When's my 90-day report due?

Pick one date and you get your due date, the filing window, and the one after. Free, and no sign-up.

Which have you done most recently?

I arrived in ThailandUse this if you haven't reported since your last arrival.I did a 90-day reportUse the date on your last 90-day slip.

Date you arrived

The short version

Who has to do a 90-day report?: Anyone who stays in Thailand for more than 90 days in a row: retirement, marriage, work, education, DTV and Privilege visa holders. LTR visa holders report once a year instead.
How are the 90 days counted?: The day you arrive is day 1, so your first report is due on day 90. After that, each report is due 90 days after the last one. Leaving Thailand resets the count.
What if I miss it?: The fine for a late report is 2,000 THB, and more if you're caught never having reported. Go to your immigration office as soon as you can.
Can I do it online?: Usually yes, from your second report on, at tm47.immigration.go.th. Your first report after arriving has to be in person.