A composite chart is the chart of your relationship. Your relationship is seen as a separate entity, and gets a chart of its own. There are a few things you want to take a look at in a composite chart so you can understand the relationship better. The first thing to look at is the composite AC. The AC is the 1st house cusp, and the sign can show how the two of you come across as a couple. If the composite AC is at a critical degree, your relationship may not come across the way you want it to, or people have a hard time understanding your relationship.
Next, focus on the Sun, Moon, and Venus. As the Sun and Moon are important in a natal chart, so too are they important in the composite chart. The Sun is the identity of the relationship, and the Moon is what the relationship needs to be stable. Venus is important if this is a romantic relationship since she is the planet of love, so composite Venus can show how love is expressed in the relationship.
You should look at the 1st, 5th, and 7th houses next, not just the signs on the cusps, but also any planets in these houses. The 5th house rules love and romance, and the 7th house rules commitment. Having the Sun, Moon, Venus, Mars, or Jupiter in any of these three houses is beneficial for the relationship.
For sexual chemistry, look at the 5th and 8th houses (5th house is more playful about it, 8th house more serious and intense), as well as the relationship between composite Venus and composite Mars and their midpoint (the exact middle). Venus sextile or trine Mars makes the energy easier, while squares and oppositions make it hotter. A conjunction is major chemistry that’s almost impossible to ignore. Unless it’s in the 12th house!
The 12th house is the house of the hidden, so if any composite planets are in this house, that energy can be difficult to express in the relationship. In love relationships, it can be difficult to express your feelings and affection if the Moon or Venus are here.
Also look at what composite Jupiter and composite Saturn are doing in the chart. Happy Jupiter makes things more pleasant, but can also breed laziness. His expansive influence will be most felt in the relationship based on the house he’s in. Saturn can help create lasting commitment, and some hard aspects (conjunction, square, opposition) can be good, but you don’t want to see too many, otherwise it makes things too difficult. Saturn’s restrictive influence is felt based on the house he’s in.
In addition to looking at the composite chart itself, you can compare each of your charts to it to see how the relationship impacts each of you as individuals. We’ve all seen that relationships can be better for one person than the other, which becomes evident when you compare individual charts to the composite.
You can use the composite chart for making predictions as well, just like with your natal chart. Pay attention to aspects to the 1st, 5th, and 7th house cusps and rulers, aspects to the Sun, Moon, and Venus, and planetary movement through the composite houses. Hard aspects by Saturn, Uranus, Neptune, and Pluto can show periods of difficulty in the relationship, and if there are several at once, can show the breakup. Positive Jupiter and Saturn aspects can show committing to one another.