Synastry chart calculator
Compare two birth charts planet by planet: attraction, ease and friction, measured to the degree. The classic astrology compatibility method.
Save both people and the comparison appears below.
How aspects work
An aspect is just the angle between two planets along the zodiac. Certain angles (fractions of the circle) are read as meaningful, each with an “orb”, a margin of a few degrees. Move your Venus and their Mars.
Trine (120°), orb 0.0°
natural flow; talents that come easily (sometimes too easily to notice).
How to read synastry
Each row in the table is one of your planets in aspect to one of theirs. Read it as a sentence: “my Moon trines your Venus” means your emotional needs and their way of loving fit naturally. Tighter orbs are stronger. Personal planets (Sun, Moon, Mercury, Venus, Mars) and the Ascendant carry most weight; aspects to Uranus, Neptune and Pluto are shared by everyone born within a few years, so they count less.
The harmony and friction numbers are a quick weighted tally, not a verdict. Two high numbers usually mean a strong, eventful bond; two low numbers, a lighter connection. For the relationship as a single entity, try the composite chart.
Questions people ask
What is a synastry chart?
Synastry compares two birth charts by overlaying them and measuring the angles (aspects) between one person’s planets and the other’s. It’s the most detailed form of astrological compatibility, far beyond comparing Sun signs.
Which synastry aspects matter most?
Traditionally: Sun–Moon, Moon–Moon and Venus–Mars contacts for attraction and emotional fit, Venus–Saturn and Sun–Saturn for commitment and staying power, and anything touching the other person’s Ascendant. Tight orbs (under 3°) are felt most.
Do we both need birth times?
Not for planet-to-planet aspects. Times add Ascendant contacts and house overlays, and pin down a fast-moving Moon. Without a time we use noon.
What is the difference between synastry and a composite chart?
Synastry looks at how two separate people affect each other. A composite chart blends both into a single chart for the relationship itself, using the midpoints of each pair of planets.
Are hard aspects bad in synastry?
No. Squares and oppositions bring friction but also chemistry and growth; many long relationships have plenty. A chart with only easy aspects can feel comfortable but flat.