First off, I've spent an hour trying to find this answer on existing threads, but haven't, and my internet connection is very slow today.

This post already took 2 attempts.

So I start this new thread, and it might be helpful for others, newbies, as well.

I have single entry Non Imm B visa and the stamp says "Valid Until: 20 March 2016".

Now, I want to exit Thailand on THAT date, and I just want to make sure that the visa is

in fact still valid on that date, 20 March 2016, and until midnight on that date (although I plan

to exit some time in the afternoon, at land border crossing).

So, if the visa is valid until 20 March, I can exit without problem (i.e. overstay issue) on 20 March?

Thanks!

Yes you can leave on the 20th anytime before midnight.

p.s. I assume that when you stay "stamp' you are referring to the entry stamp admitting to you until Mar 20th.

Once you enter the country the date on your visa does not matter. The admitted until date on the entry stamp immigration did when you arrived is the one that is important.

^^ Thank you both for the confirmation, that I can exit on that date without issue.