Just opened AmEx Blue preferred checking my statement and all the info on it see a section about trailing interest. About Trailing Interest You may see interest on your next statement even if you pay the new balance in full and on time and make no new charges. This is called "trailing interest." Trailing interest is the interest charged when, for example, you didn't pay your previous balance in full. When that happens we charge interest from the first day of the billing period until we receive your payment in full. You can avoid paying interest on purchases by paying your balance in full and on time each month."

I'm coming from a citi Costco card. I checked my statement from there and in 2018 I paid ZERO interest despite using it for basically 100% of my purchases. I was not in a promotional zero interest period either I've had that card for 3 years.

So I always pay my STATEMENT BALANCE in full a few days prior to the due date. I googled it and people are saying that the interest accrues from the close of the period to the moment you pay even if it's ON TIME, that interest accrued will get added to the next statement. So if my closing date is the 15th should I go in on the 14th and pay my balance in full to avoid any interest charges? Is this different with AMEX?

I'd rather not pay it before the close date because I use auto pay and I'm lazy and also sometimes I won't be able to afford it. I got a routine and a tight budget.