I'm in a bit of a pickle. This is the first 90 days after I got my 1 year B visa with multiple entry. For a number of different reasons I missed the deadline to do the border crossing when it was due yesterday, the 25th. (I'm a US passport holder.)

So now I need to fix it. I was told that if I can get a flight out today, I won't have to pay the 500B fee (although I have also heard that they stopped doing that and I still would have to pay the fee). I can fly to KL but it will cost more than twice as much as doing a visa run to Cambodia tomorrow.

Since I've already screwed up do you think waiting an extra day will cause more of a problem?

It won't cause more of a problem, unless you get caught on overstay on the way to the border.

If you leave today by air you don' pay an overstay fine of 500 baht. if you leave tomorrow (by air or land)you pay 1,000 baht overstay fine.

Will the OP overstaying 90 days affect the remainder of the visa?

Actually he has only overstayed one day and there should not be any effect on future entries.

Thanks! I ended up deciding to go tomorrow.