When should I file my 90-day report in Thailand: from my arrival date or my Non-O visa stamp?

your 90 day reporting starts when you get a visa or extension that LETS you stay more than 90 days in thailand.

So entering visa exempt for 45 days doesn't start the count down,

Getting a 30 day extension doesn't start the count down,

Getting a 90 day non-O VISA doesn't start the count down (because you can't stay IN the country on that visa MORE than 90 days) 😮

It's the year extension that starts the 90 day count down process.

Your FIRST 90 day report is due 89 days from the date they stamped the year extension IN to your passport. That's how it works out

Check your passport to see if there is a 90 day report reciept

Your first 90 days report counting usually starts when your 1-year extension starts. When you apply for an extension, you may get a small slip showing your 90 days report due date on your passport. Check the exact date with your local immigration office when you apply for an extension in late July.