My TR says I can stay until August 4th. If I leave on August 4th no problem right?

You mean the permitted to stay until stamp in your passport from Immigration? You have to leave on that day or before so yes you can leave on that day. If you are talking about the actual visa from a Consulate that date is a enter before date and once here/used has no significance.

Yes you have to leave on or before the date stamped in your passport by Immigration when you arrived.

You can also leave after that date as long as you pay for overstay - 500bht per day

You can also go to jail for overstay so it is not recommended.

You can also go to jail for overstay so it is not recommended.

Good answer Lop.

I was one day over, due to a flight being cancelled. rang the immigration and they said not to worry as long as I left within 24 hours of the date there would be no charge.

Got to the airport and no problem being the day late and did not have to pay anything, they just stamped the passport accordingly.

Thanks Lioness , thats what I was meaning , overstay 1 or 2 days generally no problem. Stay longer and you can go to jail agreed. If you are going to overstay , I recommend what Lioness has done , contact immigration and explain the reason and see what they say , preferably before you overstay. Make sure you get someones name for reference just incase .

Exiting the airport on overstay is not a problem. The problem will be if you get stopped by the police before you get to the airport. Unlikely but possible.