Synastry & Compatibility Calculator — Free

What synastry reveals

Synastry is the astrology of relationships. Instead of one chart, it lays two charts over each other and measures the aspects — the angles — between your planets and theirs. Those angles are the real chemistry: where you flow, where you spark, and where the friction that keeps things interesting lives. It works for lovers, friends, family and colleagues alike.

The aspects that matter most

This calculator focuses on the personal planets — Sun, Moon, Mercury, Venus and Mars — because they describe who you are day to day. A trine or sextile between them feels easy and supportive; a conjunction fuses your energies; a square or opposition creates the tension that fuels attraction and growth. No aspect is "bad" — the mix is what makes a relationship real.

Your compatibility score

The score at the top is a quick read on the density and tone of the contacts between your charts — more close aspects, and more flowing ones, lift it. Treat it as a conversation-starter, not a verdict: the individual aspects below tell the real story of how two people fit together.

Go deeper

Read the full meaning of your connection in the Love Compatibility & Synastry collection, or build the shared chart of your relationship with the composite chart calculator.

Reading a square without fearing it

It's tempting to see a square or opposition in your synastry and brace for trouble, but tension in a chart comparison isn't a warning sign — it's information. A Venus square Mars, for instance, often shows up in relationships with real chemistry: the friction that makes two people notice each other in the first place. What matters more than the aspect itself is how both people handle the pull. A hard aspect asks you to negotiate — around pace, around affection, around who leads and who follows — and couples who do that consciously often build more resilient bonds than those with an entirely easy chart. Think of squares as the places where growth is required, and oppositions as the places where you complete something in each other that you don't have alone. Neither is a verdict on whether a relationship will work; they're simply where the real conversations happen, and where two people either learn each other or avoid each other.

Why the sun sign never tells the full story

Pop astrology reduces compatibility to two sun signs, and it's easy to see why — it's the simplest question to answer. But the Sun is only one placement among many, and it mostly describes your core identity rather than how you actually relate day to day. Two Aries suns can be wildly incompatible if their Moons or Venuses clash, while a Cancer and an Aquarius — a pairing sun-sign guides often call an unlikely match — can have a genuinely easy bond if their Venus and Mars line up well. Synastry looks at the whole cast: Moon to Moon for emotional rhythm, Venus to Mars for chemistry and desire, Mercury to Mercury for how you argue and joke, and Ascendant to Ascendant for how you come across to one another in daily life. That's why two people with "incompatible" signs can feel effortless together, and two people with "perfect" signs can still struggle — the sun sign is the headline, not the story. If you want a fuller picture of attraction specifically, look at where your Venus sits in your chart and compare it to your partner's Mars; that single contact often explains more about chemistry than the sun signs ever could, and it's a good next placement to study once you've run this calculator.

Frequently asked questions