I'd like to get a multiple rather than single

 

First trip October

 

*Dec Apply O extension

*Jan PU extension

 

Second trip March, return late March

 

Possible with the above?

A reentry permit (whether single or multiple) is tied to your current permission to stay, and will expire at the same time as that permission to stay.

The above is correct. Another way of l0oking at it is that an extension of your permission to stay invalidates any previous re-entry permit you hold.

When you buy a Re-Entry Permit it protects your current Permission to stay. 

Buying a multiple-entry Re-Entry Permit (3.800,- THB) is only financially beneficial when you foresee at the moment you buy it, to exit Thailand at least 3 times during the remaining period of your Permission to stay.  Unless you foresee to make multiple exits/returns, buying a Single-Entry Re-Entry Permit (1.000,- THB) is cheaper.  You can buy a Re-Entry Permit at the Immigration desk in all major international Thai airports, so unless you are exiting Thailand at a land-border there is no need to visit your local Imm Office to buy it.

you need a single entry re-entry permit now for the October trip, and another after the new extension stamp and depending on overseas trips either single or multi

3 hours ago, Red Phoenix said:

Buying a multiple-entry Re-Entry Permit (3.800,- THB) is only financially beneficial when you foresee at the moment you buy it, to exit Thailand at least 3 times

Actually it should be "at least 4 times", 3 times would not be financially beneficial

 

Also what you fail to take into account is passport pages, they are valuable in and within themselves

 

Thanks everyone. I'd thought it die with my extension but hoping it was good for 365 days.

ERRRRR!!!!!!

 

could it be for 12 months ???? or when your visa expires

1 hour ago, blackshadow said:

ERRRRR!!!!!!

 

could it be for 12 months ???? or when your visa expires

It could be 12 months. It could be less. It all depends on the expiry date of your permission to stay. Under no circumstances will it depend on any visa you currently or previously held.