Calendars and time
Epact
Direct answer
Epact: The Epact is a calendar number representing the Moon approximate age at a reference date, used especially in ecclesiastical lunar calculations.
The Epact is a computus value used to track the calendar Moon age.
$0 today, then $12/month after 7 days. Cancel anytime.
At a glance
- Found in
- Calendars & Timekeeping
- Related
- Intercalary Month, Golden Number, Calendar, Julian Date
The Epact is a computus value used to track the calendar Moon age.
A cycle or timeline schematic for comparing the named timekeeping concept.
What does your own chart say about you?
Choose love, work or purpose. Your reading is written from your chart. Your reading uses your own birth details.
Walk through Alex’s whole example first
The Road of AgesSee the turning points of your whole life, from your birth date
See your road's shape
Prefer to explore first?
The Road of AgesThe turning points of your whole life, from your own chart
Walk my road
Free, by email
Your daily Almanac letter
One short letter at 7 each morning: the day’s theme read for your own chart, and one thing to do with it.
The story behind Epact
Medieval and Gregorian computists refined epact tables to reconcile lunar cycles with changing solar calendar rules.
Why Epact matters
Epacts help coordinate lunar phase tables with solar calendar dates when calculating moveable feasts.
Epact in practice: an example
An annual epact can guide a table to the ecclesiastical full moon used in an Easter calculation.
Where readings of Epact go wrong
A common error is to treat an epact as a direct modern observation of the Moon exact illuminated phase.
Sources and editorial method
Research references used for this entry include:
- U.S. Naval Observatory: Introduction to Calendars - Official overview of calendar systems, leap rules, eras, and historical calendar reform.
- Source
- The Great Almanac Dictionary
- Category
- Calendars & Timekeeping
- Last updated
- 2026-09-26
Read the computus table
A definition tells you what it is; your own birth chart tells you what it means for you. The Oracle casts your real chart and answers for your love, your work, and your year ahead, in conversation. It opens with the 7-day Seeker trial.
Speak with the OracleRelated terms
More in Calendars & Timekeeping
From the reference page to your own chart
Every word here
is in your own chart.
- A personal reading about love, work or purpose, written from your chart
- A practical next step to consider
- It opens with 7 days free, with the AI Oracle and daily guidance
$0 today, then $12/month after 7 days. Cancel anytime.
Common questions
What is the Epact?
The Epact is a calendar number representing the Moon approximate age at a reference date, used especially in ecclesiastical lunar calculations.
What do people get wrong about the Epact?
A common error is to treat an epact as a direct modern observation of the Moon exact illuminated phase.
Free, by email
The Almanac, in your inbox at 7
One short letter at 7 each morning: the day’s theme read for your own chart, and one thing to do with it.
