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.

Person A
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Using 12:00 — a noon-chart fallback.

No exact time? You can still read a meaningful planet-to-planet connection — only the Moon, Ascendant and houses truly need it.

Person B
DD
MM
YYYY
HH
MM

Using 12:00 — a noon-chart fallback.

No exact time? You can still read a meaningful planet-to-planet connection — only the Moon, Ascendant and houses truly need it.

No account, no sign-up · both charts are computed fresh and deleted when your session ends · the AI reads only those charts and never gives medical, legal or financial advice.

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Ask AstroNoir About Your Connection

The aspects are the map. Ask our AI up to three free questions — it reads both charts and the synastry between them.

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Your privacy. No account, no sign-up — you can enter test data and stay completely anonymous. Everything you enter is used only to compute your chart and to let the AI answer you during your visit, then automatically deleted when your session ends — we don't keep it, sell it, or tie it to your name. The AI reads only your freshly computed chart, never a stored profile, and never gives medical, legal or financial advice. The one and only thing we ever keep is fully anonymous: if our Birth Time Finder guesses your time and you choose to tell us it was wrong, we save that single correction — with no name, ever — to make our guessing better. Nothing else.

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.

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