When it comes to figuring out how the interest is calculated in your bill you are going to want to read the rates and charges section of the credit card company that you are through. There is more than one way for a credit card company to calculate your interest.
You may have to pay interest on an average daily balance. When you are paying on the average daily balance you are going, to be paying interest on what you complete balance for each month and averaged out with the amount of days that are in the month. There is times that this method could be an advantage for you if you are not one that charges a lot onto your credit card all the time.
You could have signed to an adjusted balance for your interest fees. With the adjusted balance you are pretty much not paying on the present charges for the billing cycle but you are going to be charge an interest rate for the previous balances that you have carried over.
You may be getting charged interest on a system called previous balance finances. With the previous balance, you are able to avoid any finance charges for any present charges if you pay on the balance before the end of there billing cycle. That is going to be a good advantage because if you are being paid in the middle of the billing cycle you will be able to pay the balance down as much as possible so you can avoid the high interest fees at the end of the month.
The only other way that credit card companies charge interest on the accounts is with the two-cycle balances. This is where the credit card company will charge you interest twice in the billing cycle so that you will end up paying more in the end if you are not careful on how they are charging you.
No matter what the credit cards method of calculating your interest you can always call the credit card company and ask for a description of how they are calculating the interest on your account, if you cannot figure it out your self, they are there to help you out with your questions. There is plenty of times that they credit card companies are even going to put the calculations on your bill each month so that you could have a little easier time figuring it out on your own.