Synastry Calculator
Enter two birth charts to see how your planets interact... no account needed.
About Synastry
What is synastry?
Synastry is the astrology of relationships. It compares two birth charts to identify aspects — angular relationships — between one person's planets and another's. These aspects reveal attraction, friction, communication patterns, and growth potential between two people.
What aspects does the synastry calculator look for?
The calculator checks for the five major aspects between all personal and social planets: conjunction (0°), sextile (60°), square (90°), trine (120°), and opposition (180°). Harmonious aspects (conjunction, trine, sextile) tend to create ease and flow. Tense aspects (square, opposition) create friction and growth edges.
Do I need birth time for synastry?
Birth time improves accuracy — especially for Moon placement (which moves every 2–2.5 days) and house positions. But even without exact times, a synastry reading of Sun, Mercury, Venus, Mars, Jupiter, and Saturn placements gives meaningful insight into the relationship dynamic.
What is the most important aspect in synastry?
Sun–Moon aspects are often considered the most important indicator of compatibility. Venus–Mars aspects reveal romantic and physical attraction. Sun–Venus shows appreciation and admiration. Moon–Moon aspects show emotional attunement. No single aspect tells the whole story.