If you go the fixed amount in the bank route you will need to have the 800k in a thai bank for 2 months before the retirement visa but you can only open a bank account if you have a long term visa such as an O-visa or an OA-visa, there is also the monthly income route. The O-visa doesn't require the medical insurance that is needed for the OA-visa so that it the best one in my opinion. Most people come to Thailand on the O-visa and immediately open a bank account then transfer the funds and for the first application the money needs to be in the bank for 2 months and you have 3 months from arrival so you can apply before you have to extend or leave Thailand. Check the details on the Pattaya expat club website (
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as they are normally very useful and tend to be up to date as things do change.