I find it interesting how this show up the day after I had to call the customer service to clarify an interest fee on my account that din't make sense. So here is what happened, I got hit with a $12.xx monthly interest on a $2000ish purchase which I made less than 30 days ago and hasn't shown up on my previous statement. For clarification, my current APR on the card is 5.99%.
It took me two reps and two accounts managers to learn how these things are calculated:
1) Interests are daily compounded.
2) Interests are not calculated on actual balance but on the average daily balance.
3) If you don't pay your statement balance in full by the end of the month, you lose your grace period for future purchases and interest would start accruing as soon as the transactions goes through. To reset this it would require you to make two full statement payments in a row.
4) If you purchase something and return it and the return takes a few days to process, you would still pay interest on for those days.
The rep and the first account manager that spoke to weirdly dint have the basic understanding of interest rates. She argued that the $12 interest was on the $2000 for 4 days at the rate of 5.99%. Funny enough, she still din't find anything odd when I pointed out that it would mean, by the end of the year, I would pay $1095 ie. > 50% of the principal in interest!
Anyways the second rep was knowledgeable enough to explain it.