A composite chart and a Davison chart are two ways of drawing one chart for a relationship. The composite takes the halfway point between each pair of planets in the two birth charts. The Davison chart is a real sky, cast for the moment exactly halfway between the two births, at a place between the two birthplaces. Enter both sets of birth details and the tool draws both charts, with every position, the aspects inside each chart and the working.
How it works
The composite chart. For each planet, the Moon’s node and, when both birth times are known, the Ascendant, the Midheaven and each house cusp, the tool takes the halfway point between the two people’s positions on the shorter of the two arcs between them, called the nearer midpoint. A Sun at 10° Aries and a Sun at 20° Gemini, for example, give a composite Sun at 15° Taurus. John Townley published the first book on the method, The Composite Chart, in 1973, and Robert Hand’s Planets in Composite made it widely known. Working out the angles and cusps as halfway points too is what Astrodienst calls the midpoint method.
The Davison chart. Ronald Davison, in his book Synastry: Understanding Human Relations Through Astrology, took the moment halfway between the two births and the average of the two latitudes and of the two longitudes, and cast an ordinary chart there. The tool does the same, with Placidus houses. You can also choose the point halfway along the shortest route between the two birthplaces instead of the plain average.
Each birth time is turned into universal time with the time zone and daylight saving in force at that place on that date. The planets are tropical positions from NASA JPL DE440 data, the node is the mean node, and the aspects inside each chart use the same orbs as our birth chart tool. Births from 1900 to 2074 are covered.
Reading the result
Astrologers read the composite chart as the relationship’s own chart: the composite Sun for what the relationship is about, the composite Moon for how it feels day to day, and the composite Ascendant for how the pair comes across together. The Davison chart is read the same way, but it is a chart of a real moment, so its planets keep the spacing they have in any sky.
Two things are worth knowing when you read a composite. Halfway points do not have to keep the rules of a real sky: in our NASA data Mercury is never more than about 28 degrees from the Sun and Venus never more than about 47, but a composite Mercury or Venus can land much farther away. When that happens the tool says so and shows the other halfway point, on the far side of the circle. And when two positions are almost opposite in the two charts (more than 178 degrees apart), the halfway point on the other side is nearly as close, and a change in one birth time could swap the two. How big a change depends on the point and on how close to opposite the two positions are. The Ascendant and Midheaven go round the zodiac once a day, so for them it is a matter of minutes. The Moon goes round in about 27 days and never moves less than about 12 degrees a day, so for it the change is at most about four hours. The Sun, Mercury, Venus and Mars take one to two years on average to go round, so it is usually hours or days, and for Jupiter, the slower planets and the node it is usually days to weeks, sometimes months. The tool flags each such point and works out how much one birth time would have to change to swap it.
The Davison date often falls years away from either birthday. With ten years between two births, it falls five years after the older person’s birth.
Where traditions differ
Composite houses are drawn in two main ways. The midpoint method, used here, takes every cusp as a halfway point. The reference place method takes only the composite Midheaven that way and then works out the Ascendant and houses for the latitude of a chosen place, such as where the couple live. The two give the same planets but can give different houses.
For the Davison chart, Davison averaged the latitudes and longitudes. Others take the point halfway along the shortest route between the two birthplaces, which can be very different when the places are far apart, especially on opposite sides of the date line; the tool offers both. Some programs also nudge the Davison time so that its Midheaven matches the composite Midheaven; this tool keeps the exact halfway moment.
What it does not do
It gives no score and makes no forecast for the relationship. It does not compare one person’s planets with the other’s; that is synastry, and our synastry calculator does it. Without a birth time for either person it leaves out the Ascendant, Midheaven and houses, and treats the Moon as approximate. It does not draw the reference place version of the composite or progress either chart.
Frequently asked questions
↳ What is the difference between a composite and a Davison chart?
The composite is made of halfway points between the two birth charts, so it is not the sky of any real moment. The Davison chart is the real sky at the moment halfway between the two births, seen from a place between the two birthplaces.
↳ Why is the composite Venus so far from the Sun?
Each composite point is a halfway point worked out on its own, so the planets do not have to keep their usual spacing. When Mercury or Venus ends up farther from the composite Sun than it can ever be in a real sky, the tool says so and shows the other halfway point as well.
↳ Do we both need a birth time?
For the full charts, yes. Without a time the tool uses 12:00 local time, so the planets are still close but the Moon can be several degrees out, and the Ascendant, Midheaven and houses are left out.
↳ Which place should the Davison chart use?
Davison used the average of the two latitudes and longitudes, and that is the default. If you were born far apart, try the shortest route option too and compare; only the Ascendant, Midheaven and houses change.
↳ Is this a compatibility score?
No. Both charts describe a relationship as a whole, in the language of signs, houses and aspects. Astrology offers themes to talk about, not a verdict on whether a relationship will work.
↳ Why is the Davison chart dated years after my birthday?
It is cast for the moment halfway between the two births. With an age gap of ten years, that moment falls five years after the older person was born.