How credit card payoff is calculated
At each month-end, add balance × APR ÷ 12, subtract the payment, and repeat. Trim the final payment to the remaining balance and interest. Payments that do not reduce principal are rejected.
Worked example
A $1,000 balance at 0% APR with $300 monthly payments clears in four months: $300, $300, $300 and $100. There is no interest in this example.