If something is valid until the 23rd can I use it on the 23rd?

[NicoAndTheNiners]

Or does it run out today.

Annual train pass which says “valid until 23rd of August 2018”.

I reckon that means it’s still valid tomorrow, dd says not.

Yep valid until (the end of) the 23rd.

Yes, valid until tomorrow.

Thanks, will tell dd to catch the train and stop flapping!