Compatibility Calculator

Overview

Compatibility tables are generated from a small set of rules about elements, modalities and the angular distance between signs. This page documents those rules so any published table can be checked, and states what the evidence shows.

• Sign-pair compatibility follows mechanically from element and angular relationship — no ephemeris is involved.
• The whole scheme depends only on two birth dates reduced to Sun signs.
• The tradition's own method is full-chart synastry, not sign matching.
• Studies using large relationship datasets have found no sign-based effect.

The rules that generate a table

• Signs of the same element (120 degrees apart, forming a trine) — traditionally read as harmonious.
• Fire with air, and earth with water (60 degrees apart, a sextile) — traditionally read as complementary.
• Signs 90 degrees apart (a square) — traditionally read as friction.
• Signs 180 degrees apart (an opposition) — traditionally read as polarity or complementary tension.
• Adjacent signs, 30 degrees apart (a semisextile) — traditionally read as having little in common.
• Two people of the same sign (0 degrees, a conjunction) — traditionally read as mutual recognition that can tip into reinforcing a shared weakness.
• Signs 150 degrees apart (a quincunx, or inconjunct) — traditionally read as mismatched, sharing neither element, modality nor polarity.
• Applying these seven rules to all 78 unordered sign pairs reproduces essentially any published compatibility table.

Why the tables all look the same

Because they are generated from the same rules. Once the element and modality scheme is fixed, the angular relationship between any two signs follows automatically, and so does the traditional reading — seven rules exhaust all 78 pairs. There is no additional information in one compatibility chart compared with another.

This is worth knowing when evaluating any site that presents such a table as a result. It is a lookup produced by five rules, not a calculation over data — and it uses only the Sun's sign, discarding every other placement.

What the tradition actually prescribes

Traditional astrological practice compares complete charts. Synastry examines aspects between one person's planets and the other's, house overlays showing where each person's planets fall in the other's chart, and the relationship between the two Ascendants. Composite and Davison charts add further constructions.

Sun-sign compatibility is a twentieth-century popular simplification, and practitioners within the tradition are often its sharpest critics. Presenting it as what astrology says misrepresents the tradition as well as overstating the claim.

The evidence

Large-scale analyses of marriage and relationship records have tested for correlations between partners' sun signs and relationship formation or duration, and found nothing distinguishable from chance. The datasets used were large enough that an effect of the size popular compatibility claims imply would have been detectable.

Asteria Star documents how the tables are built and states that finding alongside them. The material is presented as a description of a tradition, not as guidance for decisions about relationships.

Continue in the data

Catalogues, hubs, and reference pages that hold the underlying records for this topic.

• CompatibilityThe tradition and its limitations.
• SynastryThe full-chart method.
• AspectsThe angular relationships behind the rules.

Frequently asked

How are zodiac compatibility tables generated?

From a handful of rules about the angular distance between signs: same element and 120 degrees apart is read as harmonious, 60 degrees as complementary, 90 as friction, 180 as polarity, 30 as having little in common, 150 as mismatched, and 0 — the same sign — as mutual recognition. Applying those seven to all 78 sign pairs reproduces essentially any published table. No ephemeris or chart data is involved.

Is sun-sign compatibility what astrologers actually use?

No. The tradition's own method is synastry — comparing two complete charts through inter-chart aspects, house overlays and the relationship between the Ascendants. Sun-sign matching is a twentieth-century popular simplification, and practitioners within the tradition are frequently its sharpest critics.

Is there evidence for astrological compatibility?

No. Large analyses of marriage and relationship records have looked for correlations between partners' sun signs and relationship formation or duration and found nothing beyond chance. The samples were large enough that an effect of the claimed magnitude would have been visible.