I remember when I was younger I would always use the “love calculators” online where you input your name and your person of interest’s name and it would tell you how compatible you are. It didn’t take long for me to realize these calculators were totally random. The dead give away was when I would use the same calculator again with the same names and it would give me a different compatibility every time. As I’ve gotten older my interest in love and compatibility hasn’t faded but I’ve switched from random love calculators online to astrology. Disclaimer, this is purely for fun and I’m not saying your astrological compatibility with someone is an end all be all however it can give you insight into where you may struggle or attract.
Jumping straight into it, the first thing you’re going to want to know is modality and element. Every sign is either cardinal, fixed, or mutable and every sign is either fire, earth, air, or water. There are 12 signs and each is a unique combination of element and modality. Aries is cardinal fire, taurus fixed earth, gemini mutable air, cancer cardinal water, leo fixed fire, virgo mutable earth, libra cardinal air, scorpio fixed water, sagittarius mutable fire, capricorn cardinal earth, aquarius fixed air, and pisces mutable water. Now that you know each sign’s modality and element, you have to apply it to compatibility. When it comes to elements each element is compatible with its own element so fire and fire are compatible, air and air, etc. Fire and air are also compatible, and earth and water. Fire and air are complementing elements, Water and earth are complementing elements. Fire and earth, fire and water, earth and air, and water and air are not compatible. Fire and earth are different elements, fire and water are opposing elements, earth and air are opposing elements, and water and air are different elements.
Now onto modality compatibility. Unlike with elements, modalities are not compatible with their own modality so mutable and mutable are not compatible, cardinal and cardinal are not compatible, etc. Elemental compatibility is stronger than modality compatibility. Using this combined knowledge of element and modality you can breakdown each zodiac combos compatibility. Looking at element, if you are a sagittarius (mutable fire) you are most compatible with aries (cardinal fire), leo (fixed fire), libra (cardinal air), and aquarius (fixed air). Looking at element and modality you are 50/50 compatible with other sagittarius (mutable fire), and gemini (mutable air). You are 66/33 compatible (66 being not compatible, 33 being compatible) with taurus (fixed earth), cancer (cardinal water), scorpio (fixed water), and capricorn (cardinal earth). As a sagittarius you are not compatible with virgo (mutable earth) and pisces (mutable water). This formula applies to all signs, you will be most compatible with the same element or complementing element and different modality. You will be 50/50 compatible with the same element or complimenting element and the same modality. You will be 66/33 compatible with different or opposing element and different modality. You will not be compatible with different or opposing element and same modality.
Now you could stop here and use this information for just your sun sign (the one determined by your birthday alone that everyone is most familiar with) or you can use this formula to determine your individual placements compatibility (mars aries and mars libra or moon scorpio and moon taurus). If you choose to use your individual placements to determine overall compatibility the most important placements would be Venus, Mars, Moon, Sun, and Mercury in that order. An example of this would be if I am a Sun sagittarius, Moon scorpio, Mercury leo, Venus aquarius, and Mars libra and my partner was a Sun capricorn, Moon taurus, Mercury cancer, Venus virgo, and Mars aries. Our sun compatibility would be 66/33, Moon compatibility 50/50, Mercury compatibility 66/33, Venus compatibility 66/33, and Mars compatibility 50/50. Putting this in order of placement importance we get 66/33, 50/50, 50/50, 66/33, 66/33. Overall this would be a difficult relationship, most likely miscommunication, different approaches to life, different ways of problem solving, and different ways of handling emotions. It is not impossible to make this work, it would just require a lot of effort and understanding. Astrology is not an exact science, and this is just how I have combined my knowledge of astrology and personal opinions to determine a method of calculating compatibility so by no means is this the only way to calculate astrological compatibility.