A composite chart is a separate chart made from two birth charts. In Western astrology, some readers use it as a symbolic way to discuss a relationship.
Match the same body in both charts
Start with the Sun in each birth chart. The composite Sun is placed halfway between those two positions. The same idea is used for the two Moon positions and each matching pair of planets.
A chart made by calculation
These middle points form a new chart. They do not record the sky at one actual moment, such as the day two people met. The chart is a symbolic construction.
How it differs from synastry
Synastry compares the two original birth charts. A composite chart instead uses the calculated middle points. You only need to remember the difference in method before reading an interpretation.
A few common questions
Can a composite chart tell me whether a relationship will last?
No. It cannot determine whether a relationship is good or bad, or whether people should stay together. Those choices depend on their wishes, actions, and how they treat each other.
Sources & further reading
Astrology sources describe their own traditions and methods; they do not establish predictive accuracy. The writing exercises are original Lodestar editorial material.