The title basically says it all: I entered Thailand from MAS on 18 March. 90 Day reporting online hasn't worked. So my only options left are leaving Thailand or heading for immigration. With my visa MUST I leave the country? All my colleagues have single entry visas, so I can't take their word that reporting is sufficient.

If you have an extension of stay issued by your local immigration office you can report at the office in person (or by proxy), within 15 days before or 7 days after the 90th day (June 15th). That means you need to report on or before June 21st. You don't need to leave the country until your permit to stay (extension) expires.

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Extension of stay of Non-B + multiple entry permit

 

22 hours ago, MarcelV said:

I entered Thailand from MAS on 18 March

 

22 hours ago, MarcelV said:

With my visa MUST I leave the country?

You're talking about extensions of stay, and visas and multiple entry permits (presumably you mean re-entry permit). The assumption is that you mean you have an extension of stay (not a visa) and a re-entry permit.Or do you mean you have a multiple entry visa?

 

If you have a valid extension of stay issued in Thailand at an immigration office, you need to report every 90 days, but don't need to leave the country. If you have a multi-entry visa issued by a Thai embassy or consulate outside Thailand, you would need to leave the country and return.

 

One way or the other you should have a permission to stay stamp in your passport. It indicates by when you need to exit.