Synastry Calculator

How Synastry Works: Two Charts, One Overlay

Synastry does not create a new chart. It places both natal wheels side by side and calculates the angular relationships (aspects) that form between Person A's planets and Person B's planets. These inter-aspects are distinct from each person's internal chart dynamics. A square between your natal Moon and your partner's Saturn, for example, is an inter-aspect that only exists in the context of your relationship. The analysis spans all ten classical planets plus the lunar nodes and the major angles (Ascendant, Midheaven) when accurate birth times are provided. The result is a layered portrait of compatibility that no single planet or aspect can summarize alone.

Key Synastry Aspects to Watch

Certain inter-aspects carry particular weight in relationship analysis. Sun conjunct or trine Moon between partners signals deep complementarity: one person's core identity harmonizes with the other's emotional nature. Venus conjunct or sextile Mars is the classic attraction signature, pointing to physical and romantic chemistry. Moon conjunct Moon or Moon in the same sign suggests instinctive emotional attunement and shared domestic rhythms. Saturn aspects to personal planets (Sun, Moon, Venus) introduce themes of commitment, responsibility, and sometimes restriction: these bonds tend toward longevity but require conscious effort. Pluto inter-aspects (especially conjunctions to the Moon or Venus) signal intensity, transformation, and a relationship that fundamentally changes both people.

Inter-House Overlays: Where You Land in Each Other's Lives

Beyond aspects, synastry reads inter-house overlays: the houses of Person B's chart where Person A's planets fall. If your Venus lands in your partner's seventh house, you naturally embody partnership and beauty in their life. If your Saturn falls in their fourth house, you may become a structuring or stabilizing force in their domestic world. Inter-house overlays explain why certain people feel instantly significant in a specific life domain, even before a relationship fully develops. This layer of synastry requires accurate birth times for both individuals, because house positions shift roughly one degree every four minutes.

The Lunar Nodes and Karmic Dimensions

The lunar nodes (North Node and South Node) occupy a special place in synastry because they point to the evolutionary and karmic dimension of a bond. When one person's personal planet, especially the Sun, Moon, or Venus, conjuncts the other's North Node, astrologers interpret this as a forward-moving contact: the planet person helps the Node person grow toward their soul's direction. South Node conjunctions feel intensely familiar, as if you have known each other before, but they can also pull both partners toward comfortable old patterns rather than growth. Node contacts do not require precise birth times since the nodes move only about three minutes of arc per day.

Synastry vs. Composite Chart: Two Different Questions

Synastry and the composite chart are complementary but distinct tools. Synastry keeps both charts separate and examines how two individuals interact: it answers the question, what happens between these two people? The composite chart, by contrast, calculates the midpoint of each planetary pair (your Sun and their Sun, your Moon and their Moon, and so on) to produce a single merged chart representing the relationship as its own entity. Think of synastry as the chemistry between two people and the composite as the personality of the relationship itself. Most astrologers read both before drawing conclusions about long-term compatibility or timing.

Frequently asked questions

What is synastry in astrology?

Synastry is the astrological practice of comparing two natal charts by overlaying them and analyzing the inter-aspects (angular relationships) formed between one person's planets and the other's. It maps how two individuals affect each other emotionally, romantically, intellectually, and spiritually, producing a relationship-specific portrait that neither chart contains alone.

Which synastry aspects indicate soulmates?

No single aspect defines a soulmate, but several contacts recur in bonds that feel fated or deeply transformative: Sun conjunct Moon (identity meets emotion), Venus conjunct or trine Mars (attraction and desire), personal planets conjunct the North or South Node (karmic resonance), and Pluto conjunct Venus or Moon (profound, life-altering intensity). A cluster of these contacts across both charts carries more weight than any one aspect in isolation.

What is the difference between synastry and the composite chart?

Synastry keeps both natal charts separate and reads the inter-aspects between them, showing how two individuals interact with each other. The composite chart calculates midpoints between each planetary pair to create a single merged chart that represents the relationship itself as an entity. Synastry answers how do these two people affect each other, while the composite chart answers what kind of relationship is this.

Do I need birth times for synastry?

Accurate birth times are strongly recommended for both people. Without them, house positions and the Ascendant cannot be calculated, eliminating inter-house overlays and angular aspects to the Ascendant and Midheaven. Planet-to-planet inter-aspects remain valid without exact times, but the analysis loses a significant layer of precision. The Moon also moves roughly 12 to 13 degrees per day, so an uncertain birth time can place it in the wrong sign.