If you're a non-EU citizen visiting the Schengen Area, you can stay for a maximum of 90 days within any 180-day period.
The tricky part: the 180-day window is rolling — it moves forward every single day, not a fixed calendar period.
Example: You enter France on Jan 1st and stay 30 days. On Feb 1st, the 180-day window runs from Aug 5th to Feb 1st. Only days within that window count toward your 90-day limit.
As time passes, older trips "drop off" the window and free up your allowance again.
Who does this apply to? Citizens of visa-free countries — USA, UK, Australia, Canada, Brazil, Japan, and many others.
What happens if you overstay? Fines, denial of entry on future visits, or a temporary ban from the Schengen Area.
The 27 Schengen countries: Austria, Belgium, Croatia, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Italy, Latvia, Liechtenstein, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia, Slovenia, Spain, Sweden, Switzerland.