Synastry
Compare two birth charts
Synastry compares two whole birth charts by measuring the angle from each of one person's planets to each of the other's. It is the technique underneath every compatibility quiz on the internet, and unlike a quiz it needs both birth charts rather than two star signs.
How this is calculated
The contacts
Every one of the first person's ten planets is measured against every one of the second's, which is a hundred comparisons rather than the forty-five a single chart makes. The difference matters: in one chart, Sun to Moon and Moon to Sun are the same angle measured twice, but across two charts they are two different contacts and the tradition reads them differently.
Contacts are ordered by how much they have to do with relating rather than by how tight they are. The Sun, Moon, Venus and Mars carry the most weight, Mercury, Jupiter and Saturn the next, and two slow planets together carry none at all. There are 40 written pairings behind the readings.
Why some contacts have no reading
A contact needs at least one personal planet, meaning the Sun, Moon, Mercury, Venus or Mars. Where neither is personal, everybody born within a few years shares the same contact: Uranus, Neptune and Pluto spend seven to thirty years in a sign, and even Jupiter and Saturn run on a twenty year cycle, so two people born two years apart have the same Jupiter-Saturn angle as several million other people.
Those contacts are detected and counted, and deliberately not interpreted. It is the same rule this site applies to a Neptune-Pluto aspect inside a single chart, where the honest reading is to say that it cannot tell you anything about an individual.
The score
Two thirds of it is how many strong contacts the two charts make and how tight they are. One third is how many of those are flowing rather than frictional. The conjunction counts towards neither, because whether two planets fusing is comfortable depends entirely on which two.
It is a description of two charts, not a prediction about two people, and it is shown with the counts it was built from so you can see that for yourself. A low number means the charts barely touch, which the tradition reads as indifference. Friction is not the poor outcome; the absence of anything is.
Sun sign compatibility, all 78 pairings
A far thinner reading than the tool above, and the one most people arrive looking for. Each cell is the angle between the two signs, which is what the tradition builds sign compatibility from. Aries with Leo is the same arrangement as Leo with Aries, so each pair has one page rather than two.
Two signs, straight to the pairing
Yours, usually.
Theirs. The order makes no difference to the result.
Choose both and the angle between them appears here.
- 0° The same sign
- 30° Next door
- 60° Two signs apart
- 90° Three signs apart
- 120° Four signs apart
- 150° Five signs apart
- 180° Opposite signs
Start with one chart
A comparison is much easier to read once you know your own chart. All of these are free and use the same ephemeris.
Questions about compatibility
Asked often enough to answer here.
Comparing two birth charts by measuring the angle between one person's planets and the other's. A contact between two charts is read as a specific dynamic between the two people, and the direction matters: one person's Saturn on the other's Moon is not the same as the reverse.
A third chart made by taking the midpoint of each pair of planets, read as the chart of the relationship itself rather than of either person. This site uses the midpoint composite, which is not the same as a Davison chart.
Not to get a result, but it matters. The Moon moves about half a degree an hour and Moon contacts are among the most important in synastry, so without a birth time the Moon may be in the wrong sign entirely. Composite angles cannot be calculated without both times.
No. The score describes how many strong contacts the two charts make and how many of those are easy rather than frictional. A low score means few contacts, which the tradition reads as indifference rather than conflict, and it treats friction as work rather than as failure.