Synastry calculator (free compatibility by birth date)

Enter two birth dates to see the Sun, Moon, Venus and Mars placements used in Western synastry and how they relate. Add birth times to include the Moon in the aspects. No signup; nothing is sent.

Launch prices until Nov 15, 2026, 23:59 JST: Standard 2,980 JPY → 2,235 JPY / Premium 5,980 JPY → 4,485 JPY

You
Partner

Without a birth time, noon is used and any body that changes sign that day shows both signs. The Moon moves about 13° a day, so it is left out of the aspect list for anyone without a time. Nothing is sent; everything runs in your browser.

What the paid PDF report includes

Standard ¥2,235 (about US$14) · launch price until Nov 15, 23:59 JST (regular ¥2,980, about US$19)

  • One analysis of your birth chart in both Western astrology and Jyotish
  • Results on screen plus 4 PDFs: Guide, Western report, Jyotish report and the Five Paths sheet

Premium ¥4,485 (about US$28) · launch price until Nov 15, 23:59 JST (regular ¥5,980, about US$38)

  • One analysis in both systems, with the first-pass analysis (L1) and the integrated interpretation (L2) kept as separate layers
  • Results on screen plus 6 PDFs: Guide, Western L1, Western L2, Jyotish L1, Jyotish L2 and the Five Paths sheet

One-time purchase for one analysis; no subscription. The PDFs are emailed to you when the analysis is complete. Prices are charged in Japanese yen (JPY). US$ amounts are approximate, based on the ECB reference rate on Nov 10, 2026; your card issuer converts at its own rate.

Start Standard or Premium ↗Compare plans and pricing →See a sample report →

For your whole chart, use GenesisCore

This tool shows one part of the chart. GenesisCore starts with a free analysis and reads character, strengths, work and timing in both Western astrology and Jyotish.

Start GenesisCore (free) ↗Is astrology science? Join the experiment ↗

How it is calculated

Positions are geocentric apparent ecliptic longitudes from Astronomy Engine (MIT); sidereal signs subtract the Lahiri ayanamsa. Checked against Swiss Ephemeris 2.10 at 60 instants between 1900 and 2100: the Sun, Venus and Mars agree within 10 arcseconds and the Moon within about 1 arcminute, with every sign and all 30 test pairs' aspect lists identical. Aspects are the conjunction, sextile, square, trine and opposition, with wider orbs when the Sun or Moon is involved.

How to read synastrySun sign vs. Moon signWestern vs. Vedic astrology

FAQ

Can I check compatibility with birth dates only?
Yes. The Sun, Venus and Mars move little in a day, so the date is enough. The Moon moves about 13° a day; without a birth time, both signs are shown if it changes sign that day, and it is left out of the aspects.
Why is there no compatibility score?
Synastry is read from which planets connect and by which aspect. The tool shows the placements and aspects as they are and explains how each is traditionally read.
What is an orb?
The distance from the exact angle. Two planets 118° apart form a trine (120°) with a 2° orb. The smaller the orb, the more exact the aspect.
Is Vedic compatibility different?
The sidereal zodiac is about 24° behind the tropical one, so signs can differ. Jyotish also uses other methods, such as Ashta Koota, which scores eight factors from the Moon nakshatras.
Are the birth dates stored?
No. Nothing is stored or sent; everything runs in your browser. Shared links contain only the two Sun and Moon signs.

More free tools

Synastry Calculator (Free) | Sun, Moon, Venus and Mars Compatibility