Synastry Calculator
A synastry calculator takes two birth charts and lays them over each other, so you can see exactly how your planets meet someone else's. It's the fastest way to turn two sets of birth details into one relationship chart — the aspects, the overlaps, the friction and the ease. Enter both people's details below and yours builds in a couple of minutes.
Calculate Your Synastry Chart
Enter both people's birth details below and the calculator will build your synastry chart. For each person you'll need three things: their birth date, their birth time, and their birth place.
That's two full sets of details — one for you and one for the other person — because synastry is a comparison. The calculator pins down each person's planets from their own birth data, then measures the angles between the two charts to find the aspects that describe the relationship.
Once your chart loads, you'll see both sets of planets on a single wheel, with the aspects between them mapped out and ready to read.
Person 1
Person 2
Enter birth date and place for both people to continue. Birth time is optional.
By continuing you confirm you are at least 16 years old (or have your parent or guardian's permission) and agree to our Terms and Privacy Policy. Astrological readings are AI-generated for entertainment and self-reflection — they are not professional advice. See our Disclaimer.
How the Synastry Calculator Works
The calculator builds each person's natal chart from their birth details, then overlays the two and measures the aspects — the angles one person's planets make to the other's. Those cross-chart aspects are what turn two separate charts into a single relationship map.
Here's what you give it and what you get back:
- Both birth dates, times, and places. One set for each person. The dates and places fix where every planet sat, and the times set the houses and the rising signs.
- Your synastry chart. A combined wheel showing both people's planets, the houses each person's planets fall into on the other's chart, and the aspects between the two.
- The cross-chart aspects. Conjunctions, trines, squares, and oppositions between your planets and theirs — the contacts that show where the relationship flows and where it pulls.
Exact birth times for both people make the reading far more accurate, since the houses and the Moon shift through the day. If one time is missing you can still generate a chart — just treat the house overlays and the Moon's position as approximate.
What Your Synastry Chart Shows
A synastry chart shows how two people's planets interact — where they support each other, where they clash, and which areas of life light up between them. The aspects between the charts carry most of the story: easy aspects tend to feel smooth, hard aspects bring tension and attraction, and the planets involved hint at what the connection is really about.
This page is built to generate the chart, not to walk through every aspect. For the full picture of what synastry is and how the pieces fit together, start with our synastry chart guide. When you're ready to read your own chart line by line, our guide to what your synastry chart means takes it aspect by aspect.