before the extra-payment budget is aimed at the highest-rate active debt. The model assumes the entered scheduled payments are allowed and made on time, and it excludes late fees, returned-payment fees, over-limit fees, prepayment penalties, new borrowing, new card spending, settlement offers, consolidation-loan costs, credit-counseling plan fees, tax effects, credit-reporting changes, lawsuits, garnishment, bankruptcy, and legal outcomes.
  • Scoped independent comparator checks pass for overlapping multi-debt avalanche fixtures, with named evidence kept in internal validation files only. CFPB debt collection, debt-negotiation, credit-counseling, and credit-card interest materials, FTC debt guidance, Regulation Z payment-allocation rules, lender or servicer agreements, tax authorities, legal sources, credit-reporting sources, debt-counseling providers, and local regulators are needed before making real collection, settlement, payment-allocation, fee, hardship, default, forgiven-debt tax, credit-reporting, legal, regulated-advice, or jurisdiction-specific claims. Results are educational estimates, not financial, tax, legal, lending, credit, debt-counseling, regulatory, or personalised advice.

Formula version 2026.05.22-generic-debt-avalanche

Common mistakes to avoid

  • Entering only extra payments and leaving scheduled payments at zero. The app applies each debt's scheduled payment first, so missing scheduled payments can make the payoff estimate much slower or less realistic.
  • Reading fixed total monthly payment as a creditor rule. Yes means the model keeps the original total payment budget after a debt is paid off; No lets the modeled monthly payment decline as debts drop out. It is not an automatic creditor transfer between accounts.
  • Treating the avalanche order as account-specific advice. The app sorts by entered annual rates and starting balances; it does not evaluate minimum-payment rules, legal risk, collections, settlement offers, credit-reporting consequences, cash-flow hardship, taxes, or whether a different repayment method fits a personal situation.

Worked example

Default and no-rollover examples

These examples use the package fixtures so the formula page matches the production calculator rather than a generic payoff worksheet.

  1. The default fixture starts with four active debts: an $8,000 credit card at 21.99 percent, a $12,000 personal loan at 11.5 percent, an $18,000 auto loan at 7.25 percent, and a $15,000 student loan at 5.5 percent.
  2. Starting debt is $53,000.00 and original scheduled payments total $1,155.00 per month.
  3. The avalanche order is Credit card > Personal loan > Auto loan > Student loan because the entered rates descend in that order.
  4. With fixed total monthly payment set to Yes, $300 extra each month, $1,000 extra each year, and a $2,500 one-time payment in month 6, the model keeps the original scheduled-payment budget rolling as debts are paid off.
  5. That fixed-total fixture pays the credit card first in month 12, pays the student loan last, and reports 38 payoff months, or 3 years and 2 months.
  6. Total paid is $59,978.88 and total interest is $6,978.88 after rounding.
  7. In the no-rollover fixture, the same four debts have no extra payments and Fixed total monthly payment is No, so scheduled payments decline as debts are paid off.
  8. That no-rollover fixture reports 104 payoff months, or 8 years and 8 months, with $67,070.42 total paid and $14,070.42 total interest.
  9. The difference shows the model's rollover and extra-payment assumptions. It is not a creditor payoff quote, payment instruction, settlement plan, counseling recommendation, legal answer, tax answer, or credit-reporting forecast.

The formula page explains how the app simulates entered debts. Real accounts can differ because creditor minimums, payment allocation, fees, daily interest, promotional balances, hardship terms, collections, settlements, taxes, legal status, and credit reporting are outside this calculator.

What this formula does not include

  • The app uses each debt's entered annual rate divided by 100 and 12 as a simplified monthly rate. Real accounts can use daily interest, average daily balance methods, multiple APR buckets, or contract-specific accrual rules.
  • The calculator does not know whether an entered scheduled payment satisfies a real creditor's minimum-payment rule, hardship plan, debt-management plan, court order, settlement agreement, or servicer instruction.
  • Payment allocation is simplified. The app allocates scheduled payments by row and extra budget by entered annual rate; it does not reproduce issuer allocation rules for multiple credit-card balances, secured balances, deferred-interest balances, or promotional APRs.
  • No new borrowing, new card spending, late fee, returned-payment fee, over-limit fee, balance-transfer fee, cash-advance fee, penalty APR, prepayment penalty, or collection cost is modeled.
  • Fixed total monthly payment means the model keeps the original scheduled-payment total available after a debt is paid off. It is not an automatic transfer between creditors or proof that a real payment plan allows rollover.
  • If the entered payments are too low to amortize under the simple monthly-rate model, the simulation can reach the 1200-month safety cap. The current output does not separately label cap-limited schedules.
  • The calculator does not evaluate debt settlement, debt consolidation, credit counseling, hardship plans, bankruptcy, tax treatment of forgiven debt, legal defenses, garnishment, lawsuits, credit reporting, credit scores, or regulated debt advice.
  • Results are educational estimates from entered assumptions, not financial, tax, legal, lending, credit, debt-counseling, regulatory, product-specific, jurisdiction-specific, or personalised advice.

Terms used in this calculator

Avalanche order
The active debts sorted by highest entered annual rate first. When rates tie, the app uses the smaller starting balance first as its tie-breaker.
Fixed total monthly payment
A setting that keeps the original total scheduled-payment budget available after a debt is paid off. It models payment rollover, but it is not an automatic creditor transfer or a debt-management-plan rule.
Extra payment budget
Monthly, yearly, and one-time extra amounts added to the scheduled-payment budget. After scheduled payments are applied, the remaining budget targets the highest-rate active debt.

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