If you fail to report to Immigration in the 3-week window, you will be fined 2,000 THB. Continuing to ignore the report will increase your penalty the longer you go without doing it. Furthermore, if you are detained by Thai police or Immigration and you are found to have not reported in time, the fee increases to 5,000.
Repeated or serious offenses regarding your 90-day report can, in extreme cases, lead to deportation and blacklisting.
The ask:thailand community, consisting of multiple Q/A groups with over 100,000 members, powers this platform. It is not an official government resource. Our members actively contribute to this resource, and while we strive for accuracy, we cannot guarantee its complete reliability. Assistance to travelers is provided as a community service.