Free Synastry & Compatibility Calculator

Enter both birth details to reveal your cosmic chemistry.

Get your complete relationship analysis — communication, conflict, and future potential.

Learn

What is a Synastry Chart?

A synastry chart compares two birth charts to reveal relationship dynamics and compatibility. Unlike simple Sun sign compatibility, synastry analyzes how all planets in both charts interact — creating a detailed picture of romantic potential, emotional connection, and possible challenges.

Key synastry aspects include: • Venus-Mars connections — Physical attraction and romantic chemistry • Moon aspects — Emotional compatibility and nurturing • Mercury contacts — Communication styles • Saturn aspects — Long-term stability and commitment potential

☀️

Sun Sign

Your core identity, ego, and life purpose

🌙

Moon Sign

Your emotional nature, inner self, and instincts

⬆️

Rising Sign

How others perceive you and your outward personality

Why Use the Sonder Synastry Calculator?

Professional-grade astrology tools trusted by astrologers worldwide

Complete Chart Comparison

We analyze all planetary aspects between both charts, not just Sun signs. Discover the full picture of your relationship dynamics.

Chemistry Scores

Get clear compatibility scores for physical attraction, emotional connection, communication, and long-term potential.

Red Flag Alerts

Our AI identifies challenging aspects that may create conflict, helping you navigate relationship dynamics consciously.

Reviews

What Users Are Saying

Join thousands of users who trust our birth chart calculator

Emily R.

@emilyrose_astro

“This birth chart calculator is incredibly accurate! The Rising sign matched exactly with my birth certificate time. The email breakdown was super helpful, and the Sonder app takes it to another level with daily updates.”

2 weeks ago

Marcus T.

@cosmic_marcus

“Finally found a free natal chart calculator that uses Swiss Ephemeris! As a student of astrology, accuracy matters. This is now my go-to tool for quick chart calculations.”

1 month ago

Sarah K.

@sarahkstars

“I love how it explains the Big 3 in simple terms! Sent the report to my mom and she finally understands why I'm so "emotional" (Cancer Moon lol). Great for beginners!”

3 weeks ago

Trusted by 50,000+ users

⭐4.9 average rating

Swiss Ephemeris certified

Guide

How to Read Your Synastry Results

Your synastry results show how planets from Person A's chart interact with planets in Person B's chart. Harmonious aspects (trine, sextile) indicate natural flow and compatibility, while challenging aspects (square, opposition) reveal growth areas and potential friction.

Pay special attention to: • Overall Compatibility Score — A weighted average of all aspects • Venus-Mars Score — Physical and romantic attraction • Moon Score — Emotional understanding and comfort • Saturn Contacts — Commitment and long-term viability

Tools

Explore More Calculators

Discover other astrology tools to deepen your cosmic understanding

🌌

Birth Chart

Discover your cosmic DNA

💍

Juno Sign

Discover your soulmate traits

🔗

Composite

Your relationship chart

View All Astrology Tools

Learn More

Deepen your understanding with our astrology guides

Starry night sky representing the cosmos and astrological charts

Guides

What is a Birth Chart? Complete Beginner's Guide

Everything you need to know about natal charts and how to read them.

8 min read

Celestial illustration of sun moon and stars

Astrology 101

Your Big 3 Explained: Sun, Moon & Rising

Understanding the three most important placements in your chart.

6 min read

Sunrise over mountain horizon symbolizing the Ascendant

Deep Dive

Why Your Rising Sign Matters More Than You Think

The Ascendant shapes how others see you and your life path.

7 min read

Browse All Articles

Glossary

Key Astrology Terms

Learn the vocabulary of the stars

Ascendant

Your Rising sign, the zodiac sign on the eastern horizon at birth

Natal Chart

A map of the sky at your exact moment of birth

Aspects

Angular relationships between planets in your chart

Houses

The 12 areas of life represented in your chart

Stellium

Three or more planets in the same sign or house

Retrograde

When a planet appears to move backward in the sky

Explore Full Glossary

FAQ

Frequently Asked Questions

Everything you need to know about using our astrology calculator

Yes, significantly. Sun sign compatibility only considers one planet, while synastry analyzes all planets and houses in both charts. This gives a much more nuanced and accurate picture of relationship dynamics.

Synastry reveals compatibility patterns and potential challenges, but free will always plays a role. Strong Saturn aspects suggest longevity, while challenging aspects highlight areas requiring conscious effort.

Challenging aspects (squares, oppositions) are not necessarily negative — they often indicate passion and growth opportunities. The key is awareness. Our report helps you understand how to navigate these dynamics constructively.

Carry the Universe in Your Pocket

Unlock daily cosmic insights, AI-powered readings, and connect with your celestial community.