Zodiac Compatibility Calculator
Real compatibility is computed, not looked up: this calculator reads the actual cross-chart aspects between two birth charts and shows you the four scores with the reasoning behind them.
Some calculators show everyone the same 80%. Ours computes cross-chart aspects — change either birthday by a day and watch the numbers move.
Computed in your browser · Same engine as the full birth chart reading
PERSON A
PERSON B
What synastry is, and how this compatibility calculator scores it
Two birth charts. Twenty planets. One hundred angles measured between them. That is the arithmetic that runs before this compatibility calculator prints a single number. A synastry aspect is nothing more mysterious than an angle: take one person's Venus, take the other person's Moon, measure the degrees between them around the ecliptic. If that separation lands near 0°, 60°, 90°, 120° or 180°, the two bodies are in aspect. Each aspect carries a working orb, meaning how far off exact it may sit and still count: 8° for a conjunction, 4° for a sextile, 6° for a square, 7° for a trine, 8° for an opposition. Only the closest match per pairing is kept, and of the hundred pairings tested, most fall outside every orb and contribute nothing at all.
The four bars come out of that geometry by a recipe you could check line by line. Every surviving aspect is scored three ways: quality (a trine counts +1, a sextile +0.8, a conjunction +0.6, while a square counts as −0.7 and an opposition −0.5), tightness (an aspect a third of a degree off exact carries nearly its full value; one sitting at the edge of its orb carries almost none), and the standing of the two planets involved. Love weights Venus heaviest at 3, then the Moon at 2.5, Mars at 2, the Sun at 1.5. Work rearranges the furniture: Saturn 2.5, Mercury and Mars at 2. Friendship leads with Mercury. Both planets' weights are added together, so a Venus-to-Moon contact carries more into the Love score than any other single pair of bodies can. Overall alone earns a further bonus for element affinity between the two Suns and the two Moons, same element counting most, complementary next, everything else against. Swap Person A and Person B and nothing moves; the compatibility calculator is symmetric by construction.
That is the whole difference between this and a sun-sign percentage, which is not a computation at all. A Leo-with-Scorpio table holds 144 cells, written once, by a person, and every Leo and Scorpio who ever reads it gets the same cell forever. Nothing was measured. Run two different Leo and Scorpio couples through this compatibility calculator and the numbers separate, because the skies over their two mornings were not the same. Move either birthday by one day and watch the bars shift. The limits belong in the same breath. Those weights are a house recipe, defensible but not revealed truth, and the scale stops deliberately short of 0 and of 100 because no two charts earn either. A low Work score classically marks friction worth naming out loud. It is not a verdict.
Compatibility questions, honestly answered
How are the compatibility scores computed?
Both charts are cast from real ephemeris data, then every cross-chart aspect — one person's planets against the other's — is weighted by planet relevance (Venus and the Moon matter more for Love; Saturn and Mercury for Work), aspect quality and tightness. The four scores summarize that geometry. The AI summary then explains which specific aspects drove your numbers.
Is this the same for everyone with my sign?
No — that's the point. Sun-sign compatibility tables give all Leo-Scorpio pairs one verdict. This calculator uses full birth charts, so two different Leo-Scorpio couples get different scores because their skies differ.
Do we need birth times?
Scores compute fine without them — planets don't need a birth time. Times add rising-sign nuance. If one is missing, that person gets a noon chart and we say so.
Can a low score doom a relationship?
No, and we'd say so even if it were bad for business. Astrology is a reflective tradition, not a verdict. A low score names frictions worth talking about; plenty of durable pairs run on well-managed squares.
Is it free?
Yes — scores and the AI summary, no signup, no email. Fair-use limits keep it healthy.
Whose data is stored?
Neither person's. Charts are computed in your browser; birth data goes to the server only to write the summary and is not saved.