How to Read a Synastry Chart: A Step-by-Step Guide

A synastry chart puts two birth charts side by side, or more often one inside the other, so you can see how the planets of one person relate to the planets of another. It's the core technique of relationship astrology, and it says far more than comparing two Sun signs ever could.

It can also look overwhelming: two rings of glyphs and a web of lines. This guide explains what you're looking at and gives you an order for reading it.

What Is a Synastry Chart?

Synastry is the comparison of two birth charts. Most tools show it as a bi-wheel: one person's chart forms the inner wheel, with their houses, and the other person's planets are placed around the outside at their own zodiac positions.

Two kinds of information come out of that comparison:

Inter-aspects: angles between a planet in one chart and a planet in the other. Person A's Venus trine Person B's Moon, for example.
House overlays: which of one person's houses the other person's planets fall into. Person B's Sun landing in Person A's seventh house, for instance.

A synastry chart isn't a third chart. That's the composite chart, which builds a single chart from the midpoints between the two people's placements and is read as the relationship's own identity. Synastry stays with the two individuals and asks how they affect each other.

What Do You Need to Compare Two Charts?

The same data as for a single birth chart: date, time and place of birth for both people. Without birth times you can still calculate most inter-aspects, but you lose the Ascendants, house overlays, and possibly certainty about one or both Moons. You can compare two charts for free with our synastry tool, which draws the bi-wheel and lists the main contacts.

Which Synastry Aspects Matter Most?

Not all contacts carry equal weight. A practical hierarchy:

1. Contacts involving the personal planets and angles

The Sun, Moon, Mercury, Venus, Mars and the Ascendant describe the most personal, day-to-day parts of each person. Contacts between them tend to be the ones people actually notice.

Sun–Moon: one of the classic markers of compatibility in astrology, especially by conjunction, trine or opposition. Read as identity meeting emotional need.
Moon–Moon: how two emotional rhythms line up; whether comfort comes naturally or needs translating.
Venus–Mars: the traditional signature of attraction and desire.
Mercury–Mercury and Mercury–Moon: ease of conversation and feeling understood.
Planets on the other person's Ascendant: read as a strong first impression and a sense of being "seen".

2. Saturn contacts

Saturn touching a partner's Sun, Moon or Venus is traditionally associated with commitment and seriousness, and sometimes with a sense of restriction or criticism. Many long-term couples have notable Saturn contacts, which is why astrologers don't treat them as simply negative.

3. Jupiter contacts

Jupiter on a partner's personal planets is read as generosity, encouragement and a sense that the other person makes life bigger.

4. Outer planets and the nodes

Contacts from Uranus, Neptune and Pluto are read as excitement and instability (Uranus), idealization or confusion (Neptune), and intensity or power dynamics (Pluto). Bear in mind that people born within a few years of each other share similar outer-planet positions, so these contacts are less individual than they look. The North Node is sometimes read in synastry as a sense of direction or "fated" familiarity; treat that symbolism lightly.

How Close Does an Aspect Need to Be?

The distance from exactness is called the orb. In synastry, most astrologers use slightly tighter orbs than in a single birth chart, because two full charts produce many contacts and wide orbs make almost everything look connected. Elencya's synastry uses 6° for conjunctions and oppositions, 5° for trines and squares and 4° for sextiles.

Within that, tighter is stronger: a Venus–Mars conjunction within 1° is a far more central theme than one at 5°.

How Do House Overlays Work?

House overlays answer: "in which area of my life do I experience this person?" If your partner's Venus falls in your fourth house, the symbolism points to home and family; in your tenth, to ambitions and public life; in your seventh, to partnership itself.

Overlays work in both directions and are often asymmetrical. One person may experience the relationship as mostly about daily routine (sixth house), the other as mostly about romance and play (fifth house). That asymmetry is often more revealing than any single aspect. They require accurate birth times for the person whose houses you're using; our guide to the astrological houses explains each one.

A Step-by-Step Way to Read a Synastry Chart

Start with the basics of each chart. Know each person's Sun, Moon, Venus, Mars and Ascendant separately first. Our rising sign calculator gives you the big three for each person.
List the tightest inter-aspects involving personal planets. Ignore the rest for now.
Group them by theme: emotional bond (Moon), attraction (Venus, Mars), communication (Mercury), commitment (Saturn), growth (Jupiter).
Check the house overlays for the Sun, Moon, Venus and Mars of each person.
Look for repeated themes. If several contacts point to strong communication, that's more meaningful than a single trine.
Read the tensions honestly. A Mars–Saturn square between charts can describe one person's pace frustrating the other's caution. That's useful to know, not a doom sign.

Common Mistakes When Reading Synastry

Counting aspects like a score. Ten trines don't add up to a good relationship, and three squares don't sink one.
Treating "difficult" contacts as deal-breakers. Friction is part of every relationship, astrological or not.
Reading only one direction. Venus in your seventh house and their Saturn on your Moon are both part of the story.
Over-reading outer-planet contacts shared by everyone born in the same few years.
Using the chart as permission. No contact justifies behavior that isn't respectful.

When Is a Full Synastry Report Worth It?

The free tool shows the bi-wheel and the most important contacts. If you'd like every relevant contact interpreted and organized by theme (attraction, emotional bond, communication, commitment, shared growth), the love compatibility report does that for two charts. For a quicker, sign-level view, start with zodiac compatibility explained.

What Synastry Can and Can't Tell You

Synastry is a detailed symbolic description of how two people's charts interact, and many couples find it a helpful way to talk about their differences. It can't measure love, predict whether a relationship will last, or tell you whether to commit, stay or leave. How two people actually treat each other is always the better evidence.