What is zodiac sign compatibility?
Zodiac sign compatibility is the traditional astrological practice of comparing two people's Sun signs, the sign the Sun was in when each person was born. Astrology reads every sign through three attributes: an element (fire, earth, air or water), a modality (cardinal, fixed or mutable) and a polarity (positive or negative). It also reads the aspect, the angle between the two signs on the zodiac wheel.
This calculator uses the Western tropical zodiac and Sun signs only. It turns those traditional rules into one transparent compatibility index and shows every factor behind it. Astrology is an interpretive tradition, not a science, so the result describes how astrologers read a pairing. It can't tell you how a real relationship will go.
How to use the zodiac signs compatibility calculator
- For Person 1, choose Zodiac sign and pick a sign, or choose Birthday and enter the month and day.
- Do the same for Person 2.
- Read the compatibility index, its band, and the three factors: aspect, element and modality.
- Read the strengths and friction points, each labeled with the factor it comes from. Copy result copies the signs and the result as plain text.
The result updates as you choose, and it's the same whichever person you enter first. Everything is calculated in your browser.
How the compatibility index works
The index adds up points for the two attributes that describe every pairing of Sun signs:
| Factor | Relationship | Points |
|---|---|---|
| Element | Same element | 60 |
| Element | Complementary: fire with air, earth with water | 50 |
| Element | Contrasting: any other pair | 20 |
| Modality | Different modalities | 30 |
| Modality | Same modality | 15 |
compatibility index = element points + modality points
The index can range from 35 to 90. It's reported out of 100, but it stops at 90 on purpose: a comparison of two Sun signs leaves out most of what shapes a relationship. The same two signs always get the same index, in either order.
Why aspect and polarity aren't scored again
Around the wheel, the elements repeat every four signs, the modalities every three and the polarities every two. So once you know how many signs apart two signs are, you know all three relationships. Polarity matches exactly when the elements are the same or complementary, and each element-and-modality combination is exactly one aspect.
Scoring the aspect or polarity as well would count the same relationship two or three times. The calculator shows them, because they help explain the reading, but it doesn't add points for them.
The seven Sun-sign relationships
Every pair of signs falls into one of seven relationships:
| Relationship | Signs apart | Elements | Modalities | Index | Band | Example |
|---|---|---|---|---|---|---|
| Trine (120°) | 4 | same element | different modalities | 90/100 | Very harmonious | Aries + Leo |
| Sextile (60°) | 2 | complementary elements | different modalities | 80/100 | Harmonious | Aries + Gemini |
| Same sign (0°) | 0 | same element | same modality | 75/100 | Harmonious | Aries + Aries |
| Opposition (180°) | 6 | complementary elements | same modality | 65/100 | Mixed | Aries + Libra |
| Semi-sextile (30°) | 1 | contrasting elements | different modalities | 50/100 | Contrasting | Aries + Taurus |
| Quincunx (150°) | 5 | contrasting elements | different modalities | 50/100 | Contrasting | Aries + Virgo |
| Square (90°) | 3 | contrasting elements | same modality | 35/100 | Challenging | Aries + Cancer |
Ptolemy's Tetrabiblos, one of the founding texts of Western astrology, named four aspects. He called the trine and sextile harmonious and the square and opposition disharmonious. He grouped signs one or five apart as "disjunct," with no aspect at all, which is why the semi-sextile and quincunx share an index here. Modern astrologers often add more nuance: an opposition, for example, is usually read as complementary tension rather than simple conflict.
How to read your score
- Very harmonious (85–90): same element, different pace. Traditionally the easiest Sun-sign pairing.
- Harmonious (75–84): a sextile's friendly cooperation, or a same-sign pair's familiarity, which comes with doubled blind spots.
- Mixed (60–74): an opposition, where attraction and friction both come from the signs' differences.
- Contrasting (45–59): neighboring or quincunx signs, with no shared attribute. The connection rests on curiosity about difference.
- Challenging (below 45): a square, where both signs push the same way toward different goals.
A lower index isn't a verdict. In astrological terms, it means the pairing's strengths are less obvious from the Sun signs alone.
Zodiac compatibility chart
The index for all 144 combinations, from the same rules as the calculator. Read across from one sign and down from the other. The chart is symmetric, so each of the 78 unique pairings appears twice.
| Sign | Aries | Taurus | Gemini | Cancer | Leo | Virgo | Libra | Scorpio | Sagittarius | Capricorn | Aquarius | Pisces |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Aries | 75 | 50 | 80 | 35 | 90 | 50 | 65 | 50 | 90 | 35 | 80 | 50 |
| Taurus | 50 | 75 | 50 | 80 | 35 | 90 | 50 | 65 | 50 | 90 | 35 | 80 |
| Gemini | 80 | 50 | 75 | 50 | 80 | 35 | 90 | 50 | 65 | 50 | 90 | 35 |
| Cancer | 35 | 80 | 50 | 75 | 50 | 80 | 35 | 90 | 50 | 65 | 50 | 90 |
| Leo | 90 | 35 | 80 | 50 | 75 | 50 | 80 | 35 | 90 | 50 | 65 | 50 |
| Virgo | 50 | 90 | 35 | 80 | 50 | 75 | 50 | 80 | 35 | 90 | 50 | 65 |
| Libra | 65 | 50 | 90 | 35 | 80 | 50 | 75 | 50 | 80 | 35 | 90 | 50 |
| Scorpio | 50 | 65 | 50 | 90 | 35 | 80 | 50 | 75 | 50 | 80 | 35 | 90 |
| Sagittarius | 90 | 50 | 65 | 50 | 90 | 35 | 80 | 50 | 75 | 50 | 80 | 35 |
| Capricorn | 35 | 90 | 50 | 65 | 50 | 90 | 35 | 80 | 50 | 75 | 50 | 80 |
| Aquarius | 80 | 35 | 90 | 50 | 65 | 50 | 90 | 35 | 80 | 50 | 75 | 50 |
| Pisces | 50 | 80 | 35 | 90 | 50 | 65 | 50 | 90 | 35 | 80 | 50 | 75 |
Highest and lowest index for each sign
| Sign | Dates | Element, modality | Highest (90) | Next (80) | Lowest (35) |
|---|---|---|---|---|---|
| Aries | Mar 21 – Apr 19 | Fire, cardinal | Leo, Sagittarius | Gemini, Aquarius | Cancer, Capricorn |
| Taurus | Apr 20 – May 20 | Earth, fixed | Virgo, Capricorn | Cancer, Pisces | Leo, Aquarius |
| Gemini | May 21 – Jun 20 | Air, mutable | Libra, Aquarius | Aries, Leo | Virgo, Pisces |
| Cancer | Jun 21 – Jul 22 | Water, cardinal | Scorpio, Pisces | Taurus, Virgo | Aries, Libra |
| Leo | Jul 23 – Aug 22 | Fire, fixed | Aries, Sagittarius | Gemini, Libra | Taurus, Scorpio |
| Virgo | Aug 23 – Sep 22 | Earth, mutable | Taurus, Capricorn | Cancer, Scorpio | Gemini, Sagittarius |
| Libra | Sep 23 – Oct 22 | Air, cardinal | Gemini, Aquarius | Leo, Sagittarius | Cancer, Capricorn |
| Scorpio | Oct 23 – Nov 21 | Water, fixed | Cancer, Pisces | Virgo, Capricorn | Leo, Aquarius |
| Sagittarius | Nov 22 – Dec 21 | Fire, mutable | Aries, Leo | Libra, Aquarius | Virgo, Pisces |
| Capricorn | Dec 22 – Jan 19 | Earth, cardinal | Taurus, Virgo | Scorpio, Pisces | Aries, Libra |
| Aquarius | Jan 20 – Feb 18 | Air, fixed | Gemini, Libra | Aries, Sagittarius | Taurus, Scorpio |
| Pisces | Feb 19 – Mar 20 | Water, mutable | Cancer, Scorpio | Taurus, Capricorn | Gemini, Sagittarius |
Worked examples
Aries + Leo: trine
Both are fire signs, so they share an element (60 points), and they differ in modality, cardinal + fixed (30 points): 60 + 30 = 90/100, very harmonious. Traditional astrology describes this as an energetic pairing with shared instincts and different paces.
Taurus + Cancer: sextile
Earth + Water is a complementary element pair (50 points), and fixed + cardinal are different modalities (30 points): 50 + 30 = 80/100. The reading is supportive and cooperative, though both signs may avoid raising problems directly.
Gemini + Gemini: same sign
Everything is shared. The element earns 60 points, but the modality earns only 15, because both signs are mutable: 60 + 15 = 75/100. That's lower than the trine and sextile: astrology reads two people of the same sign as doubling both their gifts and their blind spots.
Leo + Aquarius: opposition
Fire + Air is complementary (50 points), but both signs are fixed (15 points): 50 + 15 = 65/100, mixed. Opposite signs are traditionally described as each showing the other a missing half, with balance as the ongoing task.
Virgo + Sagittarius: square
Earth + Fire is a contrasting pair (20 points), and both signs are mutable (15 points): 20 + 15 = 35/100, the lowest index. Astrologers read the square as friction between two adaptable signs heading in different directions, which can also push both to grow. For comparison, the neighboring signs Libra + Scorpio share nothing at all and score 50/100.
Birthdays and zodiac cusp dates
In birthday mode, the calculator looks up each Sun sign from the common date ranges shown in the table above, using the month and day only. Those ranges are a convention. The Sun's entry into each sign shifts by about a day from year to year, and its calendar date depends on the time zone: the March equinox, when the Sun enters Aries, falls on March 19, 20 or 21. In 2026 the Sun entered Aries at 14:46 UTC on March 20 (10:46 a.m. in New York), so anyone born after that moment was an Aries by the Sun's position, even though the common ranges call March 20 Pisces.
Because of this, the calculator flags any birthday within two days of a sign change and names the neighboring sign it might belong to, with a button to compare that sign instead. It doesn't pretend to calculate the exact Sun position. That needs the birth year, time and place, and an astronomical ephemeris. If you know your sign from a birth chart, choose it directly. In astrology the Sun is in exactly one sign at any moment, so a cusp birthday belongs to one sign or the other.
Sun-sign compatibility vs synastry
Sun-sign compatibility compares one factor per person. Synastry, the fuller astrological method, compares two complete birth charts: the Moon, rising sign (Ascendant), Venus, Mars and other planets, and the exact angles between them. It needs each person's birth date, time and place. Two people with a low Sun-sign index can have a very different picture in synastry, and this calculator doesn't attempt it.
Is zodiac compatibility scientific?
No. Astrology hasn't been shown to predict personality or relationship success. A 2007 University of Manchester analysis of census records for about 20 million married people in England and Wales found that couples' Sun-sign combinations occurred about as often as chance would predict. In a double-blind test published in Nature in 1985, astrologers did no better than chance when matching birth charts to personality profiles.
That's why the index is called interpretive. It follows this page's published astrology rules, and it isn't a probability, a measurement or a forecast. Real relationships depend on communication, values, circumstances and choices that no zodiac sign can capture. Many people still enjoy astrology as a shared language for talking about personality and differences, and that's the spirit this calculator is built for.
Methodology and sources
The calculator stores the 12 signs with their traditional element, modality and polarity, measures the whole-sign distance between two signs, and applies the point table above. It doesn't use pair-by-pair scores. Every number on this page, including the chart, comes from the same engine as the calculator. Our methodology explains how calculators are built and tested, and the calculator disclaimer explains their limits.
- Aspects and disjunct signs: Ptolemy, Tetrabiblos, Book I, chapters 13 and 16 (Robbins translation, LacusCurtius)
- Marriages and Sun signs: "Love not in the stars", Phys.org report of David Voas's University of Manchester study (2007)
- Astrology and personality: Carlson, "A double-blind test of astrology", Nature 318, 419–425 (1985)
- Equinox and solstice dates: U.S. Naval Observatory, Earth's Seasons