How the minimum payment is calculated
Most US issuers charge the greater of a percentage of the balance plus interest, or a floor amount such as $25. This calculator uses 1% of the balance plus accrued interest, with a $25 floor — the most common formula in card agreements.
Because the minimum is recalculated every month on a shrinking balance, the payment declines over time and the payoff date stretches out. That is the trap the fixed-payment comparison exposes.