In France, Mother’s Day moves to the first Sunday in June when the last Sunday in May is Pentecost.
French Mother’s Day, or Fête des Mères, is normally held on the last Sunday of May. The exception prevents the two observances from falling on the same Sunday, so the celebration shifts one week later when Pentecost occupies the usual date.
The arrangement was established in postwar French law. A 24 May 1950 law set the last Sunday of May as the official date and explicitly provided for a move to the first Sunday of June when Pentecost coincided with it. The holiday was later incorporated into France’s social and family-policy framework.
Pentecost is a Christian feast observed seven weeks after Easter, so its date changes every year. That is why French Mother’s Day can fall in late May in one year and early June in another. Ascension Day is also a movable Christian feast, but it is not the trigger named in the French rule.