Free Synastry & Compatibility Calculator

Synastry compares two birth charts to reveal the chemistry between you — where you click, where you clash, and what pulls you together. Enter both sets of birth details, then ask our AI about the connection.

Swiss Ephemeris precisionBoth charts computed for the exact moment and place of each birth — the astronomical standard professional astrologers use.
No birth time? Still worksWithout a time the chart is cast for noon and only what holds all day is used — no invented Ascendant, no invented houses.
Free & privateNo account and no card. Neither person’s details are ever shared with anyone.

Here for love itself? Love Synastry reads the two of you only as a couple — attraction, how each of you loves, desire, closeness and the year ahead for your bond. Go to Love Synastry →

You

Name *

* Your book speaks to you by name — write the name you like to be called. We never share it with anyone.

Date of birth

YYYY

Time of birth

Time not known — the chart is cast for noon; the book leaves out the Ascendant and the houses, and keeps only what holds all day.

Gender

Male

Female

For the grammar of the book only.

Place of birth

The other person

Name *

The book names the other person by this name.

Date of birth

YYYY

Time of birth

Time not known — the chart is cast for noon; the book leaves out the Ascendant and the houses, and keeps only what holds all day.

Gender

Male

Female

For the grammar of the book only.

Place of birth

We need your email to send you a preview of your synastry book. We never share it with anyone.

Website

Your preview is being prepared

These pages are from your own book. The chapters are written when you order.

What you get

Fill in both people once — your comparison opens on its own page, yours to come back to.

1Both charts, side by side

Each birth chart drawn from its exact moment, and the two laid over each other in one wheel.

2Every contact between you

Which planet of one touches which planet of the other, with the exact orb — and where each of you lands in the other’s houses.

3Your pair in numbers

Feelings, talk, values, drive and what you build — two bars for each question, one for each of you, never a single love score.

4Your synastry book, if you want it

A free preview first. The book itself is 60+ pages on the two of you, in your language. Optional — the comparison is free.

Ask AstroNoir AiChat About the Two of You

Ask our AI up to three free questions about your synastry — it reads both birth charts and the contacts between them.

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What synastry is

Synastry lays two birth charts over each other and measures the cross-aspects — the precise angles each person's planets make to the other's. The kind of angle is everything. A trine or sextile is easy flow: those parts of you support and understand each other almost without effort. A square or opposition is friction — the places you rub, challenge and grow each other, and very often exactly where the attraction lives. A conjunction blends two planets into one charged point, intensifying whatever they touch. Stack up all these contacts and you have the living dynamic between two people — not a verdict, but a map. AstroNoir computes both charts and every major cross-aspect with Swiss Ephemeris precision, the arc-second planetary data professional astrologers rely on.

What your compatibility really means

No single chart contact makes or breaks a relationship. Easy aspects flow, but on their own they can leave a bond comfortable and a little inert; hard aspects bring tension, yet they are also the spark, the charge and the reason two people keep growing toward each other. The couples who last are rarely the ones with the smoothest synastry — they are the ones who understand their friction and work with it on purpose. Real compatibility is what two people do with their chart contacts, not the contacts themselves. Read this as a mirror for the dynamic, never as a verdict on the future.

Synastry shows how your planets touch each other. To see the relationship as its own entity — its purpose, character and direction — build your composite chart. The two readings answer different questions and are strongest side by side.

Frequently Asked

What is synastry?

Synastry is the branch of astrology that compares two birth charts to understand a relationship — the aspects between your planets show where you harmonize and where you challenge each other.

Do we both need birth times?

Birth times sharpen the picture, but you can still get a meaningful planet-to-planet synastry without them. Exact times fix three things: the Moon (which moves about half a degree an hour), the Ascendant (which changes sign roughly every two hours) and all the houses. Without a time we fall back to a noon chart, so the planet-to-planet aspects stay reliable while the Moon may be slightly off and the Ascendant and house overlays cannot be trusted. For the full picture, an accurate time for both people is best.

What is the difference between synastry and a composite chart?

Synastry compares your two separate charts — your planets to theirs. A composite merges both into one new chart of the relationship itself. Synastry shows the chemistry between you; the composite shows what the relationship is. They answer different questions and are strongest read together.

Which synastry aspects matter most?

Contacts between the personal points carry the most weight: Sun-Moon for understanding, Venus-Mars for attraction, Moon-Moon for emotional rhythm, and Ascendant contacts for instant chemistry. Saturn contacts add staying power and sometimes weight, while outer-planet contacts bring intensity and transformation.

Does synastry say if we are compatible?

It describes the dynamic, not a verdict. Easy aspects flow; hard aspects bring growth and spark. Real compatibility is what two people do with their chart contacts — the same synastry can build a lasting bond or a brief one, depending on awareness and effort.

Can synastry tell us if we will last?

No reading can predict that, and we never would. Synastry shows the raw material — where you flow, where you stretch each other, what you will have to navigate. Whether it lasts is up to the two of you, not the chart.

Is it free?

Yes, completely free, with no account required.