Guides · Synastry
Synastry chart interpretation: how to read two charts together
To interpret a synastry chart, you read each person's chart alone first, then the aspects between one person's planets and the other's, then the houses each person's planets land in on the other's chart. The closest contacts between personal planets (Sun, Moon, Mercury, Venus, Mars) carry the most weight, and a theme counts only when it repeats.
A synastry reading is not a score. It describes where two people click, where they rub, and where the work of the relationship sits. Below is the order astrologers use, the tables you need beside the chart, a worked example, and the mistakes that make most online readings sound alike. To try it on your own pair, get your free chart first, then add your partner's details.
What a synastry chart is
A synastry chart, also called a bi-wheel, puts two birth charts on one wheel. Usually one person's chart sits on the inner ring with its houses, and the other person's planets are placed on the outer ring at the same zodiac degrees. Nothing is averaged or blended: every planet stays where it was at each birth.
Three things come out of that overlay:
- Inter-aspects: the angles between your planets and theirs. Your Venus 120° from their Mars is a Venus trine Mars contact.
- House overlays: which of your houses their planets fall in, and which of their houses your planets fall in. Their Sun in your 7th house is a classic partnership overlay.
- Shared emphasis: whether the two charts lean on the same elements, the same signs or the same areas of life.
Synastry vs composite vs Sun-sign compatibility
| Method | What it uses | What it answers |
|---|---|---|
| Sun-sign compatibility | One sign each | A rough feel for two temperaments. Leaves out about nine tenths of each chart. |
| Synastry | Both full charts, side by side | How each of you affects the other: attraction, comfort, friction, who triggers what in whom. |
| Composite chart | One chart built from the midpoints of each pair of planets | The relationship as its own thing: what it is for, what it feels like from outside. |
| Davison chart | One chart for the midpoint in time and place between the births | Similar to the composite, read like a real birth chart. |
Most astrologers start with synastry and add a composite once they know the two people. If you only want a quick view of two signs, the compatibility pages cover every sign pair; synastry is the next level down.
What you need before you start
- Both birth dates. Enough for planet signs and most aspects.
- Both birth times. Needed for the Moon's exact degree (it moves about 13° a day), the rising sign, and every house overlay.
- Both birth places. The place sets the time zone and the houses. A wrong time zone shifts everything by an hour or more.
- One house system for both. Placidus and Whole Sign can put a planet in different houses. Pick one and keep it for both charts; see houses in astrology for how they differ.
If one birth time is missing
The full method, with a table of how far each planet moves in a day, is in synastry without a birth time.
You can still read a lot. Use a noon chart for that person and treat their Moon as anywhere within about 6° either side of the noon position. Then:
- Read every aspect between the Sun, Mercury, Venus, Mars, Jupiter and Saturn: those barely move in a day.
- Read their Moon's sign only if it stays in one sign all day; check the positions at 00:00 and 23:59.
- Read their planets in your houses (your time is known). Skip your planets in their houses, and skip anything to their Ascendant or Midheaven.
A birth certificate usually carries the time in the US; the CDC lists where to order one in each state. A hospital record or a parent's memory to the nearest hour is still far better than nothing.
How to read a synastry chart, step by step
This is the order that keeps you from jumping to the one aspect that sounds exciting.
1. Read each chart alone
Before comparing, know what each person brings. Look at each chart's Venus (what they enjoy and how they show care), Mars (how they go after things and handle anger), Moon (what makes them feel safe), the 7th house and its ruler (what they look for in a partner) and Saturn (where they are cautious). Someone with Venus in Capricorn shows love through reliability; no synastry aspect turns that into grand gestures. If you're new to single charts, how to read a birth chart covers the basics.
2. Compare temperaments
Count each person's planets by element (fire, earth, air, water) and by mode (cardinal, fixed, mutable), weighting the Sun, Moon and Ascendant double. Two people heavy in the same element understand each other quickly but can share the same blind spot. A chart short on an element often feels drawn to someone who has plenty of it. Note it, then move on: this sets the tone, not the details.
3. List the inter-aspects, closest first
Write down every major aspect between the two charts, then sort by orb (how far from exact). Start with the personal planets and the angles (Ascendant, Descendant, Midheaven). The table below gives common orbs; astrologers disagree on exact numbers, but they agree that tighter is stronger.
| Aspect | Angle | Common orb in synastry | How it reads between two people |
|---|---|---|---|
| Conjunction | 0° | up to 8°, 10° with Sun or Moon | The two planets act as one. Strong, for better or worse, depending on the planets. |
| Opposition | 180° | up to 8° | Pull and push. Each sees in the other what they lack; attraction with tension. |
| Square | 90° | up to 6° | Friction that gets things moving. Sparks, arguments, growth if both work at it. |
| Trine | 120° | up to 6° | Easy flow. Comfortable, sometimes so easy it's taken for granted. |
| Sextile | 60° | up to 4° | Friendly help that needs a little effort to switch on. |
| Quincunx | 150° | up to 2° | Awkward fit; the two keep needing to adjust to each other. |
4. Read what each planet pair is about
The aspect says how two planets meet; the planets say what it concerns. Read the pairs in roughly this order of weight:
| Contact | What it describes | Easy aspect | Hard aspect |
|---|---|---|---|
| Sun and Moon | Basic fit: one's identity, the other's emotional needs | Feel at home together | Love each other but misread moods |
| Venus and Mars | Physical attraction and romantic pull | Steady chemistry | Strong pull with clashes over pace |
| Moon and Moon | Daily rhythm, comfort, how you each unwind | Easy living together | Different needs when upset |
| Moon and Venus | Affection and tenderness | Warm, caring | Care given in the wrong form |
| Mercury and Mercury | Talking, planning, arguing | Finish each other's sentences | Talk past each other |
| Saturn to a personal planet | Commitment, duty, also criticism | Loyal, builds over years | One feels judged or held back |
| Jupiter to a personal planet | Generosity, encouragement | Bring out the best | Overdo it, indulge each other |
| Uranus to a personal planet | Excitement, freedom | Keep things fresh | On and off, unpredictable |
| Neptune to a personal planet | Idealism, romance, also confusion | Soft, dreamy, spiritual | Seeing what you want to see |
| Pluto to a personal planet | Intensity, change, power | Deep, transforming | Control and jealousy themes |
| Planet on the other's Ascendant | Instant noticing; first impressions | Strong either way; read by the planet | |
| Planet on the other's Descendant | Feels like "a partner type" | Strong either way; read by the planet | |
Outer-planet contacts (Uranus, Neptune, Pluto) to each other mean little between people of a similar age: those planets move so slowly that everyone born within a few years shares them.
5. Read the house overlays, both ways
Place their planets in your houses, then yours in theirs. The house shows which part of your life the other person switches on. A crowded overlay (three or more of their planets in one of your houses) is a headline.
| Their planets in your… | You tend to feel they… |
|---|---|
| 1st house | See you, affect how you look and act |
| 2nd house | Touch your money, values and sense of worth |
| 3rd house | Are someone you talk with constantly |
| 4th house | Feel like home and family |
| 5th house | Bring romance, play and fun |
| 6th house | Shape your routines and daily habits |
| 7th house | Feel like a partner, an equal, sometimes a rival |
| 8th house | Reach deep: intimacy, shared money, trust |
| 9th house | Widen your world: travel, beliefs, learning |
| 10th house | Affect your career and public life |
| 11th house | Feel like a friend; share your circle and plans |
| 12th house | Reach something private or hidden; hard to name |
The planet tells you the flavour. Their Saturn in your 5th can make dating feel serious; their Jupiter in your 5th makes it fun. Their Moon in your 4th tends to feel like family very fast.
6. Look for themes that repeat
Now step back. One aspect is a detail; the same story told three ways is the reading. If you find Venus trine Mars, their Mars in your 5th, and your Venus on their Descendant, attraction is a theme. If you find Saturn square Moon, their Saturn in your 4th and Moon square Moon, emotional safety is where the work sits. Write the two or three themes in one line each: that's your synastry interpretation.
For the contacts astrologers read as chemistry, ranked with their orbs, see synastry aspects that indicate attraction.
How to weigh one contact against another
When two contacts point in opposite directions, these rules settle most of it:
- Orb first. A square within 1° outweighs a trine at 6°.
- Personal over outer. Sun, Moon, Venus, Mars and the Ascendant matter more than Uranus, Neptune or Pluto to each other.
- Two-way beats one-way. Your Moon on their Sun and their Moon on your Sun is a double contact, among the strongest you can find.
- Repeated beats single. Three contacts about the same theme beat one striking aspect.
- Angles count. A planet within a few degrees of the other's Ascendant, Descendant or Midheaven is felt from the first meeting.
A simple tally helps. Give each contact points: 3 for an orb under 2°, 2 for 2° to 4°, 1 beyond that; add 1 if it involves the Sun, Moon or Ascendant, and 1 if it's mirrored both ways. The highest scores are the ones to read first. It's a sorting tool, not a verdict on the couple.
A worked example
An example pair, made up to show the method (not real people). Person A has the Sun at 14° Leo, the Moon at 3° Pisces and Venus at 22° Cancer. Person B has the Moon at 12° Leo, Mars at 20° Scorpio and Saturn at 5° Virgo, with both birth times known.
| Contact | Orb | Reading |
|---|---|---|
| A's Sun conjunct B's Moon | 2° | Core fit. B feels at ease around A; A feels understood. |
| A's Venus trine B's Mars | 2° | Steady attraction, both water signs: affection shown through closeness. |
| A's Moon opposite B's Saturn | 2° | A can feel B is cool or critical when A is upset; B may feel A's moods ask too much. |
The tally puts all three near the top. Two say the bond and attraction are real; the third says the work sits in how they handle bad days. A good written reading says exactly that, and then looks at houses: if B's Saturn falls in A's 4th, home is where the Saturn lesson plays out, and a shared routine for hard days would be the practical answer.
Worried about a hard contact you found? Synastry aspects to avoid ranks the ones astrologers flag, with what each asks of a couple.
Common mistakes in synastry readings
- Reading one aspect as the whole story. A single square doesn't doom anything, and a single trine doesn't guarantee anything.
- Only counting easy aspects. Long relationships usually show some squares and oppositions; they're often where the spark lives.
- Ignoring each chart alone. Someone who keeps distance by nature will do so in any synastry.
- Reading only one direction. Your planets in their houses tell a different story from theirs in yours.
- Trusting houses with a guessed time. An hour's error can move several overlays.
- Mixing house systems. Use the same one for both charts.
- Treating it as permission or a warning. A chart describes tendencies; two people decide what to do with them.
What synastry can't tell you
Synastry is a tradition of interpretation, not a tested predictor. Controlled studies have not found that astrology predicts personality (Carlson, 1985), and a study of married and divorced couples found Sun-sign pairs didn't predict who stayed together (Silverman, 1971). Read your synastry as a vocabulary for talking about how you two work, not as a forecast. If a relationship involves fear, control or harm, that's a matter for a counselor or a helpline, not a chart.
Frequently asked questions
What is the most important aspect in synastry?
Most astrologers name Sun and Moon contacts first, then Venus and Mars, then Saturn to a personal planet for staying power. The tightest aspect between personal planets in your own pair usually matters more than any list. For long-term pairs, see the synastry aspects astrologers look for in a marriage.
Do I need an exact birth time for synastry?
For aspects between most planets, no. For the Moon's exact degree, the rising sign and every house overlay, yes. With one time missing, read their planets in your houses only.
Is a synastry chart the same as a composite chart?
No. Synastry keeps both charts as they are and compares them. A composite builds one new chart from midpoints and is read as the relationship's own chart.
Can synastry be good if our Sun signs clash?
Yes. Sun signs are one contact among dozens. Two people with "incompatible" Sun signs can share Moon, Venus and Ascendant contacts that matter more day to day.
Which person goes on the inner wheel?
It doesn't change the aspects. It only changes whose houses you're looking at, so do it both ways.
Can synastry tell if someone is my soulmate?
No chart can promise that. Astrologers link strong Sun, Moon, Venus and North Node contacts with a feeling of recognition, but how a relationship goes depends on the two people.
Want to see your own pair? Start with your free birth chart, then add your partner's date, time and place. Looking for a soulmate pattern? Synastry aspects for soulmates ranks the contacts with a checklist. The guides page lists the rest of the series, including what the 12 houses mean and what your Moon sign says.
Sources
- Astrodienst (astro.com), Astrowiki: "Synastry", "Composite chart", "Aspects", "Orb". https://www.astro.com/astrowiki/
- Wikipedia, "Synastry" and "Composite chart". https://en.wikipedia.org/wiki/Synastry
- Cafe Astrology, "Summary of Techniques in Synastry". https://cafeastrology.com/synastry_astrology_relationships/
- CDC, "Where to Write for Vital Records". https://www.cdc.gov/nchs/w2w/
- Carlson, S. "A double-blind test of astrology." Nature 318, 419–425 (1985).
- Silverman, B. "Studies of astrology." Journal of Psychology 77, 141–149 (1971).
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