The math-optimal payoff strategy.

The debt avalanche strategy pays off the debt with the highest interest rate first. This minimises total interest paid - saving real money over the life of the payoff. This calculator estimates your time to zero with avalanche, total interest paid, and total paid.

For 15,000 in debt at a highest blended rate of 20% with 500 monthly payments, avalanche takes about 39 months and costs 19,425 total - 4,425 in interest. Reducing the payment to 400 stretches it to 52 months and raises interest to 5,845. Every extra 100 a month knocks years off the timeline.

The calculation treats your total debt as a single balance at the highest rate, which slightly overstates interest. Real-world avalanche payoff bunches highest-rate debt first then moves to lower rates - typically 10-20% less interest than this single-rate estimate. Use the tool as an upper-bound estimate.

Run it with sensible defaults

Using total debt balance of 15,000, highest interest rate of 20%, total monthly payment of 500, the calculation works out to 42 months. Nudge the inputs toward your own situation and the output recalculates instantly. The defaults are meant as a starting point, not a recommendation.

The levers in this calculation

The inputs — Total Debt Balance, Highest Interest Rate, and Total Monthly Payment — do not pull with equal force. Not every input has equal weight. Flip one at a time toward extreme values to feel which ones move the needle most for your situation.

How the math works

Standard amortisation formula with total balance and highest rate. Months = -ln(1 - (B × r)/P) / ln(1 + r). Overstates interest by assuming all debt at highest rate. The working is transparent — you can verify every step yourself in the formula section below. No black box, no opaque "proprietary model".

Reading the output honestly

The payoff date assumes every payment lands on time and at the amount you entered. In reality, months with unexpected expenses happen. Treat the figure as the best-case timeline and add a buffer for life if you want a realistic target.

What this doesn't capture

Real payoff journeys include missed payments, fee changes, balance transfers, and promotional rates that reset. The calculation assumes a steady plan; reality is rarely that clean. Use the figure as the best-case plan against which actual progress gets measured.