How can a US citizen extend their 45-day visa while in Chiang Mai, Thailand?

every Immigration office is not the same as the others the Thailand...some you can go the same day as you land for a 30 day extension, some you have to wait until you're close to the end of your 45 day stamp...but they all cost the same 1,900 THB for a 30 day extension...good luck

Passport

Fill out form TM7 (available at the office)

Copy passport data page (signed by you)

Copy of entry stamp (signed by you)

Copy of your visa - either the sticker in your passport or pdf evisa (the former signed by you). * if you had one.

Copy of TM6 departure card (signed by you) *if you were issued one - if you entered by air after July ‘22 you wouldn’t have been given one so leave the space on the form blank.

Passport photo (most offices have facilities on site or nearby)

1,900 baht

Chiang Mai will ask for a TM30 (shows you are staying in the province) which your hotel or landlord should have filed on your behalf. A screenshot of their filing it online will suffice as evidence you have one.

There's no such thing as a 45 day visa. You entered visa exempt which means you have no visa at all.

You would go to the Chiang Mai immigration office for your one time 30 day extension. Chiang Mai requires a TM30 so you'll need to ask your landlord or hotel for proof of it to print before you go. You can go anytime as the days will be added on to the end of your current stay.