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Synastry Calculator — Relationship Compatibility

Compare two natal charts to discover relationship dynamics, strengths, and challenges.

Person A

Birth Date Birth Time Birth City

Person B

Birth Date Birth Time Birth City

What Is Synastry?

Synastry is the branch of astrology that compares two natal charts to analyze relationship dynamics. By overlaying one person's planets onto the other's chart, astrologers can identify areas of harmony, tension, attraction, and growth potential. Synastry goes far beyond Sun sign compatibility — it examines every planetary connection between two people for a complete relationship picture.

How Is It Calculated?

Synastry analysis compares every planet in Person A's chart with every planet in Person B's chart, calculating angular aspects (conjunction, sextile, square, trine, opposition) between them. Our engine also performs house overlay analysis — showing where one person's planets fall in the other person's houses. This reveals which life areas (career, home, romance, etc.) each person activates in the other.

Why Does It Matter?

Whether it's a new relationship or a decades-long partnership, synastry provides insight that goes beyond personality tests. It explains why some people feel magnetic while others feel challenging. Understanding synastry helps navigate differences with compassion, appreciate each partner's unique contribution, and recognize opportunities for growth in the relationship.

Frequently Asked Questions

What is a synastry chart?

A synastry chart overlays the natal charts of two people to analyze how their planets interact. By comparing all planetary positions, it reveals areas of attraction, harmony, tension, and growth potential in the relationship. Astro Engine's synastry calculator analyzes all inter-chart aspects and house overlays for a complete picture.

How accurate is astrological compatibility?

Sun sign compatibility is just a starting point — full synastry analysis comparing all planetary positions between charts is significantly more nuanced and deeper. Accuracy depends on correct birth data, especially time. Astrology describes relationship dynamics and potentials rather than making absolute predictions.

Is exact birth time needed for synastry?

Exact birth time significantly improves synastry accuracy, especially for house overlay analysis, Moon aspects, and Ascendant contacts. If birth time is unknown, analysis can still be done on planetary aspects in signs, but house positions and Ascendant interactions will be missing.

Can synastry predict if a relationship will work?

Synastry reveals dynamics and potential challenges, but no chart comparison can predict relationship success. Free will, communication, and commitment matter more than any aspect. Challenging aspects often indicate the most growth-oriented relationships.

What are the most important synastry aspects?

Venus-Mars aspects indicate romantic and physical chemistry. Moon-Moon and Moon-Venus aspects show emotional compatibility. Sun-Moon aspects reveal fundamental harmony between core identity and emotional needs.