Compatibility Score
Definition
A compatibility score is a single number meant to sum up a relationship, built from a synastry comparison by giving each cross-chart aspect a point value and adding them up. The usual approach counts flowing aspects as positive, hard aspects as negative or as it-depends, conjunctions according to how naturally the two planets get along, and contacts between personal planets more heavily than ones between the slow outer planets. How it is actually done varies a lot from one app or system to the next — there is no agreed formula in the professional literature.
In Tradition
Modern Western relationship astrologers are cautious about compatibility scoring. They treat it as a quick way to get oriented, while accepting that it flattens a many-sided comparison into one number. The Greene–Forrest–Tompkins line stresses that you can't reliably add up the quality and tightness of individual aspects, the condition of each contacted planet, and where each person is in their own life. A score is best read as a rough first impression, not a verdict on the relationship.
In Practice
In practice, the automated compatibility scores that consumer astrology apps produce are most useful for sorting through many possible pairings, or for getting your bearings before deeper work. Professional astrologers usually start from the cross-aspect grid itself rather than the score, weigh Sun-Moon and Venus-Mars contacts by hand, and read the balance of elements and modes, the house overlays, and the chart-ruler patterns alongside the grid. A high or low score is treated as a reason to look more closely, not as a conclusion.
Historical Origin
Compatibility scoring is a 20th-century Western development of the computer era, with no classical forerunner. The Hellenistic and Arabic literatures compare two charts in words, not numbers — Ptolemy's Tetrabiblos IV.5 weighs friendship and enmity without adding anything up. Modern scoring schemes spread through late-20th-century synastry software and consumer products; that the technique has no single standard reference text reflects its informal status.
Etymology
Origin: English. Meaning: From Latin compatibilis (able to exist together) + Medieval Latin scorare (to notch, tally).
Further Reading
- Sue Tompkins, Aspects in Astrology
- Liz Greene, Relating: An Astrological Guide to Living with Others on a Small Planet