Composite chart calculator: one chart for the two of you
A composite chart is a single chart for two people, with every planet placed halfway between its positions in their two birth charts.
Birth time is optional: without it you still get the composite Sun, Venus and Mars.
How the midpoints are found
The zodiac is a 360° circle starting at 0° Aries, so each planet is one number on it. Two numbers split it into two arcs whose midpoints sit exactly opposite each other. For every planet the calculator takes the midpoint of the shorter arc, which lies between the two placements; the other faces away from both.
Example: A was born on 29 September 1990 at 09:30 in Moscow, B on 14 March 1988 at 22:15 in New York. A’s Sun is at 5°49′ Libra, B’s at 24°46′ Pisces. The shorter arc, 169° long, runs from Libra through Scorpio, Sagittarius, Capricorn and Aquarius; halfway along it is the composite Sun, 0°18′ Capricorn. The other midpoint, 0°18′ Cancer, lies on the longer arc and is not used. For Venus the shorter arc runs backwards, from 27°09′ Virgo through Leo, Cancer and Gemini to 9°38′ Taurus, putting composite Venus at 18°24′ Cancer. The same rule gives the Moon (6°40′ Aquarius), Mars (28°03′ Pisces) and the Ascendant (5°16′ Scorpio).
Without a birth time, a person’s chart is cast for local noon. Every planet but the Moon moves at most a degree or two a day, so those midpoints barely shift. The Moon covers about 13° a day, so the composite Moon can drift up to about 7° either way; if that crosses a sign boundary, both signs are shown. The Ascendant and Midheaven circle the zodiac daily and need both times.
The composite treats the relationship as a being in its own right. Synastry, calculated on its own page, is the two birth charts talking to each other. The first tells you what you are together; the second, what you do to each other.
A Davison chart is another method: a real chart, with a real sky and houses, cast for the midpoint in time and space between the births. Its planets stand where they really were, so they can differ from the composite midpoints, the Moon most of all. Only the composite is calculated here.
Composite chart questions
What does a composite chart mean in astrology?
It is the chart of a relationship rather than of a person, with each planet at the midpoint between the two partners’ placements. Astrologers read it much like a birth chart: the composite Sun shows what the relationship is for, the Moon how it feels from the inside and the Ascendant the face it shows the world. Its planets often fall in signs neither partner has; in the worked example on this page, a Libra Sun and a Pisces Sun make a Capricorn composite Sun.
Can you do a composite chart without a birth time?
Yes: two birth dates and places are enough for the composite Sun, Mercury, Venus, Mars and the slower planets. The hour matters for the composite Moon, which may come with two possible signs and is left out of the aspects, and for the Ascendant and Midheaven, which appear only when both times are known. Knowing the time for one of you roughly halves the Moon’s margin.
Are composite charts accurate?
The arithmetic is exact: with both birth times, every composite position here is correct to a fraction of a degree, and without them only the Moon has a wide margin. Whether the chart fits your relationship is another matter, one of astrological interpretation rather than calculation. Read the placements as descriptions to test against your own experience, and keep what holds up.
Composite chart vs synastry: what is the difference?
Synastry compares two charts, while a composite chart turns them into one. The composite describes the couple as a single unit, what the two of you are together; synastry sets one person’s planets against the other’s, such as one partner’s Moon on the other’s Saturn, and shows what each of you does to the other. Use the composite to ask what the relationship is for, and synastry to see where you attract or clash.
Davison chart or composite chart?
Neither is more correct; they are two ways of making one chart for a couple, and this calculator makes the composite. The composite takes the midpoint of each pair of positions, while a Davison chart is an ordinary chart cast for the date, time and place halfway between the two births. Choose the Davison if you want the chart of a moment that really happened, with a real sky; choose the composite if you want every point to sit exactly between the two people’s own.
Is this composite chart calculator free?
Yes: the whole result is free and needs no account or sign-up. Names are optional and never leave your device, and nothing you enter is saved.