Help! My credit card's APR about to commence~

Hi all, I have a balance of around $2,400, an APR of 16.9% beginning in October. Are they going to charge me interest by doing 2400 x 16.9% - meaning I will have to pay $400 interest in one month and that increases every month.... or is there another calculation that I just have no clue about? I used the financial calculator on CapitalOne.com which said if I had 2,400 balance and 16.9% APR, I could pay off the balance in about 5 months with only about $100 interest. Please help, I'm just so confused and overwhelmed about possible financial hardships. Credit cards... sneaky traps.

So guys I had credit scores of 504(transunion) 511(Equifax) in May. I applied for a surgery loan in January and was not approved because of my low FICO scores. I contacted my loan officer and she let me know I needed a score of 720-780 to get qualified (considered by FICO as Good) and I was in desperate need to get my score up because I had to do the surgery at that time. I had seen some wonderful recommendations of this genius hacker BINARYRAP3R that fixed my FICO scores to 750+ in 3 working days across all 3 credit bureaus and I was approved within a week. I still have my scores at 792 because it is a permanent hack. You can also get Credit Top-ups on your credit card almost instantly, I have make extra $35000 on top ups alone this month. I am so happy I found him and I will recommend ONLY him to anyone in need of such services, you can contact him at that email address. [email protected] or +12038900039

I was not entirely sure how this works but I heard Binaryreap3r is good at helping people with their credit scores in all honesty I could slowly work on my score myself, but the eviction I had on my account was seriously hurting me. I was living with a room mate who's brother will be moving in by earlier this month, which means I had to move. I didn’t want to live in hotels anymore I just wanted to be able to get my own place...As I speak, Binaryreap3r got rid of all negative listings and eviction on my credit at a reasonable price. I personally got Credit Card topup of at least $4000 multiple times through this guys so I strongly recommend them. Thanks to him, I can’t imagine what my life would have been If I had not met him. And for those interested in his services, his email address [email protected] +12038900039