A third country national may stay in the Schengen area for no more than 90 days in any 180 day period. It is a rolling window, not a calendar year, so days from the previous autumn still count against a trip in spring. Both the date of entry and the date of exit count as full days of stay, which makes a long weekend four days rather than two.
Where this comes from: art. 6(1) Regulation (EU) 2016/399 (Schengen Borders Code), EUR-Lex, Official Journal, read 2026-09-07; art. 6(2) Regulation (EU) 2016/399 (Schengen Borders Code), EUR-Lex, Official Journal, read 2026-09-07.