Birth chart compatibility: compare two natal charts free

How this birth chart compatibility calculator works

The calculator casts both natal charts in your browser with the same ephemeris as the free birth chart on this site: the sun, moon and planets for the birth moment, plus the rising sign when a time and place are given. Then it lays one chart over the other and finds every aspect between them, the angles astrologers have read for centuries: conjunction, sextile, square, trine and opposition.

Each aspect is weighted by two things. How personal the planets are: the sun and moon count most, then Venus, Mars and the rising sign, then Mercury, with Jupiter and Saturn lighter still and the outer planets barely at all. And how exact the angle is: a trine one degree from perfect counts far more than one six degrees off. Contacts between two slow outer planets are dropped, because everyone born within the same few years shares them.

The weighted contacts add up to four scores out of 100: love (Venus, moon and sun first), communication (Mercury first), passion (Mars, Venus and Pluto) and stability (Saturn and the moon). The overall score is 35 percent love, 25 percent stability and 20 percent each for communication and passion. The scale is set so a typical pair lands near 60, and most pairs fall between about 35 and 85. Same two births, same result, every time.

What natal chart compatibility looks at: five placements

A full chart has more than ten points, but five carry most of the weight in a relationship, and the calculator shows them side by side with the relation between the two signs. The sun sign is the one most people know; the other four are where two charts usually surprise each other.

Reading a synastry chart: which aspects matter

In a synastry chart, the angle between one person's planet and the other's tells the story. Trines and sextiles are easy flows. Squares and oppositions are friction, which in love often reads as attraction as well as conflict. A conjunction blends the two planets, and is easy unless Saturn, Neptune or Pluto is involved, which adds weight, fog or intensity.

Some contacts are famous for a reason. One person's sun on the other's moon is the classic marriage contact: one shines, the other feels at home in it. Venus with Mars is attraction. Moon with moon in a trine is two people who calm each other down. Saturn on a partner's sun or moon is commitment, felt as either loyalty or restriction depending on the rest of the chart.

Astrology compatibility beyond the sun sign test

The sun sign test on the compatibility hub compares one point per person and scores the relation between the two signs. Birth chart compatibility compares all of them, so the two can disagree, and when they do the chart is the better guide. A Leo and a Taurus score low as sun signs because two fixed signs square each other. If the Leo's moon is in Taurus, though, the bull's sun lights up exactly what the lion needs to feel safe, and if the two sit within a few degrees the chart shows a sun and moon conjunction, the classic sign of a lasting bond.

The reverse happens too. Two sun signs of the same element can have moons that square and Venus signs that oppose, which is why some couples who look perfect on paper find daily life hard. Neither result is a prediction. A chart comparison shows where things come easily and where they will take work, and the people decide the rest.

Birthday compatibility: what dates alone can tell you

If you only know two birthdays, you still get most of the picture. The sun, Mercury, Venus and Mars move slowly enough that a date fixes their signs except on the rare day one of them changes sign. The moon is the exception: it crosses a whole sign in about two and a half days, so without a birth time the calculator casts it for noon and flags that it may fall in the next sign. The rising sign changes every two hours or so and needs both the time and the place.

So birthday compatibility, from dates alone, is reliable for sun, Venus and Mars, usually right for the moon, and silent on the rising sign. Adding even an approximate time helps the moon; adding the place as well unlocks the rising sign and the full set of contacts.

How to read your results

Start with the side by side list, not the score. If the moons share an element or sit in signs that get along, the relationship tends to feel safe whatever the suns say. Then look at the easiest and hardest contacts: they are the three strongest aspects of each kind, strongest first, written as your planet against theirs.

The four scores tell you where the weight falls. High love with low stability is a passionate pair that needs structure. High stability with low passion is a steady pair that needs play. A score in the 40s is not a warning; it means the easy contacts and the hard ones roughly cancel out, which describes a great many long marriages.

1. 1.Compare moons first. They decide how a bad week goes.
2. 2.Look for sun and moon contacts across the charts, the traditional sign of a lasting bond.
3. 3.Read Venus and Mars together for attraction, and Mercury for how you argue.
4. 4.Treat Saturn contacts as commitment, not as bad news.

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