Yeah, Safari is right.
I was thinking about transaction fees (like transferring a balance over).
"Finance charges" and "interest charges" we're both being used interchangably in the OP's question. That's why I was getting confused
If you don't pay the balance in full each and every month, you will be subject to extra charges. Call them whatever you like. And companies do work out the amounts differently.... but if you don't think it's correct, you can call them and ask for an explanation.
Also as far as I know, if you pay directly to the credit card company website; that's the only way to get it credited the same day.
But I don't think most people go to each CC website to pay their bills directly... I think (and I could be wrong here too) many people use their bank's online bill pay.
I do use the online bill pay and my bank says to "allow" for 3 or 4 business days for processing... they usually don't take that long either... except for the one payment.
Stamping an envelope and sending checks, is the slowest method of payment....
I don't know which method the OP uses, but that may impact fees if the payment does not get processed in their time limit.