Dates defined as an offset from Easter — the largest moveable family in the corpus.
A great many observances are defined not by their own date but as a number of days from Easter. Good Friday is Easter minus two; Easter Monday is plus one; Ascension is plus thirty-nine; Carnival Monday is minus forty-eight.
Storing them as offsets rather than dates is the only way to keep them correct across years, and it is how the corpus holds them — 579 rules relative to the Western computus and 36 relative to the Orthodox one.
The offsets also travel further than the religion does. Carnival is a public holiday across Latin America and the Caribbean, and its date is fixed by an ecclesiastical calculation regardless of what any individual observer believes.
The same offset — forty-eight days before Easter — in three countries, computed from the Western reckoning.
| 🇦🇷 | Monday 8 February 2027Argentina | Carnival MondayEaster minus 48. |
| 🇧🇴 | Monday 8 February 2027Bolivia | Carnival MondayThe same rule, the same day. |
| 🇩🇲 | Monday 8 February 2027Dominica | Carnival MondayAnd in the Caribbean, from the same calculation. |
Computus produces the date of Easter. These rules are offsets applied to whatever it produces.
See also computus · moveable feast · fixed date rule · nth weekday rule
We hold this as rule_type: relative_to_easter — 579 rules — and relative_to_orthodox_easter — 36. See what we hold.