Composite Chart Calculator
A composite chart turns two birth charts into one by taking the midpoint between each pair of planets. Enter both birth dates, times and places to see the chart of the relationship itself, with its planets, houses and aspects.
What a composite chart is
Where synastry compares two charts, a composite chart blends them into a single chart that astrologers read as the relationship's own personality: what the two of you create together, rather than what each brings. The method was popularized in the 1970s, notably by Robert Hand's book Planets in Composite, and is now standard in astrology software.
A composite chart does not belong to a moment in time. No sky ever looked like it; it is a mathematical construction. That is the main difference from the Davison chart, which is cast for a real moment and place.
How midpoints are calculated, with an example
For each planet, the calculator takes the two natal positions and finds the point halfway between them along the shorter arc of the zodiac.
Example: one person's Sun is at 10 degrees Aries, the other's at 20 degrees Libra. Measured from 0 Aries, those are 10 and 200 degrees. Going the short way round, through Capricorn, they are 170 degrees apart and the midpoint is 285 degrees, which is 15 degrees Capricorn. The other midpoint, 15 degrees Cancer, lies on the long arc, so it is not used. When two positions are almost exactly opposite, the short and long arcs are nearly equal and a tiny change in one birth time can flip the composite planet to the opposite sign. The calculator warns you when that happens.
Houses are built the usual way for composites: the composite Midheaven is the midpoint of the two Midheavens, and the Ascendant and other cusps are derived from it for the average latitude of the two birthplaces. That is why composite houses need both birth times.
Reading a composite chart
Astrologers read the composite Sun as the relationship's central purpose, the composite Moon as its emotional climate, and composite Venus as how affection is shared. The houses show where the relationship spends its energy: a composite Sun in the fourth house, for instance, is read as a bond built around home and family life. Aspects inside the composite chart are read like natal aspects, as the relationship's built-in harmonies and tensions.
One quirk follows from the math: composite Mercury and Venus always stay near the composite Sun, just as they do in a natal chart, because each person's Mercury and Venus were near their own Sun.
Common composite chart mistakes
- Comparing it with a natal chart as if it were a birth. The composite has no date and no place; transits to it are used by some astrologers, but there is no single birth moment behind it.
- Missing birth times. Without both times, the composite Moon can be uncertain and the houses and angles cannot be drawn.
- Reading it as a verdict. A composite chart describes themes of a relationship, not whether it will last.
Which relationship chart to use
Use synastry to see how two people affect each other, the composite to see the relationship as a unit, and the Davison chart if you prefer a relationship chart cast for a real moment. Each person's own chart is in the birth chart calculator.
Questions
What is a composite chart in astrology?
A single chart made from two birth charts by taking the midpoint of each pair of planets and points. Astrologers read it as the chart of the relationship itself.
How do you calculate a composite chart?
For each planet, find the halfway point between the two natal positions along the shorter arc. The composite Midheaven is the midpoint of the two Midheavens, and the houses are derived from it. The calculator does all of this for you.
What is the difference between composite and Davison charts?
A composite chart averages positions; a Davison chart averages the two birth times and places and casts a real chart for that moment. They often look similar but can differ in signs and houses.
Do I need birth times for a composite chart?
For the houses, Ascendant and Midheaven, yes, both times. Without them you still get the composite planets, but the Moon may be uncertain.
What does the composite Sun mean?
It is read as the central purpose or identity of the relationship: what the two of you shine at together.
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