Synastry & Relationship Astrology: How Compatibility Really Works
Be honest — the second you got into astrology, you compared your chart with your crush’s. Everybody does it. That delicious “are we actually compatible?” question has a real name: synastry, the heart of relationship astrology. And it’s so much juicier (and more useful) than “Sagittarius + Virgo = doomed.”
In this guide we’ll demystify synastry and astrology compatibility: what it is, which planets actually matter, the green flags and red flags, and how astrologers read two birth charts together without resorting to clickbait. (New to charts? Start with our guide on how to read a birth chart, then come back.)
WHAT IS SYNASTRY? (THE SHORT VERSION)
Synastry is the astrological practice of comparing two birth charts to understand the dynamic between two people. You lay one person’s chart over the other’s and study how their planets “talk” to each other. It’s used for romance, friendships, family and business — anywhere two humans meet.
How relationship astrology actually works
Forget sun-sign-only compatibility (“I’m a Leo, you’re an Aquarius, it’ll never work”) — that’s the horoscope-magazine version. Real synastry overlays two full charts and looks at how each person’s planets land on the other’s. Suddenly you’re not comparing two signs; you’re reading a whole living relationship.
The planets that matter most for compatibility
When you’re reading astrology compatibility, these are your VIPs:
- Sun — core identity. Do they “get” who you really are?
- Moon — emotional needs. This is the big one for feeling safe and at home together.
- Venus — love, affection and what you value. Pure relationship gold.
- Mars — drive, passion and, yes, the spark. (Also how you’ll argue.)
- Rising/Ascendant — instant chemistry and first impressions.
When these planets form close connections between two charts, things get interesting — fast.
Green flags and red flags in a synastry chart
Aspects between the two charts are where the story lives:
- Green flags: Sun-Moon connections (deep understanding), Venus-Mars (chemistry), and harmonious trines and sextiles (easy flow).
- Spicy flags: Mars-Mars or Mars-Venus squares — passion and Not bad, just intense.
- Growth flags: Saturn contacts (commitment and lessons) and Pluto contacts (deep, transformative, sometimes obsessive).
Here’s the grown-up truth no clickbait will tell you: there’s no such thing as a “bad” chart match. Every pairing has easy bits and growth bits. Synastry shows you the terrain — what you do with it is up to you.
It’s not just for romance
Relationship astrology works for any two people: best friends, a parent and child, business partners, even you and your boss. The same tools reveal why some people feel like home and others feel like homework.
Bonus: the composite chart
Want to level up? The composite chart blends two charts into a single one that represents the relationship itself — as if the bond were its own little being with its own personality. It’s a favourite tool of professional relationship astrologers, and a beautiful next step once you’ve got synastry down.
Why this skill is in such demand
“Are we compatible?” might be the single most-asked question in all of astrology. Relationship readings are some of the most requested (and most repeat-booked) sessions an astrologer can offer. Learn synastry well and you’ll never be short of curious, loved-up clients.
WANT TO READ LOVE LIKE A PRO?
Our Relational Astrology course ($1,399 → $999) teaches synastry, composite charts and the art of reading two charts together with depth and care. Brand new to astrology? Begin with Basic Astrology ($1,697 → $1,397) first, or grab the full 7-course bundle ($8,689 → $7,777, save 10%). Start at american-astrology.com.
Are you two compatible?
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Frequently asked questions
What is synastry in astrology?
Synastry is comparing two birth charts to understand the relationship between two people — how their planets interact, where it flows, and where it challenges.
Which planets matter most for compatibility?
The Sun, Moon, Venus, Mars and Rising sign do the heavy lifting in any astrology compatibility reading.
Can astrology predict if a relationship will last?
No chart guarantees an outcome. Synastry shows strengths and growth areas — the rest is down to the two real humans involved.
Do I need both people’s birth times?
For a full synastry reading, yes — accurate times give you the Moon, Rising and houses, which matter a lot for compatibility.