How K-SaJu reads a love match: the five parts of a compatibility score

Compatibility is one of the first things people try in K-SaJu (Korean astrology). You enter two birthdays and get back a number. But a number with no explanation is just a number. Fun for a minute, then what? Here's exactly what goes into a love match score on Rocky Saju, what each part looks at, and how much weight it carries.

Five parts, weighted out of 100

Our score is built from five parts. Each one compares something specific in the two charts:

1. Needed-element support (30): does each chart carry what the other one is missing?
2. The love seat (25): how your two birthday animals get along
3. The two birthday natures (20): how the top characters of your birth days relate
4. Partner-sign condition (15): how the sign of a partner sits in each chart
5. Birth-year animals (10): the Korean zodiac pairing, kept for reference

Look at what sits at the bottom. The Korean zodiac match, the one most people have heard of, counts for the least, because it's the broadest layer of all and everyone born in the same year shares it, so it only gets a small say.

Needed-element support: the biggest part

Every chart leans. Always. One might be heavy on Fire and short on Water, another might be mostly Metal with very little Wood. K-SaJu works out the one element each chart needs most to get back toward balance. Our post on the five elements explains how that works.

This part asks a simple question: does the other person's chart carry your needed element? If it shows up once, that scores well, and twice or more scores a little better. A helper element that supports your needed one adds some too. If their chart leans hard, 40 percent or more, toward the one element that's toughest on yours, points come off. We check it in both directions and combine the two.

Why the top spot? Because it's about what two people bring each other over months and years, not just the first spark.

The love seat: your two birthday animals

Your birthday animal, the bottom character of your day pillar, is also called your love seat. It's where a partner sits in your chart, so it says a lot about daily life together: habits, home, and the small stuff.

Here's how the pairings score:

• A natural match (like Rat and Ox): +15
• On the same team (animals from the same group of three, like Monkey, Rat and Dragon): +8
• The same animal: +3
• Opposites that clash (like Rat and Horse): -8
• Rubbing each other the wrong way: -6
• A quiet tension: -8

A clash isn't a dealbreaker. Not even close. In our reading, two clashing animals are a pair that shakes each other up deeply, which can make the bond feel intense. It mostly means you'll need extra patience with each other's routines.

The two birthday natures

The top character of your day pillar stands for you, and the top character of theirs stands for them. How those two natures relate carries 20 points of weight:

• A rare natural pair, like Oak and Garden or Sun and Jewel, scores highest.
• If their nature matches your partner sign, that scores high too, with the steady form a bit above the intense form.
• If their nature feeds yours, the way water feeds a tree, it scores well.
• Sharing the same element adds a little.
• One person being the outward kind and the other the inward kind adds a small bonus.

We check this one from both sides and average it, too. It never matters who's typed in as "me".

Partner signs and the Korean zodiac

The partner-sign part looks at each chart on its own. Traditional K-SaJu gives each person an element that stands for a partner, and the rule differs by gender, which is one reason our forms ask for it. If your chart holds that sign, you get points. If that sign happens to be an element that's hard on your chart, a few come back off. And if the other person's birthday animal holds your partner sign, that counts in your favor as well.

Last comes the birth-year animal pairing, worth 10. A good pairing adds a little, an ordinary one adds nothing, and a clash or a quiet tension takes a little away. It's color. Not the main story.

The same score from either side

Our compatibility score is symmetric. Put yourself in as "me" and your partner as "them", then swap, and you'll get exactly the same number and the same result tier. We check this with automated tests every time the code changes. Only the wording shifts, so each of you reads the result from your own side.

Scores are shown on a scale from 60 to 97, and they fall into four tiers. On our Match page they read like this:

• 88 and up: "You two really pull each other in"
• 79 to 87: "A really good match"
• 71 to 78: "A match that grows on you"
• Below 71: "A match you build slowly"

In a test of 200 random pairs, the middle score was about 78. Only about 6 percent reached the top tier, and nearly half landed between 71 and 78. Land there and you're in very ordinary company.

A low score isn't a verdict

Think about everything the score can't see. It doesn't know how you talk to each other after a long day, whether you laugh at the same dumb jokes, or how you make up after a fight. It reads two birth moments and nothing more. A lower score points to places where your rhythms differ, and knowing that can actually help you understand each other.

A high score doesn't promise anything either. How a real person feels is beyond any chart, and that's true whether your number is 62 or 96.

Three ways to try it on Rocky Saju

• Match: for two people getting to know each other, or already together.
• Bias Match: pick a K-pop idol and see your chemistry, based on their publicly known birthday. It's purely for fun, it says nothing about any real person's feelings, and it's completely free.
• Reunion: for someone thinking about a past relationship. Please read it gently. It never tells you to get back in touch, and if the other person has asked for space, the kindest thing is to respect that. Every reunion result carries a reminder to honor their wishes.

For all three, the other person's birth date is used only to work out the result. We don't store it. You can choose to have your own details remembered in your browser, but never theirs.