What this calculator does
The Zodiac Sign Compatibility Calculator turns two birthdates into their Western (tropical) sun signs and returns a compatibility score from 0 to 100. It is built for fun, curiosity and conversation — it is an astrology-based estimate, not relationship advice. The model is universal (no country rules apply) and uses the common Western sun-sign date ranges.
How to use it
Pick the birth month and day for each person and press calculate. The tool identifies each sun sign, finds the element of each sign, and reads a score from a fixed element-compatibility matrix. You will see both signs, their elements, and the overall percentage match.
The formula explained
First each date is mapped to a sign using standard cutoffs — for example Aries runs March 21 to April 19, Cancer June 21 to July 22, and so on. Each of the 12 signs is assigned one of four classical elements: Fire (Aries, Leo, Sagittarius), Earth (Taurus, Virgo, Capricorn), Air (Gemini, Libra, Aquarius) and Water (Cancer, Scorpio, Pisces). A 4×4 matrix then assigns a base score: same element pairs score highest (95), Fire–Air and Earth–Water are very harmonious (90), while opposing temperaments like Fire–Water (50) score lower. Identical signs receive a small +3 bonus.
$$\text{Score} = M\!\left[E(s_1),\, E(s_2)\right] + 3\cdot\mathbb{1}\{s_1 = s_2\}$$
$$\left\{ \begin{aligned} s_1 &= \text{Sign}\!\left(\text{Month 1},\ \text{Day 1}\right) \\ s_2 &= \text{Sign}\!\left(\text{Month 2},\ \text{Day 2}\right) \\ E &= \text{Element of sign (Fire, Earth, Air, Water)} \\ M &= \text{Element compatibility matrix (50–95)} \end{aligned} \right.$$
Worked example
Person 1 born March 21 is an Aries (Fire). Person 2 born July 23 is a Leo (Fire). Both share the Fire element, so the matrix returns 95. The signs differ, so no bonus is added — the final compatibility score is 95%.
$$\text{Score} = M[\text{Fire},\, \text{Fire}] + 3\cdot\mathbb{1}\{\text{Aries} = \text{Leo}\} = 95 + 0 = 95\%$$
FAQ
Which date system is used? The standard Western tropical sun-sign ranges, the same ones used by most newspaper horoscopes.
What if both people share the same sign? They get the full same-element score (95) plus a 3-point bonus, for 98.
Is this scientifically accurate? No. Astrology is not a science. Treat the result as light-hearted entertainment.
