The nature of the 90/180 rule is vital to know for multiple-entry visa holders. Most people believe the 180-day period begins when your visa is issued, but it begins when your visa is issued. This means you must calculate backward from the day you plan to re-enter the Schengen Area to ensure you haven't spent more than 90 days there in the previous 180 days.

Another point that most multiple-entry Schengen visa holders and nationals of countries that are allowed to enter Schengen visa-free get puzzled about. The 180-day period does not begin on the day your visa becomes valid, as most people believe.

The 180-day term continues to run. As a result, whenever you want to enter the Schengen area, all you have to do is count backward 180 days and see if you were present in the Schengen area for more than 90 days at that time.