Compare debt snowball vs avalanche payoff strategies with payment schedules, interest savings, and payoff timeline charts.
Two repayment orders can turn the same monthly debt budget into different interest costs and payoff dates. Using each debt's balance, annual percentage rate (APR), and required payment, the calculator builds monthly schedules for snowball, which targets the smallest balance, and avalanche, which targets the highest APR. It then compares interest totals and payoff timelines. The common input mistake is confusing extra money with the full monthly payment budget, so confirm what the payment field represents.
A concrete input and expected output from the current implementation.
Input
One debt: balance = $1,000; APR = 0%; minimum monthly payment = $100; additional monthly payment = $0
Expected output
Snowball and avalanche both show 10 monthly payments of $100, a 10-month payoff period, $0 total interest, and no interest savings between the strategies.
With only one debt, both strategies must target the same balance. At 0% APR, ten $100 payments repay exactly $1,000 without interest.
The snowball schedule makes each required payment and directs available extra money to the lowest balance. The avalanche schedule uses the same payment pool but targets the highest APR. When a target is cleared, its former payment joins the amount available for the next target, so the targeted payment can grow as debts disappear.
The two projections use the same entered debts and payment assumptions. Each schedule shows how balances decline and when individual debts are cleared. Summary figures and timeline charts compare payoff duration and interest paid. A quick first payoff does not necessarily identify the strategy with the lowest total interest, so compare the complete schedules.
That is expected with one debt because there is no ordering decision. It can also happen when both methods select the same debt at every payoff step, causing them to follow the same sequence. Rounded payoff months may match even when detailed interest totals differ, so inspect both the summaries and monthly schedules.
With fixed APRs, unchanged required payments, and the same total payment amount, targeting the highest-rate balance generally produces the lower modeled interest cost. The answer is no when changing rates, promotional expirations, fees, or other omitted contract terms alter the effective cost. Avalanche can also tie snowball when both use the same payoff order.
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