Credit card minimum monthly payment

Credit cards do are not generally linked to a bank account. You may be thinking of a debit account, in which your purchases are paid for directly from a bank account.

Credit cards don't require you to pay your balance in full every month. In fact, they would actually prefer that you don't -- they make most of their revenue from interest payments. However, they do want to encourage you to pay eventually; if you just keep charging without ever paying, they lose money (you'll also have a lousy credit score, so there are other disincentives for you to do this, but that's outside their control).

If you don't pay your balance in full by the due date, future bills will incur interest fees for the unpaid balance.

But if you pay less than the minimum payment, you will get charged an additional late fee (which can be much larger than the interest) and there can be other penalties, such as interest on future purchases starting on the purchase date rather than on the due date of the bill.

So you can avoid all fees by paying your bill in full each month, and avoid extra penalties by paying at least the minimum required payment.

If you keep paying your full balance, you'll likely find them increasing your credit limit periodically. They're hoping that this will entice you to charge more and overextend yourself, so you'll have to pay interest. Try not to fall for this trick!

(I know this answer is correct for the UK, I am 99% sure it is also correct for the USA, in other parts of the world YMMV).

In my naive understanding of how credit cards work I would expect my actual bank account to be charged the how much I spent in the billing period.

Normally, by default your bank account is not automatically charged anything. It is up to you to pay at least the minimum payment on your bill by the due date. If you don't then penalties will accrue and your credit rating will get dinged*.

With many cards it is possible to set up automatic payments, but this is an optional feature and the choice of whether to have automatic payments and if-so how much is automatically paid is a separate decision from applying for the card in the first place. Typically the card issuer will offer a choice of automatically paying either the minimum payment, a fixed user-specified amount or the full balance.

Minimum payment rules are set up so that if you pay the minimum, you will pay your balance off very slowly and pay lots of interest to the credit card company. They do want you to pay off the bulk of your balance eventually but they have little incentive for you to do it quickly.

What makes minimum payments particularly insidious is that the payment is defined in terms of your current balance, not what you initially borrowed. So each month your minimum payment drops. With the rules you have posted (and assuming you have a balance large enough that the $15 rule doesn't kick in) if you make the minimum payment each month it will take nearly 6 years for your outstanding balance to drop to half it's original value.

Eventually if you keep making the minimum payment and don't charge any new purchases, your balance will drop low enough that the $15 floor on the minimum payment kicks in and some time after that you will eventually pay off the loan, but it can easily take decades to reach that point.

* Eventually of course if you don't pay they will resort to more forceful means to collect the debt, obviously court action is one way, here in the UK if your bank and credit card company are the same they also have the option of "setting off" your debt with them against your credit balance with them. Such mechanisms are beyond the scope of this answer which assumes you will honour your agreement and pay at least the minimum payment on time.