Saju feels intensely personal — eight characters drawn from the exact instant you arrived, unlike anyone else's. Run the numbers, though, and the picture gets a little more humbling.

A Saju chart is built from four pillars — year, month, day, hour — each one a pairing of a heavenly stem (one of 10) and an earthly branch (one of 12), together stepping through a 60-step cycle (60 being the lowest common multiple of 10 and 12). Year and day pillars can each land on any of those 60 combinations, more or less independently of each other over long stretches of time.

Month and hour pillars aren't free choices, though — they're locked to the pillar above them. Once you know the year's heavenly stem, the month's stem is fixed by a simple rule (ė˜Īí˜ļ둔ė›”ëē•, the "Five Tigers" rule), so a given year only ever produces 12 possible month pillars — one per calendar month. The same logic applies to the hour: once the day's stem is fixed, only 12 hour pillars are reachable for that day (ė˜Īėžë‘”ė‹œëē•, the "Five Rats" rule).

Multiply it out: 60 possible years × 12 month pillars per year × 60 possible days × 12 hour pillars per day = 518,400 possible eight-character charts, total. That's every Saju chart that has ever existed or ever will — a large number, but a finite, countable one.

Now compare that to the roughly 8 billion people alive today. If births were spread perfectly evenly across all 518,400 possibilities (they aren't — birth rates shift by year, season, and hour, and this site doesn't track that), the math works out to roughly 15,000 people currently walking around with your exact chart. Not 15,000 people who resemble you — 15,000 people with the identical eight characters, the identical Day Master, the identical 대ėšī pattern.

That's not a knock on Saju. Astrology of every kind works at the level of pattern, not fingerprint — even Western natal charts, built from continuous planetary positions rather than a 60-step cycle, describe broad tendencies shared by huge numbers of people born under similar skies. What Saju is actually good at is giving you a structured, internally consistent language for thinking about balance, timing, and temperament — not a claim that no one else shares your specific pattern. If anything, the shared-chart math points at something worth remembering: two people can have identical charts and live completely different lives. The chart describes a shape — what you build inside it is still entirely up to you.