If you are a foreigner staying in Thailand for a period longer than 90 days holding a Non-Immigrant Visa, you are required by Thai Immigration to report your current address every 90 days.
You must file this report within 7 days before, or 7 days after, your 90-day period expires. However, if you leave Thailand anytime during the 90-day period, then the day count will restart from 1 upon your re-entry into Thailand.
Applying for your first 90-day extension counts as your first 90-day report. Filing the 90-day report is fairly easy. You can report to Thai Immigration either in person, or you can authorize someone to report for you. You can even send the notification via registered mail.
You can file your 90-day report (or authorize someone to file for you) at any of the following locations:
Counter 3, Immigration Bureau Office, Soi Suanphlu, Bangkok
Visa extension units, Ratchada Centre (BOI)
Immigration offices throughout the country
If you would like to report to Thai Immigration via registered mail, you will need to send the following required documents:
Copy of all passport pages (up to the latest arrival stamp in the Kingdom or latest visa stamp)
Copy of arrival/departure card TM. 6 (front and back)
Previous notifications of staying over 90 days (if any)
Completely filled in and signed notification form TM. 47
Envelope with 5 Baht stamp affixed and return address of foreigner for the officer in charge to send back the lower part of form TM. 47 after having received the notification. This part must be kept for reference and for future notifications of staying over 90 days.
You must then send these documents to this address, keeping in mind that they should arrive 7 days before your 90-day period expires:
90 DAYS REGISTRATION, ROOM 206
507 SOI SUANPLU, SOUTH SATHORN RD.,
Please note that you have to keep the receipt of the registration for verification purposes when sending registered mail.
It is better to keep track of the rules of Thai Immigration at all times during your stay in the country, as failure to file your 90-day report can result in a fine of 2,000 THB, and can increase to up to 5,000 THB once you get arrested.