This tool converts dates between the Gregorian calendar and the Coptic calendar (Anno Martyrum / A.M.), the liturgical calendar of the Coptic Orthodox Church still used in Egypt and the calendar system also reflected in the Ethiopian calendar. It is useful for finding Coptic feast dates, reading historical ecclesiastical documents, or understanding when a Coptic date falls on the modern calendar. Conversions run both directions and are mathematically exact.
Structure of the Coptic calendar
The Coptic calendar is ancient and remarkably consistent. Its structure:
- 12 months of exactly 30 days each, giving 360 days in the main calendar.
- A 13th month, Nasie (the epagomenal days), of 5 days — or 6 days in a Coptic leap year.
- Leap year rule: a Coptic year is a leap year when the year number mod 4 equals 3 (one year before a Gregorian leap year in most cases).
- Era: years are counted as Anno Martyrum (A.M.), the Year of the Martyrs, beginning in AD 284 to commemorate the persecutions under Emperor Diocletian.
The 13 Coptic months in order: Tout, Baba, Hator, Kiahk, Toba, Amshir, Baramhat, Baramoda, Bashans, Paona, Epep, Mesra, Nasie.
How the conversion works
Both directions route through the Julian Day Number (JDN), a continuous count of astronomical days used as a universal intermediary. The Coptic epoch is fixed at JDN 1825030 = 1 Tout 1 A.M. Converting a Gregorian date to a JDN and then from JDN to Coptic — or the reverse — is fully deterministic. There is no accumulated drift or approximation: every date maps to exactly one date in the other calendar.
Example conversions
The Coptic New Year, 1 Tout, falls on 11 September in most Gregorian years — or 12 September in the year before a Coptic leap year. For example, 1 Tout 1741 A.M. corresponds to 11 September 2024.
Going the other direction: entering 25 December 2024 (Gregorian Christmas) returns 15 Kiahk 1741 A.M. — Kiahk is the month in which the Coptic Orthodox Church celebrates the main Advent/Christmas liturgical season, explaining why Coptic Christmas is observed on 7 January Gregorian (29 Kiahk or 28 Kiahk A.M.).
Practical uses
- Liturgical planning: finding the Gregorian date of a Coptic feast or fast.
- Historical research: reading Egyptian or Ethiopian documents dated in A.M. and converting to Gregorian to align with other sources.
- Ethiopian calendar: the Ethiopian calendar (Ge’ez calendar) shares the same structure and epoch, so conversions are closely related, though the tool is built specifically for the Coptic A.M. reckoning.
All calculation happens locally in your browser — nothing is ever sent anywhere.