Compatibility calculators usually present a percentage the way a magician presents a card: no method, no reasoning, just a number you are meant to feel something about. Ours shows its work. This page explains exactly how the scores on our 78 compatibility pages are produced — the element system underneath them, the base scores, the small variation that makes each pair unique, and the bands we use to describe the result. It also explains, plainly, what a sun-sign score cannot tell you, because an honest method includes its own limits.
Every sign belongs to one of four elements — Fire, Earth, Air, or Water — and classical astrology treats the relationships between elements as the first layer of compatibility. Two elements are natural allies: Fire and Air feed each other (air makes flame brighter; fire gives air direction and warmth), and Earth and Water nourish each other (water makes earth fertile; earth gives water banks and shape). Signs sharing an element understand each other's native language. The cross pairs — Fire with Earth or Water, Air with Earth or Water — are not doomed; they simply start with a translation gap, because their instincts about pace, conflict, and affection genuinely differ.
There are ten possible element combinations, and each carries a published base score on our scale: Air–Fire starts highest at 90; Water–Water and Earth–Water at 89; Air–Air at 88; Fire–Fire at 87; Earth–Earth at 86. The cross pairs start lower: Air–Water 68, Earth–Fire 66, Air–Earth 65, and Fire–Water 62. These numbers encode the classical view described above, nothing more occult than that. Two same-element pairs score in the high 80s rather than the 90s because sharing a language also means sharing a blind spot — two Fire signs egg on each other's excesses; two Earth signs can entrench each other's ruts.
If scores stopped at the element base, all twelve Fire–Water pairs would be identical, which would make for dull pages and a false impression of precision about individual signs. So each pair gets a small, deterministic adjustment: the two sign names are hashed (the same FNV-1a method our daily horoscopes use) and fed to a seeded generator, producing a variation between −5 and +5 points. The result is clamped between 45 and 97. "Deterministic" matters: the adjustment is not re-rolled per visitor, and it never changes. The Leo–Virgo score is the Leo–Virgo score, for everyone, forever, and anyone can reproduce it from the published code.
From the overall score, the same seeded stream derives three sub-scores — love, friendship, and work — each nudged a few points in its own direction and clamped between 40 and 99. This mirrors something true about real pairings: two signs can be excellent colleagues and exhausting roommates, or wonderful friends whose work styles collide. The sub-scores are variations on the pair's theme, not independent measurements, and we present them that way. Each compatibility page also carries a band label — Exceptional, Strong, Workable, or Challenging — with advice matched to the band, plus a section on the pair's characteristic challenge and its most reliable fix.
Here is the honest part. A sun-sign score is a summary of how two temperaments tend to interact — nothing more. It does not use birth charts, because this site never collects birth data; it cannot see the Moon signs, histories, values, or effort of two actual people; and it is not a verdict on any real relationship. Plenty of 65-percent pairings outlast 95-percent ones, because relationships run on communication and repair far more than on temperament. We publish the method precisely so you can hold the numbers at the right weight: a conversation starter, a lens for thinking about pace and language differences — entertainment with its workings showing. Used at that weight, we think it is genuinely useful. Try the checker and read your pair's challenge section first; in our experience, that is where the value is.