How to read your results
Each line compares one planet in the first chart with one planet in the second and names the angle between them. Supportive angles (trines and sextiles) usually describe ease. Challenging angles (squares and oppositions) describe friction that can also create energy. Conjunctions blend two planets together. The tighter the orb, the stronger the effect.
The four areas (chemistry, communication, emotional fit and staying power) group the aspects that matter most for each theme. For the method behind it, read Synastry Explained, then go deeper on Venus and Mars, the Moon and Saturn.
How the calculation works
Birth time and city are converted to universal time using the city’s historical time zone. Positions of the Sun, Moon, Mercury, Venus, Mars, Jupiter and Saturn come from standard orbital elements; the rising sign comes from the birth time and the city’s coordinates. We checked the positions against an independent astronomy library over 3,000 random dates: the largest difference was about 0.1°, so signs and aspects are reliable. See the about page for more.
Frequently asked questions
What is a synastry calculator?
A synastry calculator compares two birth charts and lists the angles (aspects) between the planets in each. It shows where two people tend to feel ease, spark or friction with each other.
Do I need a birth time?
A birth time gives you the rising sign and a precise Moon. Without it you still get the planets and the aspects between them, but the Moon can be uncertain on days it changes sign, and the rising sign cannot be calculated.
How accurate is the calculation?
Planet positions are computed from standard orbital elements and checked against an independent astronomy library: across 3,000 random dates from 1935 to 2026, the largest difference was about 0.1° for the Moon and under 0.06° for the Sun and planets. That is far inside the 6° orb used for aspects. Positions near a sign boundary can differ by a hair.
Is my birth information stored?
No. The comparison runs in your browser and nothing you enter is sent to our servers. Only the city name you type is sent to Open-Meteo's public geocoding service to find coordinates and the time zone.
Does it include houses or outer planets?
Not yet. This calculator uses the Sun, Moon, Mercury, Venus, Mars, Jupiter and Saturn, and the rising sign. It does not use Uranus, Neptune, Pluto, the nodes, or house overlays.
Can it tell me if we will stay together?
No. Synastry describes tendencies and gives you language for patterns. It is a tradition of reflection, not scientifically validated as a predictor of relationship outcomes.
Orbit provides astrology for entertainment and self-reflection. Readings are not predictions and are not medical, psychological, legal or financial advice.