When should I report my 90-day stay in Thailand after leaving and re-entering?

90 days from when you last entered

This is how it works,

- IF you stay IN thailand for 90 days you have to report.

- IF you leave thailand before your next 90 day report due date, the count down stops and when you come back you start counting fresh with your NEXT 90 day report being due 89 days from the date you stamped in

SO

In your case, your NEXT 90 day report is due 89 days from the date you stamped in 🙂