Composite chart calculator

What a composite chart is

A composite chart blends two birth charts into one. For every planet, it takes the point exactly halfway between where that planet was in the first chart and where it was in the second. Your Sun at 10 degrees Aries and a partner's Sun at 20 degrees Gemini give a composite Sun at 15 degrees Taurus.

Astrologers read the result as the birth chart of the relationship: a third character with its own temperament, needs and way of showing itself, separate from either person. Where synastry asks how two people meet each other, the composite asks what the two of them make together.

How the midpoints are found

Every pair of positions has two midpoints, one on each side of the zodiac. The composite uses the nearer one, on the shorter arc between the two planets. When two planets sit almost exactly opposite each other, more than 175 degrees apart, the nearer midpoint becomes unstable and a small change would flip it to the other side. The page flags any planet in that position and gives the other point too, because astrologers differ on which to read.

Houses need both birth times. The composite Midheaven is the midpoint of the two Midheavens; the houses are then drawn from it at the average of the two birth latitudes, which is the most common way programs build composite houses. Other programs average the house cusps one by one, so their composite houses can differ a little.

How to read your composite chart

• The composite Sun is read as the purpose of the relationship: what it is for and what it shines at.
• The composite Moon is read as its emotional climate: what makes the two of you feel safe together.
• Venus and Mars describe the relationship's affection and its drive, including how it handles conflict.
• The composite Ascendant, with both birth times, is how the couple comes across to friends and family.
• The house of each planet shows the area of shared life where that theme plays out.

The readings under the chart are our birth chart readings of each placement. Astrologers apply them to the relationship as if it were a person, so read "you" as "the two of you together".

The composite relocation map

This is the first free composite chart that also draws its lines on the world map. A composite planet's MC line marks where that planet sits on the composite Midheaven, its AC line where it sits on the composite Ascendant, and so on. Astrologers who use relationship maps read a city near the composite Venus or Jupiter line as a place where the couple's warmth or optimism comes forward, and a city near the composite Saturn line as a place that asks more of the relationship.

A composite chart has no real moment of its own, so its lines are drawn from the zodiac degrees of the midpoints (on the ecliptic) and anchored to the composite Midheaven. The marked point on the map is where the composite chart's houses are drawn. Choose a theme to list the large cities near the matching composite lines, tap any place to see its nearest lines, and compare with the Davison map, which is drawn from a real sky.

As with any astrocartography map, a line is one input among many. Practical matters come first; couples tend to use the map to pick a trip or weigh up cities they already have in mind.

Composite or Davison chart?

Both build one chart for two people. The composite averages the planets one by one; the Davison chart averages the birth moments and places, then casts a real chart for that moment. The two often share many signs, but they are not the same chart: the composite Sun is always halfway between the two Suns, while the Davison Sun is wherever the Sun really was at the midpoint date. Some astrologers prefer the composite because it comes straight from the two charts; others prefer the Davison because it is a sky that existed. Many look at both.