Would be grateful for an answer to the following question. I think I know the answer but just want to check beforehand.

Exit Thailand Sat 1/9...Return 10/9

12 month Visa expires 19/9 (obviously, will get 12 month visa extension sometime between 10/9 and 13/10)

Exit Thailand again Sun 15/10...Return 21/10

The question is do I need to get 2 x single re-entry, or can I get a multi re-entry to cover both trips?

Cheers.(in advance)

The re-entry permit is only valid for the duration of your curent permisison to stay, so in your plan a multiple entry is no good.

You can extend your permisison to stay up to 30 days early, your extension will still start when your current permisison to stay ends so you don't lose anydays. So if you go to immigration after 19/8 and extend you can also get a multiple re-entry permit, all in one go.

(Single is 1,000 and multiple 3,800).

Thak you very much Mario. That's clear:-)

Now that the OP has been given good advice (extend early, get a multiple re-entry), I'd like to pursue a certain detail that I've been curious about.

Let's say I'm on a 1 year extension and I have an unused single re-entry stamp. I go to Immigration a month early for renewal. With that renewal done, I believe that my single-entry permit has become invalidated. Even if I want to go somewhere right away (still within the original validity of that permit) for a quick trip, I need to get a new re-entry permit that matches my new extension date.

If that scenario is true (is it?), then instead of saying "your extension will still start when your current permission to stay ends", it think it is slightly more accurate to say "your extension will include any days you might have lost by renewing early". I realize that the difference is of no importance to those who always buy multiple re-entry permits.

The re-entry permit is only valid for the current extension permitted to stay stamp it was issued on so when you get a new extension stamp that will require a new re-entry permit. Believe it we keep that in mind we will be safe. You could say 'lost days' that but we have enough trouble trying to define visa and extension of stay - hate to take things any further.