What the Zodiac Compatibility Calculator does
This calculator compares two star signs the way traditional astrology does and shows exactly how it reaches its verdict: the distance between the signs around the zodiac, whether their elements suit each other, and whether their modalities clash, each worth a fixed number of points that add up to a percentage. Pick two signs, or enter two birth dates and the Sun signs are found from where the Sun actually was.
Compatibility scores on most sites are a single number with no working. Here every point is visible, the rules are the standard ones from astrology books, and the whole thing is labelled for what it is: astrological tradition, not science. No study has found that Sun signs predict how relationships go, so treat the result as a conversation piece, not advice.
How to use it
- Choose "Star signs" and pick both signs, or choose "Birth dates" and enter both dates.
- Read the headline score and band - very harmonious, harmonious, mixed or challenging in tradition.
- Check the rule table: distance around the zodiac (up to 30 points), element pairing (up to 30) and modality pairing (up to 20), with what each pairing traditionally means.
- If a birth date was a cusp day, a warning says when the Sun changed sign that day; the noon sign is used.
- Scroll to the chart of the first sign with all twelve signs to compare other pairings at a glance, and download it as CSV.
Reading the results
Signs four apart (a trine) share an element and are the most harmonious pairing in tradition; signs three apart (a square) share a modality but clash in element and score lowest.
Elements pair as Fire with Air and Earth with Water (complementary), Fire with Earth and Air with Water (neighbouring), and Fire with Water and Earth with Air (contrasting).
Two signs of the same modality - both cardinal, both fixed or both mutable - are read as competing for the same role, so they earn fewer points than a mixed pair.
The percentage is just points out of 80. A pair at 45% is not "less than half compatible"; it means two of the three traditional rules give it a low rating.
Worked example: Aries and Leo, then Aries and Cancer
Aries is the first sign and Leo the fifth, four signs apart: a trine, 30 points. Both are Fire signs, the same element: 30 points. Aries is cardinal and Leo fixed, different modalities: 20 points. Total 80 of 80, so 100%, very harmonious in tradition.
Aries and Cancer are three signs apart: a square, 5 points. Fire with Water is a contrasting pair: 8 points. Both are cardinal: 10 points. Total 23 of 80, which is 23 / 80 x 100 = 28.75, rounded to 29% - challenging in tradition.
Formulas and scoring rules
- Distance points
k = |sign A - sign B| folded to 0..6; points = [20, 10, 25, 5, 30, 8, 18][k]Same sign, semi-sextile, sextile, square, trine, quincunx, opposition.- Element points
same 30; complementary 25; neighbouring 12; contrasting 8- Modality points
different 20; same 10- Score
percent = round(total / 80 x 100)- Sun sign from a date
sign of the Sun's apparent longitude at 12:00 UTC; cusp if the Sun changed sign anywhere between UTC-12 and UTC+14 on that date
Limitations: what the result does not prove
- Only Sun signs are compared. Astrologers who do synastry also compare Moon, Venus, Mars and the ascendant, which need birth times; the birth chart calculator gives those positions.
- The point values are a transparent encoding of the usual textbook rules, not a measured or validated scale. Another astrologer could weight them differently.
- Cusp birthdays are resolved at noon UTC. If the Sun changed sign that day, the true sign depends on the birth time and place.
- This is astrological tradition, not science, and should not be used to make decisions about relationships.
Privacy: where your data goes
Everything you paste, type or drop is processed in this browser tab. It is not uploaded, logged, stored or sent to analytics. Session recording and tag-manager scripts are switched off on this page.
Standards and sources
Frequently asked questions
How is a zodiac compatibility percentage calculated?
Here, by three published rules: the angle between the two signs (up to 30 points), how their elements pair (up to 30) and whether their modalities match (up to 20). The points are added and divided by 80. Every step is shown in the rule table.
Which zodiac signs are most compatible?
In tradition, signs of the same element four signs apart, such as Aries with Leo or Sagittarius, Taurus with Virgo or Capricorn, Gemini with Libra or Aquarius, and Cancer with Scorpio or Pisces. Those trine pairs score 100% here.
Can I check compatibility by birth date?
Yes. Switch to birth dates and enter both. The tool finds each Sun sign from where the Sun really was that day, which is more accurate than a table of sign dates and flags birthdays on a cusp.
Are opposite signs compatible?
Tradition calls opposites complementary: they sit on the same axis with elements that suit each other, like Aries and Libra. They score in the middle here because opposition is read as attraction with tension.
Is zodiac compatibility scientifically proven?
No. There is no controlled evidence that Sun signs predict how well two people get on, and astrology is not accepted as a science. The page labels its result as astrological tradition so it is clear what the number is and is not.
What does a cusp birthday mean for compatibility?
The Sun changes sign at a particular minute, usually around the 20th to 23rd of the month. If it happened on your birthday, your Sun sign depends on the time and place of birth; the page tells you when the change happened and uses the noon sign.
Last reviewed by the A2Z.Tools team against the sources listed above.
