Several cards behave differently from one card
A single card has one answer: at this rate, under this minimum payment rule, the balance takes this long. Put three cards side by side and a second question appears that the single-card answer cannot reach. Every card is taking a minimum payment out of the same monthly budget, and each minimum is a share of a balance that is falling. The money you have available therefore changes shape month by month even if you never change what you pay.
This is what makes the minimum-payment trap worse across several cards than on any one of them. Pay each minimum separately and your total outlay drops every month, which feels like progress and is the opposite. Hold the total level and the same money clears the cards years sooner, because the payment freed by each cleared card lands on the next one.
The minimum payment rule matters more than the rate
The rule this page applies to every card is the field that decides the answer, and it is the field nobody explains. A rule that charges a share of the balance plus that month's interest always reduces the balance, because the interest is covered separately. A rule that charges a share of the balance and nothing else has to pay the interest out of that same share, so it only makes progress when the percentage is larger than the monthly rate.
On a card charging a rate in the low twenties a year, the monthly interest is a little under two per cent. A two per cent rule with interest included therefore moves the balance by a couple of tenths of a per cent a month, which is not a payoff schedule but a very slow leak. What rescues it is the floor, the absolute minimum below which the percentage stops applying, and on a large balance the floor is nowhere near.
One rule is applied to every card here rather than one per card. That is a limit of the form rather than a claim about reality: issuers do differ. No public dataset carries any issuer's minimum payment formula, so there would be nothing to fill six separate rules in from, and yours is in your cardholder agreement.
Where the starting rate comes from
The rate on every row starts at the average rate charged on United States card accounts that are actually paying interest, as published by the central bank. It is a market average and it belongs to nobody in particular, which is exactly why it is the starting figure: a page that opened on one issuer's rate would be making a suggestion it has no business making.
It is also not your rate. The line under the rate fields says which period the average describes, and the moment you type over it the page stops claiming the publisher stands behind the number. Your own rate is on your statement, and entering it is the single change that makes this page's answer yours rather than the market's.