About

Astrological compatibility analysis relies on the geometric relationships (aspects) between zodiac signs on the ecliptic, combined with elemental and modal classifications. A trine aspect (120° separation) between two signs indicates elemental harmony, while a square (90°) signals friction that can manifest as growth or conflict. This tool computes a composite compatibility score C by weighting four astrological factors: element affinity (35%), angular aspect (30%), modality interaction (20%), and polarity alignment (15%). Results are approximate models of traditional synastry. A full natal chart comparison requires exact birth times and planetary positions, which this sun-sign tool does not account for.

The category breakdown (Love, Communication, Trust, Values, Shared Activities) maps astrological sub-factors to relational domains. Fire - Air pairings tend to score high on Communication and Activities but lower on Trust stability. Earth - Water pairings often show strong Trust and Values alignment but may score lower on spontaneous activity compatibility. Note: conjunctions (0°) between identical signs produce high intensity scores but not necessarily high harmony. Same-sign pairings amplify both strengths and blind spots.

Formulas

The composite compatibility score C is computed as a weighted sum of four normalized sub-scores, each ranging from 0 to 1:

C = 100 × (0.35 ⋅ E + 0.30 ⋅ A + 0.20 ⋅ M + 0.15 ⋅ P)

Where E = element affinity score. Same element → 1.0. Complementary elements (Fire - Air, Earth - Water) → 0.8. Neutral (Fire - Earth, Air - Water) → 0.4. Opposing (Fire - Water, Earth - Air) → 0.2.

Where A = aspect angle score. The angular separation θ between two signs is calculated from their ecliptic positions:

θ = |pos₁ − pos₂|

Aspect scores: Conjunction (0°) → 0.7, Sextile (60°) → 0.85, Trine (120°) → 1.0, Square (90°) → 0.3, Opposition (180°) → 0.5, Quincunx (150°) → 0.2, Semi-sextile (30°) → 0.55.

Where M = modality interaction score. Same modality → 0.4 (tension). Cardinal - Fixed → 0.6. Cardinal - Mutable → 0.8. Fixed - Mutable → 0.9.

Where P = polarity alignment score. Same polarity (both Positive or both Negative) → 0.8. Opposite polarity → 0.5.

Category sub-scores (Love, Communication, Trust, Values, Activities) are derived by re-weighting these same four factors with domain-specific emphasis. For example, Love weights element affinity at 0.45 while Communication weights modality at 0.40.

Reference Data

Sign	Symbol	Dates	Element	Modality	Ruling Planet	Polarity	Position (°)
Aries	♈	Mar 21 - Apr 19	Fire	Cardinal	Mars	Positive	0
Taurus	♉	Apr 20 - May 20	Earth	Fixed	Venus	Negative	30
Gemini	♊	May 21 - Jun 20	Air	Mutable	Mercury	Positive	60
Cancer	♋	Jun 21 - Jul 22	Water	Cardinal	Moon	Negative	90
Leo	♌	Jul 23 - Aug 22	Fire	Fixed	Sun	Positive	120
Virgo	♍	Aug 23 - Sep 22	Earth	Mutable	Mercury	Negative	150
Libra	♎	Sep 23 - Oct 22	Air	Cardinal	Venus	Positive	180
Scorpio	♏	Oct 23 - Nov 21	Water	Fixed	Pluto	Negative	210
Sagittarius	♐	Nov 22 - Dec 21	Fire	Mutable	Jupiter	Positive	240
Capricorn	♑	Dec 22 - Jan 19	Earth	Cardinal	Saturn	Negative	270
Aquarius	♒	Jan 20 - Feb 18	Air	Fixed	Uranus	Positive	300
Pisces	♓	Feb 19 - Mar 20	Water	Mutable	Neptune	Negative	330

Frequently Asked Questions

Same-sign pairings form a conjunction aspect (0°), which scores 0.7 rather than 1.0. While element and polarity are identical (maximum scores), the modality sub-score for same modality is only 0.4 due to inherent tension when two signs share the same operating mode. Two Cardinal signs both want to lead; two Fixed signs both resist change. The composite score reflects this nuance.

Fire-Air pairings score highly on Communication (shared positive polarity, complementary expression styles) and Activities (mutual enthusiasm), but lower on Trust (Air's detachment can unsettle Fire's need for loyalty). Earth-Water pairings excel in Trust and Values (shared negative polarity, mutual need for security) but may score lower on Activities due to preference for routine over spontaneity.

A trine (120° separation) receives the maximum aspect score of 1.0, representing signs of the same element that naturally understand each other (e.g., Aries-Leo, both Fire). A sextile (60° separation) scores 0.85, representing signs of complementary elements (e.g., Aries-Gemini: Fire-Air) that require slightly more effort but still produce strong compatibility.

Traditional astrology acknowledges squares as catalysts for growth through friction. However, friction is not compatibility. The square aspect score of 0.3 reflects the challenge these pairings face in daily harmony. Growth potential exists but requires conscious effort. The tool measures natural compatibility, not developmental potential.

Sun-sign compatibility captures approximately 15-20% of the full synastry picture. A complete analysis requires Moon signs (emotional compatibility), Venus signs (love language), Mars signs (conflict style), and the aspects between all planetary placements in both charts. This tool provides a valid but limited framework. Two people with low sun-sign scores may have excellent Moon or Venus compatibility.

Partially. Opposite-polarity pairings (Positive-Negative) receive a polarity score of 0.5, reflecting the attraction-through-difference principle. However, the aspect angle for opposing signs (180°) scores 0.5, which captures the magnetic pull of opposition aspects. Together, these two factors model the classic "opposites attract" dynamic without overweighting it.