Synastry: natal chart compatibility

What synastry is

Synastry is one of the oldest methods of relationship astrology. The idea is simple: take two natal charts and compare the planets of one against the planets and houses of the other. If you want to understand what a natal chart is in the first place, start with what is a natal chart.

Unlike generic sun-sign compatibility, synastry accounts for the exact position of every planet, house, and aspect at the moment of each partner's birth, giving a far more detailed and individual picture.

Reading inter-chart aspects

An inter-chart aspect is the angle between one person's planet and another's. The math is the same as in a regular natal chart: conjunction (0°), sextile (60°), square (90°), trine (120°), and opposition (180°) — except now the two points belong to different people.

Soft vs. tense aspects

Trines and sextiles between charts usually feel like ease, natural understanding, and comfort. Squares and oppositions create tension and attraction at the same time — they are often responsible for strong passion, but also for friction that requires growth and compromise.

Conjunctions — amplifying a theme

A conjunction in synastry means one planet's theme fully merges with the other's. For instance, a conjunction between personal planets and a partner's Jupiter often feels like support and optimism, while a conjunction with Pluto can feel like an obsessive pull and transformation through the relationship.

Planet overlays into a partner's houses

Beyond planet-to-planet aspects, synastry looks at which house of the partner each planet falls into. This overlay shows which area of life the partner's energy activates. A planet landing in an angular house (1, 4, 7, 10) is felt especially strongly.

For example, if one person's Sun falls into the other's 7th house, the partner is often perceived as a significant figure for marriage and open partnerships. Moon in the 4th house creates a sense of home and emotional safety. Mars in the 6th house can add energy to shared work and daily routines — but may also become a source of friction over everyday habits.

Sun and Moon: the emotional core of a couple

Aspects between partners' Sun and Moon are one of the first things checked in synastry. They show how smoothly one person's conscious identity meshes with the other's emotional needs. A detailed breakdown of these connections is available in Sun-Moon aspects.

A harmonious trine or sextile between Sun and Moon is often described as feeling "at home" with a partner. A square or opposition creates a more complex dynamic: strong attraction, but requiring conscious work to understand temperament differences.

Venus and Mars: attraction and passion

The Venus-Mars link governs romantic and sexual attraction between partners. One person's Venus in conjunction or trine with the other's Mars usually creates natural physical and aesthetic attraction. Read more about Venus placements in Venus in the houses.

Tense Venus-Mars aspects — square or opposition — aren't necessarily bad: they often add passion and excitement, but require careful attention to differing tastes and pace of intimacy.

Saturn: the test of durability

Saturn in synastry symbolizes commitment, responsibility, and time. Aspects from one partner's Saturn to the other's personal planets (Sun, Moon, Venus) often indicate seriousness of intent and long-term potential, though at first they may feel like distance or reserve.

Hard Saturn aspects can bring a sense of restriction or criticism, but when handled consciously, they are exactly what helps a couple build a stable structure and mutual responsibility — something that relationships built solely on easy aspects often lack.

Composite vs. synastry: what's the difference

Synastry compares two separate charts, remaining an "outside view" of the couple. A composite chart works differently: for each planet, a midpoint is calculated between its position for both partners, and these midpoints form a single new chart representing the relationship itself as a separate entity.

Synastry shows well how partners influence each other individually, while a composite shows what the relationship is like in itself, independent of each partner's personality. For a full picture, astrologers usually use both methods together.

Check compatibility in your own chart

Calculate your natal chart and compare it with your partner's, or check the lunar calendar for today to pick a favorable moment for an important conversation.

Frequently asked questions