Debt Avalanche Calculator
This calculator compares the Debt Avalanche and Debt Snowball approaches and provides estimated payoff time, total interest, and total amount paid based on your entries. Enter balances, APRs, and minimum monthly payments for up to six debts, and specify any extra monthly amount you will apply above minimums.
The tool uses an aggregated effective-rate approximation to provide fast, comparable estimates for both approaches. It is designed for planning and comparison; it is not a legally binding amortization schedule.
Allocates any extra monthly payment to the debt with the highest APR while paying each account's minimum. Uses an aggregated effective-rate approximation to estimate payoff time and totals. See methodology notes and accuracy caveats in page content.
Inputs
Results
Months to payoff (approx.)
0
Years to payoff (approx.)
0
Total interest paid (approx.)
$0.00
Total amount paid (approx.)
$0.00
Total balance
$0.00
| Output | Value | Unit |
|---|---|---|
| Months to payoff (approx.) | 0 | months |
| Years to payoff (approx.) | 0 | years |
| Total interest paid (approx.) | $0.00 | currency |
| Total amount paid (approx.) | $0.00 | currency |
| Total balance | $0.00 | currency |
Visualization
Methodology
To make multi-account estimates tractable and responsive in a browser environment, the calculator aggregates individual debts into an effective single-loan model by computing a weighted average APR (weights: current balances). It then applies a closed-form amortization approximation to estimate months to payoff given the total monthly payment (sum of minimums plus any extra).
The Avalanche method described here is conceptual: in practice extra payments are applied to the highest-interest account first. The Snowball method applies extra payments to the smallest-balance account first. For transparency and speed we keep the same aggregated numeric estimator for both methods so users can compare estimated outcomes quickly; exact schedules can differ and are discussed in caveats.
Worked examples
Example: Three debts totaling $12,000 with a weighted APR of 14% and a total monthly payment of $600 yields an estimated payoff time of approximately 24 months and estimated interest of about $2,400 using the aggregated approximation.
Example: Same balances and payments under Snowball may produce similar aggregated estimates but can differ in real schedules if small balances are paid early; use the Snowball method in the UI to compare behavioral differences.
Expert Q&A
Are these results exact?
No. Results are approximate. The tool uses a weighted-average approximation and closed-form estimator to produce quick, comparable outcomes. For exact per-account amortization schedules you should use a detailed iterative amortization engine or export data to a spreadsheet and compute per-debt stepwise allocations.
Why use a weighted APR instead of modeling each debt separately?
A weighted APR + closed-form approach gives fast, explainable estimates and lets people quickly compare strategies. Exact modeling requires iterative, account-by-account simulation which is slower and more complex to present in compact UI. We provide guidance and limits so users know when to seek a detailed schedule.
What inputs make the estimator unreliable?
Cases with extremely low total monthly payment (less than monthly interest), promotional 0% APR periods, negative interest, or changing minimum payments over time can make the approximation inaccurate. The calculator clamps values to avoid division-by-zero and reports zero months when payment is nonpositive. See the methodology and accuracy notes.
Is my data stored or shared?
This configuration does not specify storage. Implementations should follow applicable privacy laws and best practices such as least-privilege data handling and encryption in transit and at rest when personal financial data is stored.
Sources & citations
- NIST - Numerical Standards and Guidelines — https://www.nist.gov
- ISO - International Organization for Standardization (numeric accuracy and quality management) — https://www.iso.org
- IEEE - Standards Association — https://www.ieee.org
- OSHA - Organizational safety & process guidance (governance best practices) — https://www.osha.gov