calculating credit card interest Ok, here's the dizzle. I want to make a spreadsheet that I can use to track credit card balance, interest rates, payments and so on. So, what's the formula for figuring interest on a credit card balance. I'll even give you some hypotheticals to show me with. Assume a balance of card x at $1000. Assume the APR is 18%. What's the formula for calculating how much interest will get tagged on to that $1000 balance at the end of the month. I'm getting close to understanding it better but I just haven't figured it out the rest of the way. And there is no way on earth I am going to try and do this on the phone with a customer screwup representative. So, credit card with a $1000 balance and an 18% APR. I know it's not as simple as taking 18% of the balance each month and tagging that on to the balance. You'd be racking up insane charges for which you'd be making ungodly payments just to keep up with the finance charges. So, someone smrater than me help me out.