Composite Charts: The Relationship as a Third Chart

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A composite chart combines two birth charts into a single chart. For each planet, you take the point halfway between where it stands in one person's chart and where it stands in the other's: the midpoint of the two Suns becomes the composite Sun, the midpoint of the two Moons the composite Moon, and so on through Pluto. Astrologers read the result as a picture of the relationship as its own unit, something the two people make together, rather than a description of either person. It is a separate technique from synastry, and it describes shared themes, not how a relationship will turn out.

Educational guide: Astrologist.com does not currently calculate synastry, inter-chart aspects, house overlays or composite charts. The compatibility tool provides a sign-level estimate based on the Sun, Moon and Rising signs; known birth times are required for that tool. The contacts discussed here must be identified separately from the two charts' actual positions.

Astrologist.com does not calculate midpoint composites, Davison charts, composite aspects, composite angles or composite houses: the compatibility tool stays a sign-level Big Three estimate, the chat is not a composite calculator, and every composite and Davison position on this page was worked out separately from the two birth charts.

Composite, synastry and the compatibility tool

Three different things can be called relationship astrology, and they answer different questions:

• Synastry keeps the two charts separate and compares them contact by contact: one person's Venus to the other's Mars, one person's Moon to the other's Sun. The method is set out in comparing two charts by degree.
• A composite chart blends the two charts into one. There are no "your planet" and "my planet" any more, only the composite Sun, the composite Moon and the rest, with their own signs and their own aspects to each other.
• The Astrologist.com compatibility tool gives a sign-level estimate from both people's Sun, Moon and Rising signs. It does not look at degrees, midpoints or a third chart.

The three can disagree, because they measure different things. Two people with few synastry contacts can have a composite with a tight Sun-Moon aspect, and the reverse. Neither result overrides the other; they are different views of the same pair.

How a composite is built

Each pair of matching planets has two midpoints on the 360° circle, because two points divide the circle into two arcs. One midpoint sits in the middle of the shorter arc; the other sits exactly opposite it, in the middle of the longer arc. The worked examples here use the shorter-arc midpoint for every planet. That is the convention these articles follow, and it is a convention rather than a law: the opposite midpoint is always the alternative, and when two positions are exactly 180° apart the two midpoints are equally far from both and neither is the shorter one. If you compare a composite from another source, check which midpoint it used.

Only the matching planets are paired: Sun with Sun, Mercury with Mercury, and so on. The composite has no meaning for a pair such as one person's Venus and the other's Mars; that kind of pairing is synastry. The full arithmetic, including the wrap-around at 0° Aries, is in how to calculate a composite chart.

A worked example

The pair below is the same pair used in comparing two charts by degree, so you can set their synastry and their composite side by side. Positions come from the site's own natal routines, as the free birth chart displays them (degrees and whole minutes).

• Person A: 14 March 1988, 07:30, Amsterdam.
• Person B: 2 August 1990, 21:10, London.

The composite column was calculated from the full-precision positions and then cut to whole minutes. Working by hand from the displayed minutes gives the same results to within one minute (for example 13°53½' instead of 13°54' for the Moon); the how-to page shows that version.

Notice how the composite Sun lands in Gemini, a sign neither person's Sun is in. That is normal. A's Sun near the end of Pisces and B's Sun in Leo are 136° apart, and the shorter arc between them runs through Aries and Taurus, so the halfway point falls in early Gemini.

Why a composite can show a sky that never happened

Because each composite planet is calculated on its own, the composite does not have to obey the limits of the real sky. Seen from Earth, Mercury never strays more than about 28° from the Sun, and Venus never more than about 47°. A composite can break those limits.

A and B show it clearly. A's Mercury is at 27°16' Aquarius and B's at 6°01' Virgo, 171°15' apart. The shorter-arc midpoint is 1°39' Sagittarius, while the composite Sun is at 2°05' Gemini, so composite Mercury is opposite the composite Sun, less than half a degree from exact. The alternative midpoint for Mercury, on the other arc, is 1°39' Gemini, right beside the Sun. Which one you get depends on the midpoint convention, not on anything in either person's chart. Treat a composite Sun-Mercury opposition as a product of the convention and say which convention you used; it is not evidence that one convention is the better one.

The Davison chart: a different relationship chart

A second kind of relationship chart is often confused with the composite. A Davison chart, named after the astrologer Ronald C. Davison, who described it in his book Synastry (1977), is an ordinary chart cast for a real moment and place: the moment halfway between the two births, at a place halfway between the two birthplaces. Because it is a real sky, its planets keep their real relationships to each other. There is more than one version of the Davison chart: astrologers differ on how the halfway moment and place should be worked out, and the versions can give somewhat different positions.

The two methods can give very different charts for the same pair. The comparison below uses one variant only, the uncorrected (arithmetic-mean) Davison relationship chart: the moment halfway between the two births in Universal Time, with the plain average of the two birthplaces' latitudes and longitudes. For A and B, that moment falls in late May 1989. Other Davison variants would not necessarily match these figures exactly:

Most planets land within about three degrees of each other, and the Sun, Jupiter and Pluto within one. Mercury and Mars do not. The Davison Mercury sits next to the Sun, as a real Mercury must, while the composite Mercury is opposite it; and Mars is in Pisces in the composite but in Cancer in this Davison chart, more than 120° away. Both are established methods, and astrologers disagree about how to use them. These articles work only with the midpoint composite and do not cover how to cast a Davison chart, its angles or its houses.

How astrologers read a composite

A composite is read much like a birth chart, with the relationship in place of a person. Each planet keeps its usual meaning, now applied to what the two people share:

• Composite Sun: what the relationship tends to be about, its central purpose or shared focus.
• Composite Moon: the emotional climate between the two people, what makes the relationship feel safe or settled.
• Composite Mercury: how the pair talk, plan and think things through together.
• Composite Venus: shared values, enjoyment and the way affection tends to be expressed between them.
• Composite Mars: how the pair take action together and handle friction.

Then come the aspects between the composite planets, measured with the five major aspects. These articles use 8° for the conjunction, square, trine and opposition and 6° for the sextile, the same convention as the synastry guides. Those are the orbs the Astrologist.com calculator uses inside one natal chart; here they are only the convention for educational examples and are not composite orbs the software applies. Many astrologers work with tighter orbs in composites.

For A and B, a reading might start like this:

• The composite Sun, Venus and Jupiter are all in Gemini, with Venus conjunct Jupiter about 1.3° apart. An astrologer might read conversation, curiosity and a generous, sociable tone as themes the pair could recognise.
• The composite Moon at 13°54' Capricorn is conjunct composite Saturn (2.6°) and Neptune (2.7°) and sextile Mars (0.02°) and Pluto (0.2°). That could be read as an emotional climate that values steadiness and reliability, alongside a quieter, harder-to-define layer.
• Composite Mars is square Jupiter, almost exact, and trine Pluto. Shared drive and enthusiasm are emphasised, with the square suggesting a pull between doing a lot and doing it carefully.
• Composite Sun opposite Mercury, as explained above, comes from the midpoint convention.

These are tendencies to talk about, not facts about A and B, and certainly not a forecast. A composite does not say whether a relationship will last, whether two people will marry, stay faithful, separate, have children or do well with money, and no composite placement marks a soulmate or a fated bond. It offers a shared vocabulary for patterns two people may already notice.

Generational contacts

People born a few years apart share roughly the same Saturn, Uranus, Neptune and Pluto, and their composite repeats that. For A and B, composite Saturn is conjunct composite Neptune within 0.1°, Saturn conjunct Uranus within 7.7° and Uranus conjunct Neptune within 7.6°. Each person already has Saturn, Uranus and Neptune together in Capricorn, as do many people born in those years. Composite Pluto at 13°40' Scorpio is simply the midpoint of two Plutos less than 3° apart. These contacts describe a shared generation more than a personal bond, so they deserve little weight in reading this particular relationship.

Angles, houses and birth time

A composite can also have an Ascendant, a Midheaven and houses, and some astrologers give them a lot of weight. There is more than one way to find them, and the methods can give different answers. All of them need precise birth times for both people, because the angles of each birth chart move on average about a degree every four minutes. Astrologist.com does not show the Ascendant or Midheaven degrees needed for this, and these articles do not calculate composite angles or houses.

Without a birth time, the composite Moon is uncertain too, although by only half as much as the untimed person's Moon, because a midpoint moves half as far as the end that moves. The how-to article shows how to check whether a composite Moon contact holds across a whole birth date. Noon is never treated as a birth time; the free chart's noon Moon is only a date reference. The general limits are in what your chart can show without a birth time.

Not just for couples

The technique works for any two people: partners, friends, siblings, a parent and child, business partners or collaborators. The reading changes with the relationship: a composite Venus says something different about co-founders than about a couple. Whatever the relationship, birth data is personal, so build a composite with the consent of the other person.

A brief history

Midpoint composites were set out in English by the astrologer John Townley in the early 1970s and became widely known through Robert Hand's book Planets in Composite (1975). The Davison chart followed with Ronald C. Davison's Synastry (1977).

Where to go next

• To work out a composite for yourself, follow how to calculate a composite chart.
• To compare the two charts contact by contact instead, start with synastry basics.
• For one person's planets in the other person's houses, see synastry house overlays; composite houses are a different construct.

Related articles

• How to Calculate a Composite Chart
• Synastry Basics
• Comparing Two Charts by Degree
• Astrology Compatibility Overview
• Major Aspects
• Aspect Orbs
• All compatibility guides