Synastry Chart Calculator: Compare Two Birth Charts
Free synastry chart calculator: compare two birth charts from birth date, time and city. See your strongest links, friction points and house overlays, read for love, friendship, family or work.
The direct answer: A synastry chart compares two birth charts planet by planet. The angles between your planets and theirs show where the connection flows and where it rubs, and the houses their planets fall in show which parts of your life the relationship touches.
Example synastry reading
You: born July 15, 1990 at 12:00 p.m. in New York. Them: born February 14, 1988 at 6:30 a.m. in Houston.
Band: Balanced mix: warm, with a few things to work on.
A fair mix of easy and tense contacts at a moderate intensity. It is a steady base, and the growth comes from working on the friction points below.
As a couple, the contact to lean on is your Venus trine their Sun (affection that shows).
As a couple, the contact to handle with care is your Venus opposite their Mars (classic chemistry).
Your strongest links
Your Venus trine their Sun (affection that shows). Their Sun trines your Venus, a natural affection that makes dates, gifts and everyday kindness feel effortless.
Your Moon trine their Mars (heat and sensitivity). Your Moon trines their Mars: action meets feeling well. Their drive tends to protect and lift you, and your instincts help aim that drive.
Your Moon sextile their Sun (the classic pairing). Their Sun sextiles your Moon, a friendly match between purpose and feeling. It grows stronger with shared routines, small check-ins and time spent side by side.
Friction points
Your Venus opposite their Mars (classic chemistry). Your Venus opposes their Mars, a magnetic attraction across a difference. It is exciting and can swing between closeness and distance.
Your rising opposite their Venus (visible attraction). Their Venus opposes your rising, on the partnership angle of your chart. A well-known marker of attraction and commitment in synastry.
Your rising square their Moon (instant comfort). Their Moon squares your rising: your manner can unsettle their mood at times. Patience with each other's defaults goes a long way.
House overlays
Their Venus in your 7th house. Their Venus falls in your 7th house of partnership, one of the best-known love placements in synastry.
Their Jupiter in your 7th house. Their Jupiter falls in your 7th house: generous, supportive partnership energy. Their presence tends to bring good things into your life.
Their Sun in your 5th house. Their Sun lights up your 5th house of romance and fun. Dating feels playful, and it brings out your lighter side.
Your Venus in their 5th house. Your Venus falls in their 5th house of romance, a classic sign of a fun, affectionate love life.
In three lines
Balanced mix: warm, with a few things to work on.
Best link: your Venus trine their Sun (affection that shows).
Work on: your Venus opposite their Mars (classic chemistry).
Synastry describes tendencies between two charts, not outcomes. For self-reflection and entertainment; not relationship, medical, legal or financial advice.
Enter both birth dates, times and cities in the calculator on this page and pick romantic, friendship, family or work for your own reading. Computed with Swiss Ephemeris.
What is a synastry chart?
Synastry is the astrology of relationships. Instead of reading one birth chart, it lays two charts side by side and looks at how each person’s planets meet the other’s: your Venus and their Mars, your Moon and their Sun, your rising sign and their Saturn.
Sun-sign compatibility compares one point in each chart. A synastry chart compares every planet with every planet, plus the rising sign when birth times are known, which is why two people with “incompatible” Sun signs can still have a strong connection, and the other way round.
How to read your synastry
Strongest links
Trines and sextiles between your planets and theirs, plus Mars conjunctions that add spark. These are the parts of the connection that work without much effort.
Friction points
Squares, oppositions and Saturn conjunctions. They are not red flags: they are where the two of you see things differently, and where talking things through pays off most.
House overlays
Where their planets fall in your houses, and yours in theirs. Their Venus in your 7th house reads very differently from their Venus in your 10th: same planet, different part of your life.
The band
A summary of how many tight contacts there are and how many of them flow. Bands describe the texture of a connection; there is no score out of 100 because a number would claim more precision than astrology has.
The five synastry bands
Easy flow (affection that does not need forcing): Most of the tight contacts between the charts flow. Things come together easily; the work is not coasting.
Magnetic but work-y (a strong pull with real edges): Many tight contacts, both easy and tense. A strong pull with real edges, at its best when you talk early.
Balanced mix (warm, with a few things to work on): A fair mix of easy and tense contacts at a moderate intensity. A steady base with a few things to work on.
Growth match (you stretch each other): More tense contacts than flowing ones. A bond that asks for effort and tends to change both people.
Slow build (a connection that grows with time): Few tight contacts. The connection is shaped more by time and shared experience than by an instant click.
Love, friendship, family or work
Pick the kind of relationship before you read. The contacts between two charts are the same either way, but what they mean is not: Venus meeting Mars reads as attraction between partners, a creative spark between friends and drive meeting polish between coworkers.
Friendship, family and work readings never use romantic language, and each type looks at the houses that matter for it: the 11th house of friends, the 4th house of home, the 6th and 10th houses of work.
Synastry or sign compatibility?
Looking for a quick read by zodiac sign? The sign compatibility check and the compatibility guide compare Sun signs, and the Venus and Mars compatibility pages compare those two planets on their own. This page is the full two-chart version.
Both charts are computed with Swiss Ephemeris in the tropical (Western) zodiac from each birth date, time and city. Every planet from the Sun to Saturn, the North Node and the rising sign in one chart is compared with every one in the other, using standard Western orbs (8° for the Sun and Moon, tighter for the rest).
Each contact is weighted by the planets involved and how close it is to exact, and contacts that would repeat the same meaning are listed once. House overlays use whole-sign houses from each person’s rising sign.
What this page can NOT tell you
Synastry describes tendencies between two charts. It cannot tell you whether a relationship will last or what either person will choose.
Without a birth time, that person’s Moon, rising sign and houses are left out rather than guessed, so the reading is shorter. Add both times for the full picture.
This first version reads the Sun through Saturn, the North Node and the rising sign. Contacts to Uranus, Neptune and Pluto are not interpreted yet.
Frequently asked questions
What is a synastry chart?
A synastry chart compares two birth charts to see how the people relate. It lists the aspects between one person’s planets and the other’s, and where each person’s planets fall in the other’s houses. Astrologers use it for couples, friends, family and business partners.
Is synastry the same as zodiac sign compatibility?
No. Sign compatibility compares two Sun signs. Synastry compares every planet in both charts, plus the rising signs when birth times are known, so it can show a strong Moon or Venus link between people whose Sun signs look like a poor match.
Do we both need exact birth times for synastry?
Not to start. Birth dates and cities are enough for the planet-to-planet contacts. Without a time, that person’s Moon, rising sign and houses are left out, because the rising sign changes about every two hours and the Moon moves about 13° a day.
What are house overlays in synastry?
House overlays show where one person’s planets land in the other person’s houses. Their Venus in your 7th house points the connection at partnership; their Mercury in your 3rd points it at everyday conversation. They need the host’s birth time, because houses are counted from the rising sign.
Why does this synastry calculator show a band instead of a percentage?
A percentage suggests a precision that astrology does not have, so the reading uses five bands that describe the texture of a connection: Easy flow, Magnetic but work-y, Balanced mix, Growth match and Slow build. The example pair on this page reads as Balanced mix, with your Venus trine their Sun as the strongest link.
Does synastry work for friends, family and coworkers?
Yes. The contacts are the same; the reading changes. Choose friendship, family or work and the lines are rewritten for that relationship, with no romantic language, and the overlays focus on the houses that matter for it.
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The astrology is not written from memory: every chart position, dasha period and panchang timing AskSoma shows is computed with the Swiss Ephemeris on the Lahiri (Chitrapaksha) ayanamsa. How we calculate.