What are the consequences of overstaying a METV visa in Thailand, specifically regarding the 1-year ban?

In another forum I have been stuck giving overstay advice. My first advice had been to come here and get better advice than I could provide, but that did not happen. The OP in that forum did not understand his METV and has a significant overstay. The OP plans to fly to Malaysia tomorrow. I have not gotten a proper answer to my question about his permission to stay date but based on his entry date of Nov 9 I calculate it to be Jan 7. If so I thinking he is flying out on day 90. What I do not know is whether the 1 year ban starts on day 90 of overstay or day 91? Thanks for your input.