the 400k are already in the bank for 3+ months when doing my renewal this year. But usually you get 1 month and then you need to come back to stamp the other 11 months. Do the 400k need to remain in the bank during this 1 month period?

Prior to the establishment of the 2/3 month system it did - we have no firm information on it now that I am aware of but have seen reports of it being used without an issue so do not believe there is a further check anymore.

I always dip into it during that month with no problem. So far.

^yeah, me too...I was afraid that it might be an issue but that would necessarily involve verifying the bank details again when returning to the immigration office for the final stamp after the 30 day waiting period and that is not required...thus far

Thanks for all your replies The past 2 or 3 years (been staying in Thailand too long, can't remember how many) I've always let the 400k in the account for another month untouched until I got the remaining 11 months, but I would think that they don't call the bank to ask for the balance. That would require some kind of authorization, though in Thailand I wouldn't be surprised if the bank gave information to Immigration without authorization. I'll give it a try this time and dip into it.

In the past you signed an authorization paper (in Thai) during the application process from what some reported. I know for a fact that many people did have accounts checked and were not approved until the balance was at the required level (often after they asked why it was taking so long).

As said do not believe that is the normal procedure since the requirement to have in account early took place.

No, the one month is only to process the paper work. After you have submitted the visa application and are told to come back in one month, you can take your money out safely.