Is a 13 month extension possible (based on retirement)? Each year I get a 12 month extension, based on retirement, to my non-imm. visa. I read somewhere, cannot recall where, that for an additional 1000 baht to the normal fee, the 12 month extension can be incresed to 13 months.

Extended at the end of the 12 months by 1 month

There is no such extension of stay and all extensions of stay cost 1,900 baht and use the same TM.7 form.