The snowball strategy pays off debts from the smallest balance to the largest while keeping minimum payments on all debts.

Monthly interest: $$Interest = Balance \times \left( \frac{APR}{100 \times 12} \right)$$

Balance update: $$New\ Balance = Old\ Balance + Interest - Payment$$

Each month, minimum payments are applied across all debts, then all extra cash goes to the smallest remaining balance. Once a debt is closed, its minimum payment is rolled into the next debt, accelerating payoff momentum.