Synastry chart calculator
See how your charts match. A free synastry chart for you and your person.
Both birth times give the Moon and the angles; without them the result is marked approximate.
Two charts, compared
The calculator compares every planet in one chart with every planet in the other. The score is a reading aid, not a verdict on the relationship.
Compare two birth charts for compatibility. Synastry shows where one person's planets land in the other person's chart, which contacts are easy and which ones ask for work. It is a reading aid, not a verdict on whether a relationship can succeed.
How this is calculated
The position
Both charts are calculated from their own birth data and time zones, then every planet in one chart is compared with every planet in the other.
The zodiac
The major aspects are used with wider orbs for the Sun and Moon. Each contact is weighted by exactness and by whether it is a flowing or a friction aspect.
The clock
The score is a summary of the contacts, not a probability. Two charts can have a low score and a strong relationship, or a high score and a lot of work to do.
What is a synastry chart?
A synastry chart places two birth charts side by side, or one inside the other, so you can see how one person's planets connect with the other person's. It is the main tool astrologers use to look at compatibility.
Sign matching on the zodiac compatibility pages compares Sun signs only. Synastry uses the exact degree of every planet in both charts, which is why two couples with the same Sun signs can have very different synastry.
How to read a synastry chart, step by step
Read a synastry chart in layers, starting with each person on their own and ending with the contacts between you.
- Read each chart by itself first. Know each person's Sun, Moon and rising sign and what they need. The birth chart calculator and the guide on how to read a birth chart help here.
- Look at the big picture. Notice whether the contacts between you are mostly flowing (trines and sextiles) or mostly tense (squares and oppositions), and which planets keep showing up.
- Find the tightest aspects. A contact within one or two degrees is felt more strongly than one at five or six. Start with the Sun, Moon, Venus, Mars and the ascendant.
- Check the house overlays. See which of your houses the other person's planets fall into, and the other way around.
- Finish with the composite chart, which reads the relationship as a thing of its own.
The five major aspects in synastry
An aspect is the angle between a planet in one chart and a planet in the other. These five do most of the work.
Conjunction (0 degrees)
The two planets sit together. This is the strongest contact, and it blends the two energies. Your Venus on their Sun can feel like instant recognition. A conjunction can be easy or intense depending on the planets involved.
Opposition (180 degrees)
The planets face each other across the chart. This often brings attraction along with a pull between opposite needs. It works best when both people treat the other side as a balance, not a threat.
Trine (120 degrees)
The planets usually sit in signs of the same element. Trines feel easy and natural, as if you already speak the same language. The risk is taking that ease for granted.
Square (90 degrees)
The planets sit in signs that rub against each other. Squares bring friction, spark and growth. They can feel like the same argument coming back, and also like the reason you keep each other moving.
Sextile (60 degrees)
A friendly, helpful contact. Sextiles open doors, but they usually need a little effort from both people to turn into something real.
Key pairings to look for
Some planet pairs say more about a relationship than others. These are the ones most astrologers check first.
Sun and Moon
One person's Sun touching the other's Moon is a classic sign of compatibility. The Sun person often feels seen and supported, and the Moon person feels warmth and direction. A conjunction, trine or sextile is the easiest form.
Venus and Mars
This pairing describes attraction and chemistry. Venus shows what someone finds lovely, and Mars shows how someone goes after what they want. A strong Venus and Mars contact often feels like physical spark.
Moon and Moon
Comparing both Moon signs shows how your emotional needs fit. Moons in harmony make it easier to comfort each other. Moons in tension mean you may need to learn how the other person likes to be cared for.
Saturn contacts
When one person's Saturn touches the other's Sun, Moon or Venus, the bond can feel serious, loyal and long term. It can also feel heavy or critical at times. Many lasting couples have Saturn contacts, because Saturn is the planet of commitment.
House overlays in brief
House overlays show which area of your life the other person's planets light up. If their Venus falls in your seventh house of partnership, you may see them as partner material. If their Mars falls in your tenth house, they may push your career forward.
Overlays need the birth time of the person whose houses you are using, because the houses start from the rising sign. The guide to houses in astrology explains what each house covers.
Synastry without a birth time
You can still read synastry without birth times, but some parts drop out. The planets from Mercury out to Pluto move only a degree or two a day at most, and the Sun moves about one, so most aspects stay reliable.
Three things become uncertain. The Moon moves about 12 to 15 degrees a day, so its exact degree, and sometimes its sign, may be off. There is no rising sign or midheaven to compare. And there are no house overlays. In that case the calculator uses a noon chart and labels the result as approximate.
Synastry vs composite chart
Synastry shows how two people affect each other. A composite chart blends the two charts into one, using the midpoint of each pair of planets, and describes the relationship as its own thing.
Think of synastry as the conversation between you, and the composite as the room you build together. Use synastry for the day to day dynamic and the composite for the purpose and feel of the relationship. The guide what is synastry goes a little deeper.
Questions
What is a good synastry score?
There is no universal good score. A high number means more easy contacts; a lower one means more friction. Friction is not failure. The useful question is which specific contacts repeat and what they ask of each person.
Do I need both birth times?
For planets, no. For the Moon and the angles, yes. Without a birth time the calculator uses a noon chart and marks the result as approximate, and it cannot compare the rising signs.
Is synastry the same as a composite chart?
No. Synastry compares two charts planet by planet. A composite chart takes the midpoint of the two charts and reads the relationship as its own chart. They answer different questions and are best read together.
Can synastry predict a breakup?
No. It describes patterns and pressures, not outcomes. People make relationships work or not with choices, timing and support that no chart contains.
Which aspects matter most in synastry?
The tightest contacts between the Sun, Moon, Venus, Mars and the Ascendant usually matter most. Sun and Moon, Venus and Mars, and Saturn touching a personal planet are the pairings most astrologers check first.
What if our synastry has mostly squares and oppositions?
That does not mean the relationship will fail. Tense aspects bring friction and growth, and many strong couples have plenty of them. It usually means you need to talk more openly about the places where you clash.
Can synastry be used for friends or family?
Yes. Synastry works for any two people: friends, siblings, parents or coworkers. Venus and Mars contacts matter less outside romance, while the Sun, Moon and Mercury show how you get along day to day.