@Chris ********
It’s all about the terminology, folks!
You apply for a 90 days Non-imm-O retirement visa in the UK
You enter Thailand and will get stamped in for a 90-days stay permit.
The visa will expire upon entry!
From up to 30 days before the 90-days stay permit expires, you can apply for the “1-year extension of the stay permit”.
Thai Immigration calls it “visa extension” but this is just bad English. They don’t extend any non-existent visa, they just extend your stay permit.
At the day of your application to the 1-year Extension, they 800.000.- THB must have been sitting in your Thai bank account for 2 months, and you need to prove this with the “bank letter of guarantee” (in Thai: rab roong thanakan)
After being issued the one-year Retirement Extension, a minimum of 800.000.- THB must remain in your account for at least three months. After this, you could theoretically take money out but there must always be 400.000 THB left in the account.
And two months before your next application for a NEW (!) 1-year Extension of Stay Permit, a minimum of 800.000.- THB must be back in your account
You do not need to apply for a new 90-days Non-Imm-O Retirement visa. You just “renew” the yearly “Extension of Stay”
The moment when Immigration issues the Extension, ALWAYS buy a single re-entry permit for 1000.- THB for this one-year extended stay permit. Bring at least two passport pictures for this permit. Because if you exit Thailand during this one year, the re-entry permit keeps your stay permit alive, for one single re-entry
Should you plan to exit Thailand more often than three times in one year, then buy a multi re-entry permit for 3800.- THB. It allows you unlimited re-entries into Thailand