Here are three of the ways used by financial institutions to calculate finance charges:

    Adjusted balance - This system, which consumer experts say favors the cardholder, takes the balance from your previous statement, adds new charges, subtracts the payment you made and then multiplies this number by the monthly interest rate.

Regarding your link, MY credit cards works on a variation of the 2nd type with daily compound interest. You seem to have read a lot, mind elaborating exactly what you want to know instead of c&p?

http://en.wikipedia.org/wiki/Credit_card#Interest_charges

@saksoba

Whatever calculations that you use, you still pay interest to the bank and it is just a matter of some interest or a lot of interest. We have seen a lot of readers rant about bank's high interest rate whereas in actual fact they choose to build debt on their credit card thus they should be ready to bear the consequences.

We have said this repeatedly, banks are not charity and they are a commercial entity which wants to make money, pay rental for their branches, pay bills, pay salary to their workers, etc.

To make life simpler, that's the very reason that we do not encourage anyone to build debts on credit cards. You should treat credit card like cash which is to pay in full every month. No need to confuse yourself, just don't ever build debt using your credit card. If you are and that's a sign that you are living beyond your means already.

Cannot afford to buy something then don't buy and don't act as if you can afford it just because you are holding a credit card.
I personally am not too enthusiastic and don't agree about teaching someone about the interest rate calculations as it's like slowly driving you to your own debt grave. If you want to build debt like this then by all means do so and take your own pain to understand the calculation ... cannot understand then take it as a sign not to build debt like that.