Free Synastry Chart Calculator
Overlay two birth charts and get a free written interpretation in about a minute — Tropical, True Sidereal, and Draconic in one result. Tell us who they are — partner, parent, friend, coworker — and it reads the right way for the relationship you actually have.
What is synastry?
Synastry overlays two birth charts to map the dynamics between two people. Each person's planets form aspects with the other's — conjunctions, squares, trines — revealing what each person activates in the other.
Synthesis runs synastry in both Tropical and True Sidereal systems, then layers numerology and Chinese zodiac as weighted inputs. Multiple instruments, one connection. The goal isn't to score compatibility — it's to identify the dominant relational pattern.
What makes this reading different
Toned for the relationship you actually have
Every reading is shaped by who they are to you and what you want to understand. A reading for your mother reads nothing like one for a new partner. Pick the relationship type, the questions you care about, and add a personal note — the AI uses all three to set tone, focus, and register.
Every chart claim is fact-checked
Aspects, orbs, degrees, geometric patterns, and stellium claims are automatically verified against the actual computed chart before delivery. Invented aspects get softened. Fabricated scenarios — clock times, brand names, weekday inventions — get stripped. The reading you receive only asserts what the placements actually support.
Synastry readings are generated by artificial intelligence for entertainment and self-reflection purposes only. They are not a substitute for professional relationship counseling.
Major synastry aspects, explained
A synastry chart lays one person's planets over another's and studies the angles they form. A handful of contacts carry most of the story. None of them decides a relationship on its own — read them as recurring patterns and tendencies, never verdicts. What you do with the energy is always yours.
Sun–Moon: the sense of being understood
When one person's Sun touches the other's Moon — especially by conjunction, trine, or sextile — there is often an easy sense of being seen and cared for. The Sun person tends to feel recognized; the Moon person tends to feel emotionally safe. Squares and oppositions here don't cancel the bond; they usually mark where warmth and routine have to be negotiated rather than assumed.
Venus–Mars: attraction and chemistry
Venus and Mars contacts between two charts are the classic markers of physical and romantic pull. A Venus–Mars conjunction or opposition often shows up as strong chemistry, while a square can read as friction that still crackles with desire. Chemistry is an invitation, not an obligation — these aspects describe the spark, not what you choose to build with it.
Moon–Moon: emotional rhythm
Moon-to-Moon contacts describe how two people's inner weather lines up. Harmonious Moon aspects tend to mean you reassure each other without much translation. Challenging ones point to different emotional languages — not incompatibility, but a place where naming what you each need does more work than assuming the other already knows.
Saturn overlays: commitment and weight
Saturn contacts are the staying-power aspects. Saturn touching a partner's Sun, Moon, or Venus can feel steadying and serious, and it often appears in long-lasting bonds. The same contact can feel heavy when it tips into caution or control. Saturn tends to reward relationships built deliberately over time rather than rushed.
Ascendant and house overlays: where you meet
Beyond aspects, synastry looks at which of your houses a partner's planets fall into — the area of life they light up. A planet in your first house colors how you see yourself around them; the fifth leans toward romance and play; the seventh feels like classic partnership; the eighth runs deep and transformative; the tenth touches your public life and direction. House overlays show where a connection tends to be felt most, not whether it is meant to be.
How to read a synastry chart
Reading synastry is less about scoring a match and more about noticing patterns. A workable order:
- 1
Start with the luminaries. Look at Sun and Moon contacts first — they set the baseline tone of understanding and emotional fit.
- 2
Add Venus and Mars. These color attraction, affection, and how the two of you move toward each other.
- 3
Weigh Saturn and the outer planets. Saturn shows durability and responsibility; Jupiter shows ease and growth; the outer planets add intensity or unpredictability.
- 4
Place the overlays. See which houses each person's planets fall into to understand where the relationship lives day to day. Read the whole picture — one hard aspect rarely outweighs a chart full of support, and one easy aspect rarely carries a relationship alone.
Sidereal compatibility: True Sidereal and Draconic synastry
Because True Sidereal placements sit roughly 31 degrees from their tropical counterparts, the same two charts can produce different contacts in each system. A tropical Venus–Mars trine might read as a square in sidereal. That isn't a contradiction — the tropical layer often describes the relationship you consciously experience, while the sidereal layer can point to the deeper draw underneath.
Reading both side by side is why a bond can feel smooth on the surface and complicated underneath, or the reverse. Synthesis compares both systems in one report rather than forcing you to choose.
For the layer beneath the everyday personality overlay — the soul-level pull some couples describe — compare each chart's draconic positions with Draconic Synastry.
Throughout, treat every aspect as a tendency you can work with, not an outcome handed down. Synastry describes the terrain; how you travel it stays with the two of you.
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Questions
What is a synastry chart?
A synastry chart overlays two birth charts to analyze relationship dynamics. It shows how one person's planets aspect another's, revealing areas of harmony, tension, and growth between two people.
How is synastry different from a composite chart?
Synastry compares two separate charts side by side, showing how each person affects the other. A composite chart merges both charts into one, representing the relationship itself as its own entity.
Do I need an exact birth time for synastry?
Birth time improves accuracy — especially for Rising sign and house placements. Without it, the core planet-to-planet aspects (Sun, Moon, Venus, Mars) are still meaningful.
What systems does Synthesis use for synastry?
Synthesis calculates synastry in both Tropical and True Sidereal systems, then layers numerology and Chinese zodiac as weighted inputs. Multiple instruments, one connection.
How does Synthesis compare to other synastry calculators?
Most free synastry calculators show one zodiac system (usually Tropical) and a single 'compatibility score'. Synthesis computes synastry in Tropical and True Sidereal at the same time, scores the connection across four dimensions (overall, romantic, communication, stability), and frames the analysis as a pattern of tendency rather than a forecast. The free overview shows the cross-chart aspects; a paid reading ($28 one-time) provides a written multi-system analysis.
Is Synthesis synastry free?
The synastry overview — cross-chart aspect grid, four-dimension scores in both Tropical and Sidereal — is free. The full written synastry reading is $28 one-time and includes a PDF analysis grounded in pattern language, not prediction.
Is the synastry chart interpretation free?
Yes. The free result includes a written snapshot interpretation plus the full cross-aspect grid and compatibility scores across Tropical, True Sidereal, and Draconic overlays — no payment required. The optional $28 reading goes deeper with a long-form five-system analysis and PDF.
How do you prevent AI hallucinations in the reading?
Every chart claim — aspects, orbs, degrees, geometric patterns (Yods, T-squares, Grand Trines), stelliums — is automatically verified against the actual computed chart before delivery. Claims that don't match get corrected or softened. A separate post-pass strips the common AI failure modes: fabricated specific scenarios, made-up clock times, invented brand names, weekday inventions. The reading you receive is grounded in your actual chart, not the AI's imagination.