Birth chart compatibility
calculator — free, by date of birth
The compatibility calculator by date of birth: we overlay your birth chart and your partner’s, and show where your energies attract, complement — or rub against each other. Free, with an interpretation for every link, and far more than just sun signs.
Compare your two birth charts and see how well you click — in love, everyday life and on a soul level.
Person 1 — you
When were you born?
The date sets the Sun, Moon and every planet.
Three steps to a compatibility chart
Enter both birth data sets
Date, time and place for you and your partner. The more precise the times, the more detailed the read — especially for Ascendants and houses.
Compute the synastry
We overlay both charts and calculate every aspect between your planets. The result: a map of the energetic touch-points between you.
Read your connection
Every aspect gets a clear interpretation — what it typically creates between two people, where your strengths are, what you can work on.
The basics
How well do you match?
A compatibility check compares your two birth charts to see how your energies fit together — where you naturally click, and where you’ll need a little patience. It’s the astrology behind that feeling of "we just get each other" (or "why do we keep having the same argument?").
There are no "bad" matches
Every pairing has easy spots and growth spots — even the most harmonious one. Challenging connections aren’t a red flag; they’re often where a relationship grows the most. A compatibility check shows you both, so you know what comes naturally and what’s worth working on together.
What matters most
A few connections carry the most weight: your Suns (your core selves), your Moons (how you feel and comfort each other), your Venus (how you love and show affection) and your Mars (desire and how you handle friction). When these fit well, everyday life together feels easy.
Birth chart compatibility: what gets compared
A compatibility reading needs two birth charts. The calculator lays them on top of each other and measures the angle between you for every planet pair: your Venus to their Mars, your Moon to their Sun. The date of birth covers the Sun, the Moon (usually), Venus and Mars. Birth time and place complete the picture, because only then are the Ascendant and the houses fixed.
| Link | What it shows | What you need |
|---|---|---|
| Sun × Sun | whether your basic direction fits | Date of birth |
| Moon × Moon | how you comfort each other and what calms you | Date, better with time |
| Venus × Mars | attraction — who wants whom, and how | Date of birth |
| Mercury × Mercury | how you talk, argue and make up | Date of birth |
| Saturn × personal planets | commitment and staying power | Date of birth |
| Ascendant and houses | how you come across as a couple — in the composite part of the result | Time and place |
The five angles the calculator measures
- Conjunction (0°) — both sit in the same spot and act as one force.
- Sextile (60°) — an open offer — it helps when you take it up.
- Square (90°) — friction that pushes you to act.
- Trine (120°) — the two work together without you having to do anything.
- Opposition (180°) — two poles looking for a balance.
How a single angle feels is explained on the aspect pages, for example Venus square Mars, the classic spark-and-friction aspect. A scene from everyday life: you plan a weekend, one of you wants to just go, the other wants it booked first. If a square links Mars and Mercury between you, that is not chance — it is a pattern you can recognise and name.
How to read your result
- Start with the tightest links — the smaller the distance to the exact angle, the more you feel it.
- Read flowing and demanding links together. A trine explains what runs easily, a square what you keep talking about.
- Check every statement against a real situation from last week. Whatever does not fit, you can cross out.
Only know your star signs? The quick zodiac sign comparison is enough. To see the couple as its own entity, build the composite chart — a third horoscope made from the midpoints of your two.
Compatibility — frequently asked questions
- How does a compatibility calculator by date of birth work?
- Enter both dates of birth above — plus, if you can, birth times and places. The calculator builds two full birth charts, overlays them and interprets every link between your planets. You get the result instantly, free, no sign-up.
- How is this different from a simple zodiac-sign match?
- Your zodiac sign is only the position of the Sun — one point of many. A calculator that works from the date of birth also compares Moon, Venus, Mars, Mercury and the slow planets. That is why two "incompatible" sun signs can be a wonderful match: the rest of their charts tells a different story.
- Does the compatibility chart tell me whether we fit?
- Not in a yes-no sense. It shows where your connection lives, where it needs work, and which themes typically come up between you. Whether you fit is decided by your shared story — the chart hands you the map.
- Do I need my partner’s exact birth time?
- For the most important links (Sun, Moon, Venus, Mars), date and place are enough. For a full analysis with Ascendant and house connections the time matters. Without a time we still calculate — just without the Ascendant layer.
- Does this work for friendships or family too?
- Yes. The comparison works for any relationship between two people — romantic partners, best friends, siblings, parent and child. The links are the same; what you read out of them differs.
- What is a “good” result — and what does the score mean?
- There is no pass or fail. The score sums up how easily your energies find each other — but a mix of harmony and tension usually lasts better than pure harmony. Too much harmony can fall asleep, too much tension exhausts. What matters is what you make of both.
Your connection, in four layers
Emotional compatibility
How do your Moons meet? How do your Venuses fit? The emotional layer is usually what carries a connection — or exhausts it.
Mental compatibility
Mercury to Mercury, Ascendants in contact — how you think, speak, argue. Where your thoughts meet, and where you talk past each other.
Attraction and tension
Which aspects between your Mars, Venus, Sun and Moon positions create attraction, which create friction? Both are part of any alive relationship.
Long-term composition
What happens when the slow planets meet? Saturn and Jupiter between your charts show whether the connection has depth and stamina.
More calculators & tools
Big Three comparison
Sun, Moon and Rising — the quick three-level comparison.
Venus & Mars calculator
How you love and what drives you — date of birth only.
Zodiac sign compatibility
Pick two signs, see the result instantly — no birth data at all.
Birth chart
Your own chart as the foundation for synastry.
Daily transits
What today’s sky is saying about your connection.
Solar return
Your own astrology year, starting on your birthday.
Astrology events
Eclipses, ingresses, retrogrades — on the calendar.
All instruments
The astrology hub with all five tools.
Learn astrology & tarot
Read synastry and tarot yourself in 30 days, step by step.
Reviewed by Katie Robinson · Astrologer & Tarot ReaderReady to overlay your charts?
Two charts, every aspect, a complete synastry — free, with an interpretation for every link.
Start the compatibility chartFree, no sign-up.