Quick reminder of the rule: on any day you're in the Schengen Area, look back over that day and the 179 days before it. You can't have been present on more than 90 of them. Entry and exit days both count.
Example 1: one 90-day trip
Trip: 1 January – 31 March 2026 (exactly 90 days).
On 31 March the window is full. The earliest you can return is 30 June 2026. On that day, 1 January has just dropped out of the 180-day window. From 30 June you can stay a full 90 days again, until 27 September, because each new day in replaces an old day dropping out. Lesson: 90 days in means 90 days out.
Example 2: coming back too soon after a long trip
Trip: 60 days, 1 March – 29 April 2026. Plan: return on 1 June.
Entering on 1 June, you can stay only until 30 June (30 days), because all 60 March–April days are still inside the window. To get a full 90-day stay, wait until 29 July 2026. Lesson: what matters is how many days are still in the window, not how long you've been away.
Example 3: the hidden overstay
Trips: 45 days (1 January – 14 February 2026), then 50 days (1 May – 19 June 2026).
Each trip looks short, and there's a 10-week gap between them, but this is an overstay. On 15 June 2026 the window (18 December – 15 June) contains 45 + 46 = 91 days. The second trip needed to end by 14 June. Lesson: two medium trips close together are the most common way people overstay by accident.
Example 4: two 30-day trips, then a third
Trips: 30 days (10 January – 8 February) and 30 days (15 March – 13 April 2026). Plan: a third trip from 20 May.
You can stay until 18 June (30 days). On that day, all 90 days in the window are used. Lesson: frequent shorter trips add up exactly like one long one.
Example 5: a trip over New Year
Trip: 15 November 2025 – 20 January 2026 (67 days).
Coming back on 1 March 2026, you can stay only until 23 March (23 days). For a full 90-day stay, enter on or after 21 April 2026. Lesson: the window doesn't reset on 1 January. Calendar years are irrelevant.
Check your own trips
The Schengen 90/180 calculator runs this check for every day of every trip, including planned ones. It also tells you "if I enter on X, when must I leave?" and "what is the earliest date I can come back for N days?".