Enter both birth details for a detailed compatibility report based on real planetary positions — not just sun signs.
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A synastry compatibility calculator is an astrological tool that compares two people's birth charts to reveal the dynamics of their relationship. Unlike simple zodiac sign compatibility — which only considers your sun sign — synastry analyses the exact positions of all planets at the moment each person was born, then maps how those planetary energies interact.
The word "synastry" comes from the Greek syn (together) and astron (star). In practice, a synastry chart overlays one person's natal chart onto the other's, calculating the angular relationships (aspects) between every pair of planets. These aspects reveal areas of natural harmony, magnetic attraction, communication patterns, and potential friction — giving you a detailed map of your relationship's cosmic blueprint.
Our free compatibility calculator uses the astronomy-engine library for precise planetary position calculations based on your exact birth date, time, and location. The result is a comprehensive love compatibility report with dimensional scores, aspect-by-aspect interpretations, and actionable relationship insights — far beyond what any sun sign comparison can provide.
Input the birth date, time, and location for both people. Exact birth time gives the most accurate results, but the calculator works with approximate times too.
Our engine computes the exact position of Sun, Moon, Mercury, Venus, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto for both charts using astronomical algorithms.
Receive a detailed compatibility report with 5-dimensional scores, a natural language analysis of your strengths and growth areas, and a full planetary aspect table.
Every report includes five key sections designed to give you a complete picture of your relationship dynamics.
Scores across Emotional, Communication, Romantic, Passion, and Growth dimensions — displayed as a radar chart for instant visual understanding.
Every significant aspect between your planets is identified and interpreted — conjunctions, trines, squares, oppositions, sextiles, and quincunxes.
Your harmonious aspects are grouped as strengths, and challenging aspects are framed as growth opportunities — with practical advice for each.
Each aspect comes with a human-readable interpretation explaining what it means for your specific relationship — not generic astrology jargon.
A complete technical reference showing every planetary aspect, the exact orb (degree of precision), and aspect type — for those who want the raw data.
Upgrade to Pro for outer planet aspects (Jupiter through Pluto), house overlay analysis, 270+ detailed interpretations, and downloadable PDF reports.
Your overall compatibility score is calculated by analysing the aspects (angular relationships) between all planets in both birth charts. Each aspect is weighted by the planets involved — for example, a Venus-Mars trine carries more romantic significance than a Mercury-Saturn sextile. The result is a nuanced percentage that reflects the overall energetic harmony between two people.
Exceptionally strong harmony across multiple dimensions. Natural understanding and powerful mutual attraction. These partnerships often feel fated.
Solid compatibility with complementary energies. Some areas of easy flow and others requiring conscious effort — the hallmark of a rewarding partnership.
Significant contrasts that drive mutual evolution. These relationships push both partners beyond their comfort zones — challenging but deeply transformative.
Maximum tension between planetary energies. When navigated consciously, these pairings produce the most profound personal growth and deep understanding.
| Feature | Free | Pro |
|---|---|---|
| Planets analysed | 5 inner planets | All 10 planets |
| Compatibility dimensions | 5 scores + radar chart | 5 scores + radar chart |
| Aspect interpretations | Inner planet aspects | 270+ interpretations |
| Strengths & challenges | ✓ Grouped report | ✓ Extended report |
| Outer planet aspects | ✗ | ✓ Jupiter–Pluto |
| PDF export | ✗ | ✓ Downloadable |
| Saved reports | Up to 3 | Unlimited |
| Priority support | ✗ | ✓ |
Each planet governs a different dimension of your relationship. Understanding what each planet represents helps you interpret your compatibility report more deeply.
| Planet | Governs | Tier |
|---|---|---|
| ☀️ Sun | Core identity, ego | Free |
| 🌙 Moon | Emotions, instincts | Free |
| ☿️ Mercury | Communication, thought | Free |
| ♀️ Venus | Love, beauty, values | Free |
| ♂️ Mars | Desire, drive, conflict | Free |
| ♃ Jupiter | Growth, optimism | Pro |
| ♄ Saturn | Structure, commitment | Pro |
| ⛢ Uranus | Freedom, surprise | Pro |
| ♆ Neptune | Dreams, illusion | Pro |
| ♇ Pluto | Transformation, power | Pro |
Aspects are the angular relationships between planets in two charts. Each aspect type creates a distinct energy pattern in your relationship.
Two planets merge their energies completely. The most powerful aspect — amplifies both harmony and challenge depending on the planets involved.
A gentle, supportive connection that creates easy communication and mutual appreciation. Requires some conscious effort to activate its full potential.
Creates friction, challenge, and dynamic growth. Squares generate the energy that drives relationships forward — uncomfortable but productive.
The most naturally harmonious aspect. Trines create effortless understanding and ease — though too many trines can lead to complacency.
Creates magnetic attraction between opposite energies. Oppositions produce the "opposites attract" dynamic — complementary but requiring balance.
An awkward angle requiring constant small adjustments. Quincunxes create a nagging sense of misalignment that, when addressed, builds deep adaptability.
| Factor | Sun Sign | Synastry Calculator |
|---|---|---|
| Input required | Birth date only | Birth date, time, and location |
| Planets considered | 1 (Sun) | 10 (Sun through Pluto) |
| Aspects analysed | 1 angular relationship | 45+ planetary aspects |
| Accuracy level | General personality match | Precise energetic blueprint |
| Personalisation | Same for all born under a sign | Unique to your exact birth moment |
| Best for | Quick curiosity check | Serious relationship insight |
Sun sign compatibility is a fun starting point — and our zodiac compatibility guide covers all 78 sign pairings. But for genuine relationship insight, a synastry calculator that considers all planetary positions provides a dramatically more accurate and personalised picture. Think of it as the difference between knowing someone's nationality versus knowing their full life story.