Synastry is the astrology of relationships, comparing two birth charts to see how two people interact. Enter both sets of birth details and this calculator finds the aspects between one person's planets and the other's, scores the overall compatibility and lists the key connections, giving a far deeper view than Sun signs alone.
How Synastry Works
Every planet in one chart can form an aspect to every planet in the other, and those cross-aspects describe the chemistry between two people. A harmonious link between one person's Venus and the other's Mars speaks of attraction, while a tense aspect between two strong planets shows where friction lives. Synastry weighs all of these together rather than reducing the pair to a single sign.
The Compatibility Score
The calculator turns the balance of flowing and challenging aspects into a score and a plain verdict, from strong compatibility down to challenging. Flowing aspects add ease and support, challenging ones add tension and growth, and the most lasting relationships usually have some of both. A high score points to natural rapport, while a lower one flags work, not failure.
Reading the Connections
Beyond the score, the listed aspects show where the connection is strongest and where it is testing, which is often more useful than the number itself. Add each person's birth time and timezone for the sharpest results, and remember that synastry describes a dynamic between two people rather than judging whether a relationship should exist.
Comparing Two People's Charts
Enter both birth dates, and add each person's time and timezone for a fuller reading. Press Calculate and the tool lays one chart over the other and scores the inter-aspects, the angles each person's planets make to the other's. The result is a relationship read built from how the two charts actually meet, not just a Sun-sign pairing.
The Contacts That Weigh Most
Not every connection between two charts counts the same. Contacts between the Sun and Moon, and between Venus and Mars, are read as the heart of attraction and ease, while hard aspects to Saturn or the outer planets show where friction or growth lives. The score sums these inter-aspects across both charts, so a high number reflects many supportive links rather than a single lucky one.
Why Both Birth Times Matter
The most personal contacts, those to each person's Moon and Ascendant, depend on having both birth times. With them, the fast points line up precisely and the reading is at its sharpest; without them, the aspects between the slower planets still hold, but the most intimate links can't be placed with confidence. Two accurate times give synastry its full depth. Even so, a strong score is an invitation to look closer, not a verdict on the relationship itself.
Synastry Questions
What is synastry?
Synastry is the comparison of two birth charts to study a relationship. It looks at the aspects between one person's planets and the other's to describe the chemistry, ease and tension between them.
How is the compatibility score worked out?
The calculator weighs the flowing aspects, such as trines and sextiles, against the challenging ones, such as squares and oppositions, between the two charts, and turns the balance into a score and a verdict.
Do challenging aspects mean a bad match?
No. Challenging aspects add tension and growth, and most lasting relationships contain a mix of easy and hard links. The aspect list shows where the strengths and the work lie, which matters more than the score alone.
Positions are computed with the Swiss Ephemeris. Astrological interpretations are traditional and are offered for reflection, not as guaranteed predictions.
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