Plan the payoff. Pick the method. Knock out the debt.
Two methods dominate the debt-elimination literature: snowball (smallest balance first, for behavioural momentum) and avalanche (highest APR first, for mathematical optimality). This calculator runs both on the same debt list so you can see exactly what each method costs in dollars and months, and choose the one that you’ll actually stick with.
Debt payoff calculator
Add each debt with its balance, APR, and minimum payment. Set any extra amount you can put toward debt each month. The calculator simulates both methods month by month.
The two methods, in plain numbers
Snowball orders your debts by balance, smallest first, and throws every spare dollar at the smallest until it’s gone. The freed-up minimum payment then rolls into the next debt — the “snowball” that gets bigger as each debt clears. The math is sub-optimal: by ignoring APR, you sometimes pay more interest than you would under the alternative. The behaviour, however, is winning. People stick with snowball longer because the early small wins build momentum, and the literature confirms that completion rates are higher with snowball than with avalanche for households with multiple small debts.
Avalanche orders by APR, highest first. Mathematically, this is the cheaper method — you neutralise your most expensive debt first, where every dollar of avoidance saves the most interest. The trade-off is psychological: avalanche often starts with a large balance that takes months to dent, and households without strong financial discipline can lose motivation before the first win arrives. The dollar saving is real, but only if you finish.
The calculator above runs both on the same debt list. Compare the “total interest” figure between the two; if it’s less than a few hundred dollars different, pick the method you’ll actually finish. If it’s thousands different, the math may be worth the harder behavioural choice. The snowball vs avalanche page works through the trade-off in detail.
What “extra payment” actually does
The extra-payment field is the lever that moves debt-payoff timelines the most. With minimum payments alone, US-issuer revolving credit-card debt at 23 % APR takes 27–35 years to clear if you carry the typical 2 % minimum — and the lifetime interest exceeds the original principal by a multiple. Adding even $50–$100 of extra monthly payment, deliberately routed to the focus debt under either method, compresses that timeline to 4–6 years and saves a substantial fraction of the lifetime interest.
The reason: minimum payments on revolving debt are designed to keep the debt outstanding indefinitely, not to retire it. The minimum is approximately the interest plus a sliver of principal — intentionally calibrated to be the “snail’s pace” of repayment. Any payment above the minimum goes 100 % to principal (under standard US issuer rules following the CARD Act of 2009’s payment-allocation provisions), so the marginal value of each extra dollar is high. The behavioural-finance literature is clear: a small fixed extra payment, automated, dramatically outperforms larger sporadic payments.
The cascade effect — what makes the snowball roll
The mechanical engine of either snowball or avalanche is the cascade: when one debt clears, its minimum payment is added to the focus payment on the next debt. That freed-up amount accumulates as you progress. By the time you reach the last (largest, in snowball; lowest-rate, in avalanche) debt, you may be throwing a payment three to four times the original minimum at it — clearing it in months instead of years.
The cascade is why neither method “just makes minimum payments forever.” It is also why a clean payoff order matters: skipping the cascade by paying randomly across debts wastes the freed-up momentum. Stay disciplined: extra goes to the focus debt only, and freed-up minimums roll forward in order.
When neither method is right
Snowball and avalanche are both forward-payoff methods. They assume you can comfortably make all your minimum payments and have at least some extra to direct. If that is not your situation — if minimum payments alone exceed your income after essential expenses — the calculator will show a non-converging plan, and the right next step is not a payoff method but a debt-relief consultation.
Specifically: contact a credit counselor at an NFCC-member agency (in the United States) for a free initial consultation; they may recommend a Debt Management Plan (DMP) with reduced rates, debt settlement (with disclosure of the credit-score and tax implications), or in extreme cases bankruptcy filing. The negotiation page covers the working contours of each option. Snowball and avalanche presume the debt is already on a sustainable repayment path; if it isn’t, the methods don’t apply.
The credit-score consideration
Paying down credit-card balances aggressively does help your credit score: utilisation (balance / limit) is a major scoring factor, and dropping utilisation from 70 % to under 30 % typically lifts FICO scores by 30–80 points within a billing cycle. Closing the cards once paid off is usually counterproductive — the loss of available credit raises utilisation on remaining accounts and shortens the average account age. Pay down, but keep the accounts open with a small recurring charge that you auto-pay in full.
For installment debt (auto loans, student loans, personal loans), the score effect of accelerated payoff is smaller and more delayed. The score benefit comes mainly from on-time payment history rather than from accelerated payoff. Pay extra to save interest, not primarily to lift the score.
Methodology and editorial standards
The simulation runs monthly: each debt accrues interest at APR/12, then receives its minimum payment, then the “available pool” (extra plus freed-up minimums from cleared debts) is applied entirely to the current focus debt under the selected method. The simulation cap is 600 months (50 years); plans that do not converge within that window are flagged. Calculations follow the standard US revolving-credit and installment-loan conventions described in the AFCPE Accredited Financial Counselor curriculum and the NFCC Counselor Certification Program. Reviewer credentials are verifiable on the AFCPE certificant directory and the Financial Therapy Association FBS™ member roster. Calculation discrepancies are corrected within five business days where reproducible — see the contact page. Editorial corrections are timestamped and an audit trail is retained.