Western Easter Gauss Date Calculator
Calculate Gregorian Western Easter by the corrected Gregorian computus (Meeus/Jones/Butcher arithmetic); not Orthodox Easter or a Julian-calendar conversion.
Description
Calculate Gregorian Western Easter by the corrected Gregorian computus (Meeus/Jones/Butcher arithmetic); not Orthodox Easter or a Julian-calendar conversion.
Western Easter is determined by an ecclesiastical calendar rule rather than by observing the astronomical full moon directly. Gregorian computus uses a nineteen-year cycle together with century corrections.1
When to use this tool
Calculate Gregorian Western Easter by the corrected Gregorian computus (Meeus/Jones/Butcher arithmetic); not Orthodox Easter or a Julian-calendar conversion.
- Prepare the supplied year fields for this operation.
- Compare the complete example with the representation used by your own input before carrying the result into another step.
How to use the tool and how it works
- Enter year. Use the exact text syntax, units and index conventions explained below.
- Run the tool. If input validation fails, correct the supplied fields before interpreting any result.
- Read result.year, result.month, result.day, result.gregorianDate. Interpret false, null and empty lists using the distinctions below; they can be valid outputs.
Require integer year from 1583 through 4099. Calculate its nineteen-year remainder, century/year remainders and leap corrections, derive the ecclesiastical lunar and weekday offsets, apply the exceptional-date correction, then calculate March/April month and day. Return numeric components and a zero-padded Gregorian date.2
| Input field | Meaning and representation | Accepted input |
|---|---|---|
| year | year. | Integer from 1583 to 4099 inclusive |
| Output field | Interpretation |
|---|---|
| result | Object containing the named outputs below. |
| result.year | The year value under the stated formula or text convention. |
| result.month | The month value under the stated formula or text convention. |
| result.day | The day value under the stated formula or text convention. |
| result.gregorianDate | The gregorian date value under the stated formula or text convention. |
{
"input": {
"year": 2026
},
"output": {
"result": {
"year": 2026,
"month": 4,
"day": 5,
"gregorianDate": "2026-04-05"
}
}
}Limitations and assumptions
- The implementation uses a century-corrected Gregorian computus despite the Gauss wording in the ID. It does not calculate Orthodox Easter, astronomical lunar events or every local holiday-observance rule.
- Every declared top-level field is required and unexpected fields are rejected. Numeric inputs must be finite; ordinary text fields are bounded to 8,192 UTF-16 code units, with tighter operation-specific limits where stated.
- Ordinary string lists have at most 128 entries of at most 128 code units each; numeric lists and matrices have separate bounded size checks. Nonfinite results and excessively large serialized outputs are rejected.
- Indexes are zero-based and spans have an exclusive end unless explicitly stated otherwise. A valid false, null or empty-list result is distinct from malformed input.
Alternative or Complementary methods
Choose the intended ecclesiastical calendar convention before comparing dates. Use an astronomical ephemeris for observed lunar events and a jurisdiction-specific calendar for legal holiday observance; Gregorian computus answers a different question.
References
-
The Date of Easter: ecclesiastical calendar rules — U.S. Naval Observatory
-
Tool behavior and example: Western Easter Gauss Date Calculator — tool.io
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