We Ran 36,525 Birthdays Through a Saju Engine. The Day Master Is Never Random — But Its Strength Is Rigged.

Editorial and entertainment purposes. This article reports what a calculation returns over a large set of dates; it does not predict anything about any person, and nothing here should inform a medical, legal or financial decision.

Most writing about Saju — including most of ours — explains the system. This one measures it.

We took every calendar day from 1 January 1925 to 31 December 2024, fixed the birth time at noon and the birthplace at Seoul, and pushed all of them through the SajuSis Four Pillars engine: 36,525 charts, true solar time applied, zero failures. Then we counted.

The script that produced every number below is in the repository as scripts/daymaster-study.mjs, so anything here can be regenerated rather than taken on trust.

The Day Master is perfectly, boringly even

First result, and it is the one that should be boring: each of the ten Heavenly Stems lands as the Day Master almost exactly one time in ten.

The spread between the most and least common Day Master across a century is one single day. By element it is the same story: wood, fire, earth, metal and water each take 20.00% of the day pillars.

This is not a finding about fate. It is the sexagenary cycle doing exactly what it is built to do — the day pillar advances one step per day through a 60-term loop, so over 36,525 days every stem gets its turn. It is worth stating anyway, because "rare Day Master" claims circulate constantly. There is no rare Day Master. If someone tells you yours is unusual, they are talking about the rest of the chart, not the stem.

The strength score is not even at all

Here is where it stops being boring.

SajuSis rates Day Master strength from 0 to 100 — how well supported that stem is by everything else in the chart. Across all 36,525 charts the mean is 50.32 and the median is exactly 50, which is what you would hope from a scale that is supposed to be centred.

But split that score by Day Master and the evenness collapses:

A 戊 Earth Day Master averages 71 out of 100. A 壬 Water Day Master averages 36. That is a 34.7-point gap between two stems that appear equally often, and it is not noise — each row is an average over roughly 3,650 charts.

The ordering is not random either. Earth and fire sit at the top; water and 甲 wood sit at the bottom. Earth is produced by fire and sits in the middle of the generating cycle with support arriving from several directions at once; water is produced by metal and drained by wood, and in a chart drawn from the Korean calendar it more often finds itself outnumbered.

The practical consequence: "my Day Master is weak" is a much less interesting statement than it sounds. If you are 壬 Water, a strength score of 36 is not a personal deficit — it is the median outcome for your stem. A 壬 chart scoring 55 is genuinely well-supported, while a 戊 chart scoring 55 is on the low side for Earth. Reading the raw number without knowing the baseline gets this backwards, and that is a mistake we have seen in a lot of published readings.

Across the whole population the three strength bands split almost in thirds: strong 34.24%, weak 33.96%, balanced 31.80%. So the labels themselves are well calibrated — it is only when you condition on the stem that the imbalance appears.

Which elements actually run high, and which go missing

The engine flags an element as excess or deficient relative to its expected share. Over 36,525 charts:

Runs to excess most often

Comes up deficient most often

Fire is roughly three times more likely to be in excess than to be deficient (27.84% vs 8.68%). Metal is the mirror image — deficient in a quarter of charts, excess in one in eight.

There is a mechanical reason. Charts built at noon carry a fire-heavy hour branch, and the hidden stems inside the earthly branches lean toward earth and fire more than they lean toward metal. This is a property of the noon/Seoul setup we chose, not a claim about humanity, and it is exactly the kind of caveat a study like this has to state out loud: change the fixed hour and these two tables move. The Day Master table above does not move, which is why we trust that one more.

Charts with a completely absent element are rarer than people assume

"I have no water in my chart" is a common line. How common is it really?

Roughly four charts in five contain all five elements. A missing element is a one-in-five event, not a default. And when something is missing, it is essentially always one of three:

• Water absent — 7.44% of charts
• Metal absent — 7.43%
• Wood absent — 7.42%

Fire and earth were never absent in any of the 36,525 charts. Not rare — zero. Again, partly the noon fixture, but it is a concrete result: if you were told your chart has no fire, either a different hour was used or something is wrong with the calculation.

And exactly one chart out of 36,525 came back missing three elements. One. That is what an actually unusual chart looks like — not a stem, but a structure.

What this does and does not establish

It establishes how a specific engine behaves over a specific century, with the hour and place held fixed. That is worth knowing because it gives every individual reading a baseline to be compared against — a score of 36 means one thing for water and another for earth, and until you measure the population you cannot say which.

It establishes nothing about anyone's life. The strength score is a description of internal chart support, not of capability, luck, health or outcome. No part of this study touches real people; every chart in it is a date on a calendar with a fixed noon timestamp.

We are publishing the numbers because the alternative — asserting that a Day Master is "rare" or that a strength score is "low" without ever checking against the distribution — is how a tradition turns into guesswork. Saju is deterministic arithmetic before it is anything else. The arithmetic can be counted, so we counted it.

Related reading

• The ten Day Masters — what each stem means, one page each
• The five elements — what each element describes and how they feed and check each other
• Day Master strength — the axis everything hangs on
• When one element dominates your chart

Method: computeSaju() from the SajuSis engine, one call per calendar day from 1925-01-01 to 2024-12-31, time: '12:00', place: 'Seoul', true solar time applied. 36,525 charts, 0 errors. Source: scripts/daymaster-study.mjs. This article does not predict or describe any individual's future, health or private life.