Astrology compatibility, written in the stars

How the compatibility score works

The 0 to 100 score is a weighted average of five comparisons between two real birth charts: Moon synastry counts for 25%, the Sun-sign blend and Venus synastry 20% each, Mars synastry 15%, and the cross aspects among both charts' personal planets the remaining 20%. Each synastry component measures the actual angle between the two planets and scores it against the five classical aspects, from the trine at 120° (the strongest lift) to the square at 90° (the strongest drag), each with its own orb of tolerance.

None of it is looked up in a table of sun-sign verdicts. When you enter two sets of birth details, we geocode each birthplace, convert the local birth time to universal time, and compute both charts with astronomy-engine, an open-source ephemeris library accurate to well under a degree. If a birth time is missing we assume noon, which leaves the Sun, Mercury, Venus, and Mars accurate to roughly a degree. The methodology page documents every weight and orb in the pipeline.

What the free birth chart includes

The birth chart generator places all ten planets in the tropical zodiac, computes your Ascendant and Midheaven, and draws the twelve house cusps in your choice of four house systems: Placidus (the default), Whole Sign, Koch, or Equal. Every placement comes with a plain-language interpretation, so you get “Moon in Scorpio in the fourth house” and a paragraph on what that placement has traditionally meant, not just a glyph on a wheel. Charts print cleanly and can be regenerated anytime.

Common questions

Is Zodiac Match really free?

Yes. Compatibility scores, birth charts, daily transits, and the gemstone guides are all free to use, with no payment step anywhere on the site.

Do I need my exact birth time?

For a compatibility score, no. Scoring uses planetary longitudes only, so a missing time costs you at most 6.5° of Moon precision. For a full birth chart, yes: the Ascendant and house cusps shift about one degree every four minutes, so an exact time matters there.

Which zodiac do you use?

The tropical zodiac, the standard frame of Western astrology, where the signs are anchored to the equinoxes rather than to the constellations.

Where do the planetary positions come from?

From astronomy-engine, an open-source ephemeris library that returns true planetary positions for any moment, the same math astronomers use. Positions are accurate to well under a degree.

Can two signs be incompatible?

No pairing scores zero. Because the score blends five components, a hard Sun-sign combination can be offset by a close Moon or Venus contact. The score describes friction and flow, not a verdict.