@Alexander ************
Keep at 89 days maximum. Do not count 90 days the way most people do. The way of counting is each day you're in Thailand is counted, NOT the number of nights you spend.
For example : if you get stamped in an hour before midnight, then THAT day is already counted, even if there is only 1 hour left. Same with stamping out an hour after midnight. It's a mistake many people make.