How far in advance can I complete my 90-day reporting in Chiang Mai and what documents do I need to bring?

15 days before or 7 days after the due date, take your passport, a completed TM47 form in blue ink and a copy of your up to date TM30 if required, but always best to check with your local immigration office as it varies from office to office around the country

I just walk in to Immigration office near the airport in Chiang Mai). It is a drive through. You can walk in with passport and TM.30 and fill the form over-there. I get it done in 5 mins.

The window for 90-day reporting in person at the immigration office is between 15 days before and 7 days after the due date.

Usually, you need an original and copy of your passport, filled TM.47 form, and TM.30 receipt, But these vary hugely by office.

I think Chiang Mai requires less.

Let's see what actually the Chiang Mai office requires you from others in CM.