Relationship Astrology Tool

Synastry Compatibility Calculator

Enter two birth charts to discover the planetary aspects, connection points and relationship dynamics between any two people.

1. Planet-to-Planet Aspects

Synastry compares each planet in one chart to every planet in the other, finding conjunctions, trines, squares and oppositions that describe attraction, friction and growth.

2. Compatibility Scoring

Each aspect is weighted by planet, type and orb to produce scores across love, communication, stability and growth — your personal compatibility profile.

3. Relationship Reading

The strongest aspects become a personalised reading describing the nature of the connection, what flows naturally, and where growth is needed.

A Person 1
B Person 2
A & B
Synastry Analysis
Overall Compatibility
Relationship Reading
Relationship Pattern
Green Flags & Growth Edges
Where You Affect Each Other
Planet Positions
Planet Person A Person B
Synastry Aspects

What Is a Synastry Chart Calculator?

A synastry chart calculator overlays two birth charts and maps every planetary aspect formed between them. Where your planets land in someone else's chart — and how they interact — reveals the energetic chemistry, emotional resonance, friction points and long-term potential of any relationship.

Unlike a generic Sun-sign compatibility reading, a synastry compatibility calculator uses the complete birth chart of both people — every planet, angle and house — to build a precise, personal picture of how two people actually experience each other.

How Synastry Works

Planet-to-Planet Aspects

When one person's planet forms a conjunction, trine, square or opposition to another's, a specific relational dynamic is created. Trines and sextiles bring ease. Squares bring tension and growth. Conjunctions intensify whatever they touch.

House Overlays

Where your planets fall in your partner's houses reveals which area of their life you activate. Your Venus in their 7th house suggests romantic pull. Your Saturn in their 10th may create pressure around their career and ambitions.

Compatibility Scoring

Each aspect is weighted by planet, type and orb to produce scores across love, communication, stability, attraction and growth — your personal relationship profile based on the full chart comparison.

Key Synastry Aspects to Know

These are the most significant planetary connections in any synastry reading:

☀️ Sun conjunct Moon
The classic long-term bond indicator. One person's core identity resonates with the other's emotional nature — a feeling of being fundamentally understood.
♀ Venus conjunct Mars
Powerful romantic and physical chemistry. One person's desire (Mars) meets the other's magnetism (Venus). One of the strongest attraction indicators in synastry.
♀ Venus trine Venus
Natural harmony in values and taste. Relationships with this aspect tend to feel warm, easy and mutually appreciative — both people enjoy the same things.
♄ Saturn conjunct Sun or Moon
A serious long-term indicator. Saturn brings commitment and structure but also pressure and restriction. Common in lasting marriages — and in relationships that feel heavy or karmic.
☿ Mercury trine Mercury
Effortless communication. Both people naturally understand each other's thinking style. Conversations flow and misunderstandings are rare — a strong friendship foundation.
♃ Jupiter conjunct Venus or Sun
A relationship that feels lucky and expansive. One person's optimism amplifies the other's joy. Tends to feel uplifting, generous and growth-oriented.

Frequently Asked Questions

What is the most important aspect in synastry?
The Sun-Moon conjunction is widely considered the most significant long-term compatibility indicator — it shows a fundamental resonance between identity and emotional need. For attraction, Venus-Mars aspects are equally important. There is no single most important aspect; the full pattern matters more than any one connection.
Can synastry tell me if a relationship will last?
Synastry reveals the energetic dynamics between two people — what flows and what creates friction. Saturn aspects and strong Sun-Moon connections are associated with lasting bonds. But synastry shows the terrain, not the outcome. Free will, timing and personal growth all play a role.
What is the difference between synastry and a composite chart?
Synastry overlays two individual charts to show how two people interact. A composite chart creates one chart from the midpoints of both charts, representing the relationship itself as an entity. Synastry shows the dynamic between two people; composite shows the purpose of the relationship.
Do I need an exact birth time for accurate synastry?
An exact birth time gives the most accurate results for Ascendant and house overlays. Without a birth time, the calculator defaults to noon — planetary positions are still accurate for most planets, and the aspect analysis remains highly relevant. The Moon is the main limitation for unknown birth times as it can shift sign in a day.
Can I use this calculator for friendships or family?
Yes — synastry applies to any two people. The same aspects that create romantic chemistry can explain deep friendships, family bonds or working partnerships. House overlays are particularly revealing for understanding how two people affect each other's life areas regardless of relationship type.