Free Astrology Calculator
Synastry Chart Calculator
Compare two birth charts. Enter both people's birth details to see every aspect between your planets with exact orbs, where each person's planets fall in the other's houses, and a plain reading of the closest contacts.
What a Synastry Chart Shows
Synastry is the astrology of two people. It places one birth chart beside another and asks how the planets of one touch the planets of the other. When your Moon sits close to someone's Sun, or your Venus squares their Mars, the qualities those planets stand for meet in daily life: comfort, attraction, irritation, recognition. A synastry chart lists those meetings, with the orb that says how close each one is.
It also shows house overlays. Each house of a chart describes an area of life, so a partner's Venus in your 4th house brings affection into home and family, and their Saturn in your 10th brings seriousness to your sense of direction.
How to Read Synastry
- Start with the personal points. Contacts between the Sun, Moon, Mercury, Venus, Mars and the Ascendant are the ones people feel day to day. Outer planets matter most when they touch these.
- Weigh by orb. An aspect within 1 or 2 degrees is felt far more than one at 7. The calculator lists the closest first.
- Read both directions. Your Venus to their Mars is a different story from their Venus to your Mars. Each person experiences the contact from their own side.
- Look for repetition. When the same theme appears in an aspect, a house overlay and a sign comparison, it is likely to be a real feature of the relationship.
- Notice your own response. The chart names a quality. You are the one who knows how it actually feels between the two of you, and what you want to do with it.
The Five Aspects in Synastry
| Aspect | Angle | Orb | Quality |
|---|---|---|---|
| Conjunction | 0° | 8° | The two planets act as one. Strong in any combination, and its quality depends on the planets involved. |
| Sextile | 60° | 5° | Friendly and cooperative. Works well when either person takes it up. |
| Square | 90° | 7° | Friction that asks for adjustment. Often where a relationship feels most alive and most effortful. |
| Trine | 120° | 7° | Ease and natural understanding. Comfortable, and easy to take for granted. |
| Opposition | 180° | 8° | Attraction across a gap. Each person shows the other a missing side, and balance takes work. |
Orbs widen by up to 2 degrees when the Sun or Moon is involved, the usual allowance for the two lights.
The Contacts Astrologers Read First
- Sun and Moon
- Sun and Moon contacts join who one person is with what the other needs to feel at home. Notice whether you feel recognized, and where.
- Venus and Mars
- Venus and Mars contacts describe attraction: how one person's way of loving meets the other's way of wanting.
- Moon and Moon
- Moon to Moon describes how your moods and comforts meet, the daily emotional weather of living close.
- Mercury and Mercury
- Mercury contacts describe how you talk, listen and argue, and how easily you follow each other's thinking.
- Saturn and the Moon
- Saturn on a Moon asks for emotional reliability. It can feel safe and committed, or restrained, depending on how it is handled.
- A Planet on the Ascendant
- A Sun on the other's Ascendant is often noticed at first meeting: one person's presence lights up how the other meets the world.
Why There Is No Compatibility Score
Many synastry calculators add up aspects into a percentage. A score hides the information that matters: which planets are involved, which person feels what, and how two people choose to work with friction. A square between two Moons can be the quarrel a couple keeps having or the honest conversation that keeps them close. So this page lists the contacts, says what each one is about, and leaves the verdict to the people involved.
Synastry, Composite and Davison Charts
Synastry keeps two charts side by side. A composite chart blends them into one chart built from the midpoints between each pair of planets, read as the relationship's own character. A Davison chart does something similar with time and place: it is cast for the moment and location halfway between the two births. For sign-by-sign comparisons of the Sun, Moon, Venus and Mars, use the birth chart compatibility calculator, or read our guide to love compatibility in astrology.
Synastry Questions
What Is a Synastry Chart?
A synastry chart lays two birth charts over each other and lists the aspects between them: the angles one person's planets make to the other person's planets. It also shows house overlays, the houses of one chart where the other person's planets land. Astrologers use it to describe how two people affect each other.
How Do You Read a Synastry Chart?
Start with the closest contacts between personal points: the Sun, Moon, Mercury, Venus, Mars and the Ascendant. A tight orb is felt more strongly than a wide one. Then notice the tone of each contact (blending, flowing, friction or polarity), the houses where each person's planets fall in the other's chart, and any theme that repeats. A theme that shows up three times matters more than any single aspect.
What Are the Most Important Aspects in Synastry?
Most astrologers look first at Sun and Moon contacts, Venus and Mars contacts, Moon to Moon, Mercury to Mercury, Saturn to the personal planets, and any planet on the other person's Ascendant. These touch identity, feeling, attraction, communication and commitment, the parts of a relationship people live with every day.
Which Orbs Does This Synastry Calculator Use?
The five major aspects: conjunction and opposition within 8 degrees, trine and square within 7, sextile within 5, with up to 2 extra degrees when the Sun or Moon is involved. Contacts between two slow outer planets (Uranus, Neptune, Pluto) or the North Node are left out, because people born a few years apart share them.
Can I Do Synastry Without a Birth Time?
Yes, with limits. Without a birth time the chart is calculated for noon, so it has no Ascendant, Midheaven or houses, and the Moon could be up to about 6 degrees away in either direction. The calculator leaves that Moon out of the aspects and marks any house overlay it would affect. Every other planet moves slowly enough to be reliable.
Is Synastry the Same as Compatibility?
Synastry is the method most astrologers mean when they talk about compatibility between two whole charts. Sun sign compatibility compares only one placement each. Synastry compares every planet, so two people with clashing Sun signs can still share close Moon, Venus or Mars contacts. The birth chart compatibility calculator puts the sign comparisons first.
What Is the Difference Between Synastry and a Composite Chart?
Synastry keeps the two charts separate and shows how each person meets the other. A composite chart blends the two into one chart, built from the midpoints between each pair of planets, and is read as a portrait of the relationship itself. They answer different questions, so many astrologers use both.
Does Difficult Synastry Mean a Relationship Will Fail?
No. Squares and oppositions describe friction and pull, and many lasting relationships have plenty of both, because friction is also where people grow. Easy trines can feel pleasant and ask little. Synastry describes the qualities two people bring out in each other; what they do with them is up to them.