I've just written a blog post that explains the way credit card companies calculate interest charges. Some main points of the post are:
- Some people think that interest only accumulates from the end of a billing cycle, while in reality interest starts accumulating as soon as you make a purchase or take a cash advance.
- The interest is assessed not on the balance of the billing cycle, but on the average balance during the cycle.
- Grace period doesn’t apply if you carry a balance.
- Grace period doesn't apply to cash advance
I also provide numerical examples in the article to illustrate the calculation. If you have any questions about credit card interest or any feedback on the article please let me know. I realize the examples may look confusing to some people. Is there a better way for me to present my points?
http://hiepsfinance.com/2013/06/02/why-is-your-credit-card-bill-so-huge-how-credit-card-interest-is-...
Thanks! 
