Can I extend my visa on the last day before expiration in Bangkok?

Never wait for the last day to renew.

Don't leave it so late next time as you lose nothing going early, the 30 days is added to your current exit date

@Gabrielė ********

You can do on 17th, but expect long queues after holiday closures, sorry

You can do on 17th, but expect long queues after holiday closures

My opinion depending where you will be when you want to go to the office. Go to a smaller town. We first tried at a really big city it was totally mad super busy and they said they didn't have time to do today and to come back another day before expiry. So next time we tried we were staying in quite a small area in comparison and that office was a breeze super helpful and in and out within 20 minutes. However we did have all the paperwork ready to go.

Many offices will be super busy on the 17th because of the 5 day closure. Probably best to go early

You can go on 17.

Yes you can as long as you’re not on overstay. Some immigrations also just accept extensions within the last week, and they understand the Songkran thing.