The 90/180-day rule means you can stay in the Schengen Area, including the Netherlands, for a maximum of 90 days within any 180-day period. The 180 days are counted backward from each day of your stay. This rule applies to all Schengen countries together, not separately. If you spend 90 days in one Schengen country, you must leave and wait until you become eligible again. Staying beyond the allowed period can result in fines, deportation, or travel bans.