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Free Synastry Chart Calculator
Compare two birth charts to explore relationship compatibility, planetary aspects, house overlays, attraction, communication, and long-term relationship dynamics.
See What Your Synastry Chart Reveals
Overall Compatibility
61 / 100
Major Aspect
Moon Sextile Sun
Orb 0°07'
Sun sextile Moon opens easy goodwill between identity and emotional needs when both people lean in.
What Is a Synastry Chart?
A synastry chart compares two birth charts to show how one person's planets interact with another person's planets. In relationship astrology, synastry is used to explore compatibility, attraction, communication, emotional patterns, and long-term dynamics.
Instead of reading one natal chart alone, you overlay both charts — looking at planetary aspects between the two people and where each person's planets fall in the other person's houses. That is why a free synastry chart calculator is one of the most practical tools for birth chart compatibility.
How to Use This Synastry Calculator
- 1
Enter both birth dates
Add names if you like, then the birth date for each person.
- 2
Add birth times and locations
Exact birth time improves house overlays, Rising sign, and other angle-based details.
- 3
Generate your synastry chart
Get a chart wheel for both people, major aspects, house overlays, and compatibility scores.
Birth Chart Compatibility: What We Compare
Relationship compatibility in synastry is multi-dimensional. Our calculator scores attraction, emotion, communication, chemistry, long-term potential, and challenge patterns from planetary contacts.
Love & Attraction
Venus, Mars and 5th/8th house contacts
Emotional Compatibility
Moon contacts and 4th house overlays
Communication
Mercury aspects between charts
Sexual Chemistry
Venus–Mars and Mars–Pluto links
Long-term Potential
Saturn contacts and lasting patterns
Challenges
Squares, oppositions and Saturn contacts
Synastry Aspects Between Two Birth Charts
Major aspects show how planetary energies connect across two birth charts. This calculator highlights five core aspects: conjunction, trine, sextile, square, and opposition.
Synastry Houses & House Overlays
House overlays show where one person's planets fall in the other person's birth chart — revealing the life areas activated by the relationship.
Get Your Synastry Compatibility Report
After you calculate, your report includes overall compatibility, love & attraction, emotional connection, communication, major challenges, long-term potential, house overlays, and major aspects.
View Your Synastry ReportSynastry Chart vs Composite Chart
| Dimension | Synastry | Composite |
|---|---|---|
| What it compares | Two birth charts | Midpoint chart |
| Best for | How two people interact | Relationship as one entity |
| Main output | Aspects + overlays | Composite planets/houses |
Free Synastry Report with written interpretation →Try Composite Chart Calculator →Synastry vs Composite guide →
How to Read a Synastry Chart
Start with the lights and personal planets before diving into every minor contact. A practical reading order:
Frequently Asked Questions
- What is a synastry chart?
- A synastry chart is a comparison of two birth charts that highlights planetary aspects and house overlays between two people.
- How does a synastry calculator work?
- You enter both birth details. We adjust for each birth place’s time zone (including daylight saving), calculate precise planet positions, then map aspects, house overlays, and compatibility themes.
- Is this synastry chart free?
- Yes. This free synastry chart calculator does not require an account.
- Do I need an exact birth time for synastry?
- Planet-to-planet aspects still work without an exact time. House overlays, Rising sign, and Midheaven are much more accurate with a precise birth time.
- What is the most important aspect in synastry?
- It depends on the question — Sun/Moon for core harmony, Venus/Mars for attraction, Mercury for communication, Saturn for longevity. Explore synastry aspects.
- What is the difference between synastry and a composite chart?
- Synastry compares two charts to each other. A composite chart creates a midpoint chart that describes the relationship as its own entity. Compare synastry vs composite.
Explore Guides & Tools
- Free Synastry ReportA plain-language reading of your strongest relationship patterns.
- Synastry AspectsHow planet-to-planet contacts shape chemistry and friction.
- Synastry HousesWhere each person’s planets land in the other’s chart.
- How to Read a Synastry ChartA practical order for aspects, planets, and overlays.
- Composite Chart CalculatorSee the relationship as one midpoint chart.
- Synastry vs CompositeWhen to compare two charts versus blend them.