About

The Celtic Tree Zodiac derives from the Ogham alphabet, a system of 13 lunar months each governed by a sacred tree. Unlike the Gregorian solar calendar with 12 signs, the Druidic system divides the year into 13 periods of roughly 28 days, aligned to the lunar cycle. Each tree carries specific elemental associations, ruling planets, and character archetypes documented in medieval Irish manuscripts. Misidentifying your tree sign is common because several trees span a year boundary (Birch runs Dec 24 - Jan 20), and online sources frequently disagree on exact cutoff dates. This calculator uses the Beth-Luis-Nion ordering, the most widely accepted scholarly arrangement, with dates cross-referenced against the White Goddess calendar framework by Robert Graves (1948).

Note: the Celtic Tree Calendar is a modern reconstruction. No surviving Druidic text explicitly maps trees to birthdate personality. The system approximates a tradition filtered through 19th- and 20th-century Celtic revivalism. Treat results as cultural exploration, not psychological diagnosis.

Formulas

The Celtic Tree Zodiac maps each birthdate to one of 13 lunar periods. The matching algorithm normalizes any date to a day-index:

D = month × 100 + day

where D is a sortable integer representing the calendar position. Each tree sign defines a range [D_start, D_end]. For signs that cross the year boundary (e.g., Birch: Dec 24 - Jan 20), two sub-ranges are stored:

D ≥ 1224 or D ≤ 120

The algorithm iterates through all 13 tree records and returns the first match. Leap year dates (Feb 29) are accepted and fall within the Ash period. No astronomical ephemeris is required because the system is calendar-based, not sidereal.

where month = month number (1 - 12), day = day of month (1 - 31).

Reference Data

Tree	Ogham	Dates	Planet	Element	Key Trait	Animal	Color	Gemstone	Compatible
Birch (Beth)	ᚅ	Dec 24 - Jan 20	Sun	Earth & Air	Ambition	White Stag	White	Rock Crystal	Vine, Willow
Rowan (Luis)	ᚆ	Jan 21 - Feb 17	Uranus	Fire & Earth	Vision	Crane	Red / Grey	Peridot	Ivy, Hawthorn
Ash (Nion)	ᚇ	Feb 18 - Mar 17	Neptune	Water & Fire	Intuition	Seal / Seahorse	Pale Green	Coral	Willow, Reed
Alder (Fearn)	ᚈ	Mar 18 - Apr 14	Mars	Fire & Water	Courage	Fox	Crimson	Ruby	Oak, Birch
Willow (Saille)	ᚅ	Apr 15 - May 12	Moon	Water	Resilience	Hare	Silver	Moonstone	Birch, Ash
Hawthorn (Huath)	ᚅ	May 13 - Jun 9	Vulcan	Fire & Air	Contradiction	Owl	Purple	Lapis Lazuli	Rowan, Ash
Oak (Duir)	ᚉ	Jun 10 - Jul 7	Jupiter	Earth	Strength	Wren	Black / Dark Brown	Diamond	Alder, Reed
Holly (Tinne)	ᚊ	Jul 8 - Aug 4	Earth	Fire & Earth	Nobility	Horse	Dark Grey	Bloodstone	Elder, Ash
Hazel (Coll)	ᚋ	Aug 5 - Sep 1	Mercury	Air	Wisdom	Salmon	Brown / Orange	Amethyst	Rowan, Hawthorn
Vine (Muin)	ᚌ	Sep 2 - Sep 29	Venus	Water & Earth	Refinement	Swan	Pastel Blue	Emerald	Birch, Willow
Ivy (Gort)	ᚍ	Sep 30 - Oct 27	Persephone	Water & Air	Tenacity	Butterfly	Blue	Opal	Rowan, Oak
Reed (Ngetal)	ᚎ	Oct 28 - Nov 24	Pluto	Water & Fire	Investigation	Hound	Orange / Reed-Gold	Jasper	Ash, Oak
Elder (Ruis)	ᚏ	Nov 25 - Dec 23	Saturn	Air & Fire	Transformation	Raven	Dark Red / Black	Jet	Holly, Alder

Frequently Asked Questions

The system is lunar, not solar. A lunar month averages approximately 29.53 days, yielding roughly 13 full cycles in a 365.25-day solar year. The Gregorian zodiac uses 12 signs because it divides the ecliptic into 30° sectors. The Celtic model instead tracks the Moon's rhythm, which is why each tree period lasts approximately 28 days.

It is primarily a modern reconstruction. Robert Graves proposed the Beth-Luis-Nion tree alphabet sequence in The White Goddess (1948). While the Ogham alphabet and tree associations are genuinely attested in medieval Irish sources (the Auraicept na n-Éces, c. 7th century), no surviving Druidic manuscript maps trees to personality traits or birthdates. The zodiac framework was layered on by 20th-century neo-Celtic movements.

February 29 falls within the Ash (Nion) period, which runs Feb 18 - Mar 17. The calculator accepts leap dates without error. Your tree sign, traits, and associations are identical to anyone born between those dates.

Birch spans Dec 24 - Jan 20, crossing the calendar year. The algorithm stores two sub-ranges for such signs: D ≥ 1224 (December portion) and D ≤ 120 (January portion). A birthdate matching either sub-range is assigned Birch. This prevents the common bug where cross-year signs return no match.

Compatibility pairings in Celtic tree astrology are derived from elemental affinity (Water trees pair well with Earth trees) and from Ogham kenning relationships documented in the Scholar's Primer. They are interpretive, not prescriptive. No ancient source provides a compatibility matrix. Treat them as thematic resonance, not relationship guarantees.

Three competing Ogham orderings exist: Beth-Luis-Nion (Graves), Beth-Luis-Fearn (manuscript order), and various neo-Druidic variants. Each shifts date boundaries by several days. This calculator uses Beth-Luis-Nion, the most commonly cited in English-language Celtic astrology sources. If another site disagrees by 1 - 3 days, they likely follow a different ordering or have adjusted for a different lunar epoch.