Synastry Calculator
Full synastry chart comparison for relationship astrology.
Synastry: Reading Two Charts Together
Synastry is the branch of astrology that compares two birth charts side by side to reveal the dynamics, chemistry, and challenges in a relationship. Where a single birth chart describes an individual, synastry describes the space between two people — how their planetary energies interact, amplify, or tension each other. Every significant relationship in your life has a synastry signature, whether romantic, familial, or professional.
How Synastry Works
In a synastry reading, each planet from one person's chart is overlaid onto the other's. The angular relationships (aspects) formed between the two charts — conjunctions, trines, squares, oppositions, and sextiles — describe the quality of interaction between those two planetary principles. A conjunction between Person A's Venus and Person B's Mars is one of the most classic romantic attraction signatures in synastry: Venus brings affection and beauty; Mars brings desire and initiative. When they meet in the same degree, the attraction tends to be immediate and magnetic.
House Overlays
Beyond inter-chart aspects, synastry also examines house overlays: which house does Person A's Sun fall in when placed on Person B's chart? If A's Sun falls in B's 7th house, A may feel like a natural partner or mirror for B — B sees A as representing what they seek in a committed relationship. If A's Sun falls in B's 12th house, the relationship may feel karmic, hidden, or spiritually significant, but potentially also hard to define or sustain in ordinary reality. House overlays describe the area of life that each person activates for the other.
The Most Important Synastry Contacts
Not all inter-chart aspects carry equal weight. The highest-priority contacts are: Sun–Moon aspects (especially conjunction and trine — the classic 'soul mate' signature of mutual recognition), Venus–Mars inter-aspects (attraction and sexual chemistry), Saturn contacts to personal planets (Saturn adds commitment and longevity, but also restriction and lessons — Saturn contacts often describe relationships that feel fated or karmic), and North Node contacts (when one person's planets conjunct the other's North Node, there is a strong sense of being cosmically drawn together in service of growth). Moon–Moon and Moon–Venus aspects describe emotional attunement and ease of nurturing each other.
Synastry vs Composite Chart
Synastry and composite charts answer different questions. Synastry shows how two individuals interact — the push and pull between their separate natures. The composite chart, calculated by finding the midpoint between each pair of corresponding planets, describes the relationship itself as an entity — its purpose, identity, and character as a third thing created by the union. Strong synastry with a weak composite can mean two people are intensely drawn together but struggle to build a stable shared life. Strong composite with mediocre synastry can mean the relationship is durable and purposeful even if the initial spark is quieter.