In Western Christianity, Easter is observed on the first Sunday after the first full moon on or after the ecclesiastical spring equinox marker. Because that formula depends on both the weekly cycle and a lunar marker, the result shifts from year to year.
The equinox used for the calculation is not re-measured by local astronomy in each country. Instead, churches use an ecclesiastical framework so that the festival can be calculated consistently for calendars and liturgical planning.
For most readers, the practical outcome matters more than the technical formula: Easter can land in late March or any part of April, which affects school breaks, travel, church schedules, and related holidays such as Good Friday and Easter Monday.