How Popular Would I Be
in an Isekai World? 🌙

Saju (사주) is Korea's traditional Four Pillars birth-chart system — the fortune-reading you'll see referenced across K-dramas, webtoons, and half the couples' first dates in Seoul. It transcribes the year, month, day, and hour of your birth into four "pillars" of two characters each. The upper character is one of ten heavenly stems (Gap, Eul, Byeong, Jeong, Mu, Gi, Gyeong, Sin, Im, Gye) and the lower one is one of twelve earthly branches — the twelve zodiac animals. Eight characters in total, which is why Koreans call it saju palja: "four pillars, eight characters". Pairing stems and branches in order yields a cycle of sixty combinations — the sexagenary cycle that East Asia has used to label days and years for centuries.

The pillar for your birth day is the day pillar, and its upper character is the day master — the standard English term among Four Pillars practitioners. Saju theory treats that single character as "you" and reads the other seven as the stage around you. That is why this test can assign a position from your birth date alone: the position comes from the day master, and the day master is fixed the moment your date is. The one-line "your day pillar" comment on the result screen is likewise one of sixty prepared lines, one per combination.

Up to the point of extracting the eight characters, no interpretation is involved — old East Asian calendars printed each day's stem-branch pair right on the page, and a chart just transcribes your birth moment into that notation. Interpretation starts afterward, and that is where schools diverge. The isekai position assignments below are this page's own house rules, not saju orthodoxy. To see your eight characters properly, use the Korean calendrical calculator (in Korean).

The ten heavenly stems are the five elements — Wood, Fire, Earth, Metal, Water — each split into yang and yin. Yang Wood (Gap) and yin Wood (Eul) are both wood, but behave nothing alike. Since popularity is ultimately a question of how you reach other people, this test mapped each stem's way of moving outward onto one position. (And yes — "isekai", the Japanese term for another-world stories, is used as-is: the genre is global now.)

Gap 甲 and Eul 乙 — the Wood day masters

Gap, yang Wood, is the great tree growing straight toward the sky, timber fit for a building's pillars. It starts things, it leads, and it does not bend once a direction is set. This is popularity by pure frontal assault, no tricks — so Gap becomes Everyone's Hero. The classic protagonist slot.

Eul, yin Wood, is the flower and the vine: it never pushes head-on, it winds around the wall and climbs, and it stands back up after being trampled. A character that wraps softly around people's hearts — the Guild Receptionist. Gathering a crowd without ever swinging a sword is the Eul way.

Byeong 丙 and Jeong 丁 — the Fire day masters

Byeong, yang Fire, is the midday sun: impossible to hide, reaching far and evenly, holding no grudges. The widest-radiating presence among the ten stems, so it sings in the middle of the plaza as the Kingdom's Bard. It is also why Fire gets the highest base score in the formula below.

Jeong, yin Fire, is the lamp and the hearth. It doesn't blanket the world like the sun, but it earns its keep when it's dark and warms one spot for a long time. The center of warmth people gather to at night: the Legendary Innkeeper. Deep regulars instead of broad fame.

Mu 戊 and Gi 己 — the Earth day masters

Mu, yang Earth, is the mountain and the levee: broad, thick, unmoved — and unwilling to move. The fewer words, the more weight. That is the Legendary Blacksmith: the kind of popularity that makes people come to you.

Gi, yin Earth, is the soil of fields and paddies. Instead of blocking like a mountain, it grows and nurtures. A born life-saver, transplanted directly as the Nation's Healer — never flashy, but the name everyone calls at the end.

Gyeong 庚 and Sin 辛 — the Metal day masters

Gyeong, yang Metal, is unpolished ore, pig iron, the axe: harder with every blow, fast to decide, zero excess. Popularity proven by results instead of words — the Silent Sword Saint.

Sin, yin Metal, is the finished jewel, the needle, the honed blade: precise, fastidious, allergic to mess. Refined beauty as a weapon in itself — the Court Mage.

Im 壬 and Gye 癸 — the Water day masters

Im, yang Water, is the ocean and the great river: enormous in scale, intolerant of confinement, naturally gathering people and stories. The whole continent is the stage — the Adventurers' Guild Master.

Gye, yin Water, is rain, dew, and morning mist: it seeps in silently and never quite takes a shape. The less substance people can pin down, the bigger the stories get — the Mysterious Spirit, the only position whose fame grows the less it appears.

The eleventh and twelfth — the Demon Lord and the Mastermind

There are twelve positions rather than ten because two conditions sit on top of the day masters. The first is Goegang (괴강, 魁罡): six specific day pillars out of sixty — Mujin, Gyeongjin, Imjin, Musul, Gyeongsul, Imsul — which saju calls the "chieftain star", an extreme, forceful charisma. Born on one of these six pillars, you become the Demon Lord regardless of day master, with +14 to your popularity score. Exactly 2,228 of the 22,280 dates between 1950 and 2010 — precisely 10.00% — land here.

The second is the Legendary Mastermind. This one is decided by score, not pillar: a non-Goegang chart with popularity 97 or above flips to Mastermind. Only 141 days in the same period — about 0.63%. The Goegang check runs first, so even a 99 popularity born on a Mujin day is a Demon Lord, not a Mastermind.

How the best party member and the fated rival were chosen

The best party member pairings are five mutual couples: Gap–Gi, Eul–Im, Byeong–Jeong, Mu–Gyeong, and Sin–Gye. Gap and Gi form what saju calls the Gap-Gi combination, a classic stem pairing; the other four are relations where one side produces the other (Water feeds Wood, Earth feeds Metal, Metal feeds Water) or the two share an element. Teammates who push each other up, in other words.

The fated rival is looser. Only three pairs point at each other — Gap–Gyeong (Metal chops Wood), Eul–Jeong, Byeong–Sin — and the rest are one-directional grudges. Rather than mapping mechanically from element clashes, the rivals were chosen where the kind of popularity overlaps — the Blacksmith and the Court Mage, say, feuding over the artisan-fame demographic. The Demon Lord and the Mastermind get bespoke lines instead of pairings.

The popularity score is built in the following order. The rules are invented for the isekai setting, but the same rules apply to everyone.

1. Base score — The starting point depends on the day master's element: Wood 52, Fire 58, Earth 48, Metal 45, Water 55. Fire, which radiates presence the widest, starts highest; Metal, which hardens inward, starts lowest.

2. Relations with the rest of the chart — The elements of your year, month, and day branches (plus the hour branch if entered) are scored by their relation to your day master. The output star — the element your day master produces — is worth +8, the biggest bonus. In saju the output star stands for speech, expression, talent, and showing yourself, so a popularity test makes it king. The wealth star (the element you control) is +3, the officer star (the element that controls you) −2, peers (your own element) −3, and the resource star — the element that produces you — is −6, the biggest penalty: learning, protection, and gathering inward point away from outward popularity. This is the exact inverse of the zombie test, where the resource star was the top bonus.

3. Positional weights — The month branch counts ×1.5, the year branch ×1.3, the day branch ×1.2, the hour branch ×0.7. Weighting the month heaviest follows the saju convention of treating the season of birth as the chart's root.

4. Yin and yang — Yin day masters (Eul, Jeong, Gi, Sin, Gye) get +2; yang ones (Gap, Byeong, Mu, Gyeong, Im) get −2. In a world where delicacy is charm, the yin stems get the edge — also the reverse of the zombie test.

5. Goegang — The six chieftain-star pillars get +14.

6. Scatter — Without it, everyone sharing a day pillar would score nearly the same. So the birth-date string goes through a fixed hash function, adding two deterministic offsets of up to ±25 and ±7. Not random: the same date always gets the same offsets.

Finally, anything above 93 or below 7 is compressed by half and the result is clamped to 1–99. Over every date from 1950 to 2010 the formula averages 53.0 with a median of 53, and both extremes — 1% and 99% — actually occur. One more detail: a popularity below 30% automatically prepends a "small but fanatical following" paragraph to your reading; 12.7% of all dates qualify.

The "top N%" badge is not a comparison with other people who took this test — your input never leaves the browser, so there is no such data to compare. Instead the page ships a 99-slot percentile table: for every one of the 22,280 dates from January 1, 1950 through December 31, 2010, popularity was computed with birth time unknown, and for each value 1–99 we stored what fraction of dates (in per-mille) scores at or above it. Your result screen just looks your number up.

So read the badge as "top N% of all possible birth dates", not of test-takers. Reference points: popularity 54 is where you enter the top half (top 49%), 60 is top 38%, 70 is top 22%, 80 is top 10%, 90 is top 4%, and 97+ is the top 1%. Past the halfway mark on the other side, the badge picks up a "cult favorite" tag.

The isekai fan-club member count derives from popularity. The base value is (popularity ÷ 99) raised to the power 1.6, times 900,000, plus 3,000; a hash of your birth date then applies a 0.86–1.13× multiplier and some sub-1,000 loose change. The 1.6 exponent makes membership grow steeper as popularity climbs: around 20,000-odd members at 10%, 260,000–340,000 at 50%, 670,000–880,000 at 90%, clamped between 3,000 and 980,000. Same popularity, different birthday, different count — that's the multiplier at work.

None of the five values on screen — position, popularity, percentile, fan-club count, day-pillar line — involves a random function. Everything is computed from your birth date (and the time, if you chose one).

The day pillar is pure date arithmetic: convert the birth date to a running day number, take the remainder mod 60, done — the sexagenary cycle rolls over every sixty days without exception. The fiddly parts are the year and month pillars. In saju the year changes not on January 1 or Lunar New Year but at Ipchun, the "start of spring" term, and the month rolls at each of twelve solar terms. A solar term is the moment the sun reaches a specific angle, so its date and time differ every year. This page therefore embeds a minute-precision table of term times from 1900 on, and for an early-February birthday it compares against the clock to decide whether your year pillar is still last year's. Two people born on February 4 really can get different year pillars.

The eight (or six, without a time) characters then run through the formula above, and the final scatter offsets and fan-club multiplier also come from hashing the birth-date string. A hash gives the same output for the same input, always — so on any day, on any device, the same birthday produces the same screen. Comparing with friends only means something because of this.

My birthday is on the lunar calendar. Can I enter it as-is?

No. The input expects the Gregorian (solar) calendar. A lunar date entered directly can be off by nearly a month, which changes the day pillar wholesale — and with it your position. If you only know your lunar birthday, convert it to a solar date first (K-magpie's lunar–solar converter is in Korean).

Does not knowing my birth time change the result?

Your position does not change — it comes from the day pillar, which the date alone determines. What changes is the popularity number, and with it the percentile and fan-club count. A birth time adds one branch at ×0.7 weight and changes the hash input for the scatter; in practice popularity moves about 17 points on average with versus without a time. Without a time, noon is used as the representative value. On the handful of dates hovering near 97, the birth time can decide whether you become the Mastermind.

Another saju calculator gives me a different chart

This test uses one fixed convention, no options. Birth time is taken only as one of twelve two-hour slots (each slot's midpoint is used); there is no 30-minute standard-time correction and no "late Rat hour" rule, both of which vary by school. Practically, two groups may differ from a full calculator: births around 11 p.m., and births on a solar-term changeover day. For those boundary cases the calendrical calculator (in Korean) lets you toggle each convention.

My popularity came out painfully low

The biggest penalty in the formula is the resource star — the element that produces your day master — at −6 per branch. Several of them will visibly pull the score down. But in real saju the resource star is a fine character: it means learning, documents, and elders' care. This page simply defined popularity as "how far outward you go" and docked the inward-gathering energy — a house rule, not an astrological verdict. The very same chart scores high on the zombie test, in fact. For what those characters mean in a real reading, see Yaong Myeongni (in Korean).

Does the shared link contain my birth date?

No. The link carries only four result values — position number, popularity, fan-club count, day-pillar number — packed into one integer. Your birth date and time are not in it and cannot be reconstructed from it. The percentile isn't stored at all, since it follows from popularity via the table. Whoever opens your link sees only your result screen.

Why only 12 positions?

Because there are 10 day masters, plus the Goegang pillars and the Mastermind threshold. Within those 12, though, popularity (1–99), percentile, fan-club count, and one of 60 day-pillar one-liners combine — so the same position still yields a different screen for every person.

If you've read this far, you've guessed: this test is for entertainment only. The calendrical engine is a genuine computation over real solar-term data, but the rules that turn eight characters into isekai positions and percentages of popularity are entirely this page's invention. Korean saju contains, unsurprisingly, no concept of "isekai popularity" or "fan-club member counts".

Nor does the number predict anything about your real relationships. No sulking over a low score, no swaggering over a high one. The intended use is putting two phones side by side and settling who gets to be the Demon Lord. If saju itself caught your interest, check your eight characters at the calendrical calculator (in Korean) and read what they mean at Yaong Myeongni (in Korean).