How to use this tool
Enter each person’s details separately. The gold ring represents person A and the teal ring represents person B. Read the cross-chart aspect list and select a planet for a clearer view.
✧ TWO SKIES, ONE CONVERSATION
Synastry chart
Compare two birth charts. Explore planetary connections without reducing a relationship to a score.
◈ Free, no account◈ Calculated on your device
Every sky has a starting point.
Add your details to see the calculation and explore its meaning.
✧ Real positions. Room for reflection.
A FIELD GUIDE
A little context for your sky
What the result means
Synastry compares the longitudes of planets in two natal charts. Traditional readings consider ease, contrast and recurring patterns. Good relationships still depend on communication, consent and everyday choices—not chart geometry.
How we calculate
Astronomy Engine calculates geocentric positions in the tropical zodiac. Birth times are converted using a bundled IANA time-zone database. House geometry and aspect rules are computed separately. Supported input dates are 1900–2100.
Read the methods, limits and sources →Questions you might have
Can I compare two birth charts for free?
Yes. No account is required, and the entered birth details are calculated in your browser.
What if I do not know the other person’s birth time?
Mark that person’s time as unknown. We omit their houses and Ascendant and show the uncertainty around the Moon.