{"success":true,"version":"v1","request":{"tool":"get_calculator_schema","calculator_id":"easter-date"},"result":{"entity_type":"calculator","id":"easter-date","calculator_id":"easter-date","canonical_url":"https://tttkmbb.com/time/easter-date","name":"Easter Date Calculator","title":"Easter Date Calculator – Gregorian (Meeus/Jones/Butcher) and Orthodox Easter with Lent and Pentecost Dates","category":"time","category_name":"Time & Geography","tool_name":"calculate_easter_date","featured_mcp_tool":false,"description":"Computes the date of Western (Gregorian) Easter Sunday for any year with the Meeus/Jones/Butcher algorithm and derives Ash Wednesday, Palm Sunday, Good Friday, Ascension Day and Pentecost; also gives Orthodox Easter from the Julian computus converted to the Gregorian calendar.","use_when":"You need Easter or the movable feasts tied to it (Lent, Holy Week, Ascension, Pentecost) for a year, including the Orthodox date.","do_not_use_when":"You need fixed-date holidays or non-Christian movable holidays (Passover, Ramadan, Diwali), or dates before 1583 when the Gregorian calendar did not exist.","inputs":[{"name":"year","label":"Year","type":"integer","required":true,"min":1583,"max":4099,"description":"Gregorian calendar year.","example":2026}],"outputs":[{"name":"easter_sunday","label":"Easter Sunday","type":"date","decimals":4,"description":"Western (Gregorian) Easter."},{"name":"ash_wednesday","label":"Ash Wednesday","type":"date","decimals":4,"description":"Easter − 46 days; start of Lent."},{"name":"palm_sunday","label":"Palm Sunday","type":"date","decimals":4,"description":"Easter − 7 days."},{"name":"good_friday","label":"Good Friday","type":"date","decimals":4,"description":"Easter − 2 days."},{"name":"ascension_day","label":"Ascension Day","type":"date","decimals":4,"description":"Easter + 39 days (a Thursday)."},{"name":"pentecost_sunday","label":"Pentecost (Whit Sunday)","type":"date","decimals":4,"description":"Easter + 49 days."},{"name":"orthodox_easter","label":"Orthodox Easter","type":"date","decimals":4,"description":"Eastern Orthodox Easter (Julian computus) expressed as a Gregorian date."},{"name":"orthodox_offset_days","label":"Orthodox − Western","type":"integer","unit":"days","decimals":4,"description":"Days by which Orthodox Easter follows Western Easter (0 when they coincide)."},{"name":"golden_number","label":"Golden number","type":"integer","decimals":4,"description":"Position of the year in the 19-year Metonic cycle: (year mod 19) + 1."}],"input_schema":{"type":"object","properties":{"year":{"description":"Gregorian calendar year.","type":"integer","minimum":1583,"maximum":4099,"examples":[2026]}},"additionalProperties":false,"required":["year"]},"output_schema":{"type":"object","properties":{"easter_sunday":{"description":"Western (Gregorian) Easter.","type":"string","format":"date"},"ash_wednesday":{"description":"Easter − 46 days; start of Lent.","type":"string","format":"date"},"palm_sunday":{"description":"Easter − 7 days.","type":"string","format":"date"},"good_friday":{"description":"Easter − 2 days.","type":"string","format":"date"},"ascension_day":{"description":"Easter + 39 days (a Thursday).","type":"string","format":"date"},"pentecost_sunday":{"description":"Easter + 49 days.","type":"string","format":"date"},"orthodox_easter":{"description":"Eastern Orthodox Easter (Julian computus) expressed as a Gregorian date.","type":"string","format":"date"},"orthodox_offset_days":{"description":"Days by which Orthodox Easter follows Western Easter (0 when they coincide). Unit: days.","type":"integer","x-unit":"days"},"golden_number":{"description":"Position of the year in the 19-year Metonic cycle: (year mod 19) + 1.","type":"integer"}}},"formula":"Meeus/Jones/Butcher: a = Y mod 19, b = ⌊Y/100⌋, c = Y mod 100, d = ⌊b/4⌋, e = b mod 4, f = ⌊(b+8)/25⌋, g = ⌊(b−f+1)/3⌋, h = (19a+b−d−g+15) mod 30, i = ⌊c/4⌋, k = c mod 4, l = (32+2e+2i−h−k) mod 7, m = ⌊(a+11h+22l)/451⌋; month = ⌊(h+l−7m+114)/31⌋, day = ((h+l−7m+114) mod 31)+1. Orthodox: Meeus Julian algorithm, then Julian date + (⌊Y/100⌋ − ⌊Y/400⌋ − 2) days","method":"Easter is the first Sunday after the ecclesiastical full moon on or after 21 March; the tabular algorithms reproduce the Gregorian and Julian computus exactly for all years. The Julian-to-Gregorian shift is 13 days for 1900–2099.","sources":[{"name":"Date of Easter – Anonymous Gregorian algorithm and Meeus's Julian algorithm (Wikipedia)","url":"https://en.wikipedia.org/wiki/Date_of_Easter","type":"reference","retrieved_at":"2026-09-24"},{"name":"USNO Astronomical Applications – The Date of Easter","url":"https://aa.usno.navy.mil/faq/easter","type":"government","retrieved_at":"2026-09-24"}],"freshness":{"type":"static","max_age_seconds":null,"note":"Deterministic formula with fixed constants; results never go stale. Inputs supplied by the caller determine the output."},"examples":[{"name":"2026","inputs":{"year":2026},"expected":{"easter_sunday":"2026-04-05","ash_wednesday":"2026-02-18","palm_sunday":"2026-03-29","good_friday":"2026-04-03","ascension_day":"2026-05-14","pentecost_sunday":"2026-05-24","orthodox_easter":"2026-04-12","orthodox_offset_days":7,"golden_number":13},"url":"https://tttkmbb.com/api/v1/calculate/easter-date?year=2026"},{"name":"2025 (Western and Orthodox Easter coincide)","inputs":{"year":2025},"expected":{"easter_sunday":"2025-04-20","orthodox_easter":"2025-04-20","orthodox_offset_days":0,"ash_wednesday":"2025-03-05"},"url":"https://tttkmbb.com/api/v1/calculate/easter-date?year=2025"}],"faq":[{"q":"Why do Western and Orthodox Easter differ?","a":"Orthodox churches keep the Julian calendar and its older lunar tables, so their Easter falls 0, 1, 4 or 5 weeks after the Gregorian date; the two coincide in years such as 2017 and 2025."},{"q":"What is the possible range of dates?","a":"Western Easter falls between 22 March and 25 April; Orthodox Easter between 4 April and 8 May (Gregorian) during the 20th–21st centuries."}],"tags":["easter date","when is easter","orthodox easter","ash wednesday","good friday","pentecost"],"related":[{"calculator_id":"days-until","reason":"Countdown from today to the Easter date."},{"calculator_id":"day-of-week","reason":"Weekday and ISO week of any of the feast dates."},{"calculator_id":"add-days","reason":"Shift a feast date by a number of days."}],"links":{"html":"https://tttkmbb.com/time/easter-date","markdown":"https://tttkmbb.com/time/easter-date.md","json":"https://tttkmbb.com/time/easter-date.json","api":"https://tttkmbb.com/api/v1/calculate/easter-date","schema":"https://tttkmbb.com/api/v1/calculators/easter-date","openapi":"https://tttkmbb.com/openapi.json","mcp":"https://tttkmbb.com/mcp"},"version":"v1","updated_at":"2026-09-24"},"timestamp":"2026-09-24T01:51:38Z"}