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MystarX
MystarX

Birth chart compatibility calculator

Enter both birth dates to see how your Sun, Moon, Venus and Mars work together. Free, no sign-up

You

Don't know the time? Leave it empty and we'll use noon

Partner

Don't know the time? Leave it empty and we'll use noon

Birth chart compatibility vs zodiac sign compatibility

Your zodiac sign is only the position of the Sun. A birth chart has ten planets, twelve houses and an ascendant. Birth chart compatibility, also called synastry, compares two whole charts: how one person's Moon responds to the other's Sun, whether Venus and Mars connect, and which of the partner's houses the planets fall into. That's why two couples with the same signs can get completely different results.

How the calculator works

We calculate where the planets were at the moment of birth using astronomical ephemerides, taking the city and time zone into account. Then we compare the key planet pairs: Sun with Sun, Moon with Moon and Sun, Venus with Mars. Each pair is scored by how the elements combine, and those scores add up to passion, emotions, romance, communication and long-term potential.

Why the time of birth matters

The Moon moves through a sign in about two and a half days, so without a birth time its sign is sometimes uncertain. The ascendant and houses change every few minutes, so a full reading with houses needs an exact time. Without one, the calculator uses noon, and the Sun, Venus and Mars results stay accurate.

Frequently Asked Questions

Planet positions are calculated with astronomical precision. The free score uses the four main planets. The full reading adds aspects, houses and Saturn - the factors that most often explain why a couple lasts for years or drifts apart.
Yes. Without a time we use noon: the Sun, Venus and Mars will be exact, and the Moon almost always. The ascendant and houses can't be calculated without a time.
No. Tense combinations show where a couple needs to find common ground, not a ban on the relationship. Many strong couples have tense aspects - they bring passion and growth.
A zodiac test compares only the Sun, about a tenth of the chart. Here the Moon, Venus and Mars count too, and the full reading looks at the whole chart, aspects and houses included.
Synastry is the astrological method of laying two birth charts over each other. The astrologer looks at which of the partners' planets form aspects and which houses they fall into.