What are the requirements for showing funds to Thai immigration after receiving a retirement extension?

See my updated reply .. Jomtien immigration ONLY requires bank book update. . NOT a letter.

My apology to the OP... As I at first thought his question was about the amount of Thai baht needed to be shown in his Thai bank account... and for how long. Hopefully he now has his answers. BUT as it's Jomtien Immigration office, it's always BEST to ask them

You need a letter from the bank.

I hope this helps you understand better the requirements ..

AND it's important that you ASK YOUR LOCAL THAI IMMIGRATION OFFICE... for their requirements

You asked a similar question which I replied to by PM personal message...

Please Ask your local Thai immigration office what they REQUIRE following the approval of your one year extension of stay as retired. .

NOT all offices require PROOF of a bank statement balance of 800,000 Thai baht at 90 days ..

BUT it's required that you keep the 800,000 for the first 3 mm months after extension approval, not less than 400,000 Thai baht in the next 7 months and again 800,000 Thai baht in the final 2 months before your next One year extension of stay.

Failure to meet the requirements can mean you are on OVERSTAY during the time you have not kept the balances as you agreed to when you were granted the extension. . and be DENIED your next extension of stay

Ask the immigration office. They will give you a list of required docs.