Do I need to cancel my student visa at immigration before leaving Thailand?

* did you have to cancel your visa at immigration before leaving?

-> Yes, as a rule, you should cancel your extension before leaving Thailand IF you are already on an extension after the initial 90 days directly from a Non-ED visa.

If you are still on the first 90 days of an initial Non-ED visa, you can just leave and forget those worries.

* if you don’t cancel, you might be denied entry once you try to re enter on another visa

-> You read something confusing. You wouldn't be denied entry just because you didn't cancel your previous extension based on study. But you would have issues when you apply for a new visa or extension INSIDE Thailand.

* as you will be considered as overstayed for not cancelling the previous visa before you left.

-> When you apply for a visa or extension at the local immigration office with an un-cancelled extension, you would be fined for not cancelling properly, same rate as overstaying.

* after cancellation, how many days were you allowed to stay in Thailand before leaving?

-> You go to the immigration office that issued your extension bringing a termination letter from your school to cancel your current extension. The cancellation is effective as of the date on the termination letter. No extra days from that date. If you go to the local office on the last day, you have to leave within that day. Most offices accept cancellation applications in advance for a few days up to a few weeks depending on the office, then you can get some days before leaving.

Just an additional note.

If you want to bounce at a land border, they won't let you leave Thailand if you are with one of these (not an issue when leaving by air):

- an extension based on studying has not been cancelled

- you are on a 7-days-to-leave-kingdom stamp after cancelling an extension

OK, if you are still on an actual VISA, then that does not need cancelling. If you are on an extension of stay, that does need to be cancelled. You need to get a letter from your education provider stating your last day of classes, take that to immigration and cancel your extension, (this can be post dated). As for staying after the cancellation, you can buy a 7 day 'get out of the country' extension for 1900 baht.