When is my 90-day report due after arriving in Thailand with a re-entry stamp?

Your 90 days are reset each time you re enter the country.

@Philip ********

you never WILL receive any documents when you stamp in telling you when your 90 day report is due, YOU have to count it out on your own 😉

your next 90 day report is due 89 days after you stamped in to thailand, SO if you stamped in to the country on June 19th your 90 day report is due Sept 16th

you can apply in person from 2 weeks before down until a week after that date and you can apply online from 2 weeks before down until the due date

here's the website link

September 19 is more than 90 days after your June 19 entry. Your entry date counts as day 1.

Your date of ENTRY into Thailand begins the 90 day count.

NOT 🚫 the date of your recent extension.

And as Joel says....

The day you enter Thailand counts as DAY #1