What is Saju?
The short, honest version — no jargon.
The idea
Saju (사주, "four pillars") is a centuries-old Korean tradition that reads the energy of the year, month, day, and hour you were born. Each pillar mixes one of five elements (Wood, Fire, Earth, Metal, Water) with one of twelve animals — so you get a sign like "yin Wood Pig." It’s a cousin of Chinese Bazi, and it’s where K-drama characters get their fortunes told.
What Bokki actually does
We’ll be honest: Bokki is here for comfort and reflection, not certainty. We calculate your real Saju year-sign, then write you a warm reading around it. Think of it as a friendly nudge to know yourself and face today — not a prediction of the future.
Why people love it
A daily moment of calm, a little self-understanding, and one small thing to try today. That’s the whole point.
How the four pillars are actually built
From a calendar, not a template. The year turns at 立春 (around 4 February), so a birth in late January belongs to the previous year’s pillar. The month turns at the 24 solar terms (절기), not on the 1st. The day pillar is computed from the Julian Day Number against a fixed anchor — 1 January 2000 = 戊午 — and we checked it against an independent almanac for every day from 1900 to 2035: 49,673 days, not one mismatch. The hour pillar uses true solar time at your birthplace: your longitude against the timezone meridian, plus the equation of time. In Korea that shifts the clock by roughly half an hour, which is often enough to move you into a different hour branch.
What Saju does not settle
The boundary cases, said out loud. 子時 (23:00–01:00) splits the schools, and Bokki follows 야자시: a birth at 23:30 takes the next day’s stem for the hour pillar while the day pillar stays where it is. The 자정 school disagrees, and rather than pretend the question is settled we pin our version with a regression test. The starting age of a 대운 luck cycle is exact to within a year, because the remainder rule differs by school. And the layer above the arithmetic — strength, 용신, the reading itself — is judgment, not calculation. We keep those two apart on purpose, and we never put a number on another person’s choices.
Closing note — what building this actually taught us
To sum up: Saju is calendar arithmetic — four pillars set by 立春, the 24 solar terms, and true solar time — and everything above that arithmetic is interpretation. Bokki automates only the first half, on purpose.
This page follows the order in which we actually had to make decisions while building the calculator. The first thing that stopped us was not the prose — it was the boundaries. Seoul sits west of its timezone meridian (135°E), so the sun runs about 32 minutes behind the clock; build the hour pillar from clock time and a birth near a boundary lands in the wrong branch. So true solar time went in first. Then we had to pick a side on the midnight hour — we chose 야자시 and pinned the choice with a regression test instead of pretending the schools agree. And we only trusted the day pillar after checking every day from 1900 to 2035 against an independent almanac. Sections 4 and 5 above are those decisions written down — the part only someone who has actually done the calculation can write.