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Synastry calculator: compare two birth charts
Synastry compares two birth charts planet by planet. Enter two people's birth details to see every cross-chart aspect within orb, a plain-language note for the closest ones, and both people's Sun and Moon signs in the tropical and sidereal zodiacs. It works for any relationship. Nothing is stored or sent.
How does this synastry calculator work?
Each person's Sun through Pluto and the mean North Node (Rahu) are compared with every point in the other chart, plus the ascendant when a birth time is given. Aspects: conjunction 0°, sextile 60°, square 90°, trine 120° and opposition 180°. Orb: 8° when the Sun or Moon is involved, 6° otherwise. Key aspects are ranked by the planets involved and by how exact the angle is.
Both lenses use the same angles. A Venus–Moon trine is a trine whether you read it in the tropical or the Lahiri sidereal zodiac, because both zodiacs shift every planet by the same offset. What changes is the sign each planet sits in, so the tool shows both sets of sign pairs. Vedic compatibility matching (Ashtakoota or guna milan) is a separate scoring system that this preview does not compute.
Sun-sign pairs are a starting point; see the compatibility chart for all 78 pairs. For each person on their own, use the birth chart calculator or the big three calculator.
How we calculate
Is astrology a guarantee of what will happen?
No. These calculations locate celestial bodies; astrology is a reflection and timing tradition, not evidence of guaranteed health, financial or relationship outcomes.
How are these results calculated?
Positions come from Astronomy Engine, an open-source astronomy library, and are checked against Swiss Ephemeris in our methodology tests. Western readings use the tropical zodiac; Vedic readings subtract the Lahiri ayanamsa. Terms are defined in the glossary.
Next: compare your birth chart, see today's sky, or make a private vision board.