Dictionary term
Intercalation
Direct answer
Intercalation is the insertion of an extra day, month, or other interval to keep a calendar aligned with its astronomical or seasonal target.
Intercalation adds calendar time to correct accumulated drift.
Intercalation adds calendar time to correct accumulated drift.
A cycle or timeline schematic for comparing the named timekeeping concept.Quick reference
- Use when
- Use Intercalation when explaining leap days, leap months, embolismic years, and calendar reform.
- Do not use it for
- Do not assume every intercalation rule follows the Gregorian four-year pattern.
- Reference category
- Calendars & Timekeeping
- Related terms
- Week Number, Intercalary Day, Calendar, Julian Date
The Chapter · Mystery School
Learn to read the sky for yourself
A mystery school of astrology with a worldwide chapter: letters on the chart and the soul, readings under one sky, and a rule of honesty about what the stars can and cannot say.
- The founding letter, with what the school studies and how it meets
- First word each season, when the doors open
- A seat at the gatherings, wherever in the world you are
Reading about Intercalation? The chapter is where readers like you meet.
Founding circle · forming now
The list costs nothing. Word of the school and its gatherings, nothing else. Unsubscribe at any time.
The story behind Intercalation
Ancient administrators and astronomer-priests used observation or fixed cycles to decide when an extra interval was required.
Intercalation in spiritual tradition
Spiritually, intercalation is a practical reminder that human systems sometimes need correction to remain aligned with reality.
Intercalation: fact and faith, kept distinct
This is a factual calendar, astronomy, Earth-science, cultural-history, or observational reference. It can support wonder and practical planning without becoming a claim of fate, spiritual causation, or private revelation.
Intercalation in numerology
Intercalation is not a numerology claim. Any numbers attached to it should retain their ordinary scientific, calendrical, navigational, or historical meaning unless a separate symbolic interpretation is clearly labeled.
Why Intercalation matters
Without intercalation, calendars based on incommensurable lunar months, solar years, and whole days gradually move away from their intended season or phase.
Intercalation at work: an example
Gregorian intercalation adds February 29 in most years divisible by four, with century exceptions.
Where interpretation stops
Intercalation is presented as sourced astronomy, calendrical, Earth-science, cultural, or instrument-history reference. Definitions should distinguish measured phenomena from civil convention and historical interpretation, preserve location and time dependencies, and avoid turning factual sky data into a deterministic personal claim.
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
- Also appears in
- Calendars & Timekeeping
- Aliases
- None listed
- Last updated
- 2026-07-16
Find the calendar correction rule
Intercalation in a book is one thing; Intercalation in your own birth chart is your life. The Oracle casts your real chart and tells you what it means for your love, your work, and your year ahead, in conversation, free.
Speak with the OracleRelated terms
More in Calendars & Timekeeping
- Local Apparent Solar Time
- Old Style Date
- Universal Time
- Astronomical Day
- Callippic Cycle
- Draconic Month
- Geocentric Coordinate Time
Common questions
What is Intercalation?
Intercalation is the insertion of an extra day, month, or other interval to keep a calendar aligned with its astronomical or seasonal target.
How is Intercalation used in an almanac?
Use Intercalation when explaining leap days, leap months, embolismic years, and calendar reform.
What should I avoid when interpreting Intercalation?
Do not assume every intercalation rule follows the Gregorian four-year pattern.
