In the Schengen Area, most short-stay visitors may stay for a maximum of 90 days in any rolling 180-day period. On each day of the stay, you look back 180 days and add every day spent in Schengen; that total must not exceed 90. Entry and exit days both count, and moving between Schengen countries does not reset the clock.
Holders of an EU residence permit or a long-stay (D) visa are not under this short-stay limit for those stays. The European Commission publishes an official short-stay calculator to check compliance or plan future travel.
Source: Short-stay calculator — European Commission (Migration and Home Affairs)