If my current credit card balance in July is \$1,000 USD, my credit card's APY is 20% and this month I made a payment for \$100 on time (to avoid late fees)... What will my balance be in August?
I don't think it will be \$900 or \$900 + 20%. It should be $900 + some amount I don't know how to calculate.
I kind of remember this involving compound interest and/or logarithms, but I honestly don't remember most of my math classes beyond pre-cal. Could someone point me in the right direction?