Does a stay count as date of check in or check out

So apologies - I'm sure this is easy to find obvious information but I couldn't easily see in searching.

I need one more stay for Gold by 17th Feb - my next stay unless something crops up is the 17th of feb - checking out 18th - so will this count?!? I am hopeful that another trip will materialise before then but want to see if I need to find a cheap deal somewhere!!

Thanks in advance