<prompt> Human: Hello rpersonalfinance,I have a Chase Visa that I typically charge right around 1,800 a month on. Since I opened the card 2 years ago, I have paid the statement balance in full every month, as per the FAQ. I was not charged any purchase interest during this time. I made a typo in sending a payment last month, and was charged purchase interest for that billing cycle. I was pissed, but chalked it up as a lesson learned in paying more attention. This past month, I did pay the statement balance in full and then some, to clear some space from extra expenses due to a car repair, but was still charged interest. Here is what is going on: for the billing period from 122014 - 12115 my statement balance was 1,819.67, with a due date of 21715. I sent a payment of 1,800.00 on 2315.I meant to pay 1,820, but made a careless error. I was charged 14.26 purchase interest for this and my next statement was as follows: for the billing period from 12215 - 22015 my statement balance was 1,831.46, with a due date of 31715. I sent a payment of 2,600.00 on 030415.Today I looked at my statement for the billing period from 22115 - 32015 and saw that I was still charged 14.31 interest. What is going on? I know about average daily balance, but I figured that only started calculating after the 21 day grace period? Did that one month of failing to pay off the whole statement balance set something off? I thought it was as simple as pay statement balance by due date no purchase interest charges, but clearly not. Thanks in advance,Assistant: Nope. Nowadays they charge you based on the average daily balance of the two previous statements, not just one. You have fully pay off the statement for two months before it clears.Human: Thanks so much for the quick reply!Damn, if I had known I would have called the CC company last month and asked them for the pay off amount.But let me get this straight, once I pay this months statement balance in full, I will no longer be charged any purchase interest?  <response>: Call them and have them waive it for you, they should be able to do it depending on your payment historyrelationship with them. 