Some destinations have a "90/180 rule" which says you can come and go but you must not spend over 90 days out of any 180 days in the area. A recent question asked by a new contributor concerns this rule.
At least Schengen and Turkey have this rule, probably depending on where the traveller is from and what kind of visa they apply for.
Maybe I'm a dummy but I've always had a lot of trouble trying to add up how many days I've spent in such places when I've entered and left several times over recent months.
Is there a really way to do this I'm missing or is it difficult for everybody? I'm guessing something based on counting backwards from the end date might be the trick?
Maybe you know of an app or website that can do this for you.