What are the implications of applying for a visa extension just before it expires in Thailand?

What visa do you have ?

Okay let's sort this out before this thread goes sideways with people whose intentions are good but information might not be 😮 🙂

First - doesn't matter when you apply for a 30 day extension on a 60 day free stamp or 60 day tourist visa entry, the 30 days is always added to the expiration date of the existing stamp. This means there is no advantage to burning down the stamp to the end because you don't lose days by applying early.. 🙂

As far as WHEN you can apply for the extension that is controlled by the immigration office you use (where you're staying in thailand)

Some offices (Bangkok, Chiang Mai, Samut Prakan, and others) allow you to apply when you have 45 days or less left on your stamp

Most other offices allow you to apply when you have 30 days or less left on your stamp

BUT

A few offices (notably; Jomtien & Samui) only allow you to apply when you have 7 days or less left on your stamp. <- I don't know why they're just renegade in that regard

Also just in case people are wondering

IF your current stamp expires on a day the immigration office is closed <- weekends or holidays, and you go the very next day they are open you can get your extension like normal, you will not be fined for overstay (you will get a stamp in your passport that says "overstay xx days fine waived due to closure") and that won't affect you entering or getting a visa, or getting an extension at all..

Best of luck to the O/P, just GO get the extension this or next week sometime and you'll be fine.

Where are you located ? I had a similar situation recently, was facing a one day overstay, went to Yasothon office and applied 30 day extension which officer said was a "good decision" to avoid a bad report on my file for future marriage visa process

1900 baht well invested

Your extension will start when your current stamp runs out so no time lost I would go now and extend it

I think you're confused a bit.

When you apply for a 30-day extension, that time is added to the expiration date of you current stamp

There is no benefit to wait until your stamp runs out to apply for the extension because you don't lose any time applying early.