Study Luck (學業星): How Is It Actually Calculated?
One fixed lookup — the element that generates your day master — decides your baseline. One heavenly stem decides how a single exam day feels. Nothing else enters this calculation.
Bokki Editorial
The short answer
Bokki's /exam screen shows one of two baseline sentences, and the choice comes down to a single check: is your resource element (인성, 印星 — the element that generates your day master, sometimes called the "study star") also one of your chart's favorable elements? That's the entire question. No exam subject, no target score, no probability of passing is part of this calculation — it reads exactly one relationship out of the same favorable-element list every other Bokki screen uses. If you also give an exam date, a second and completely independent sentence appears: it reads only that day's heavenly stem — one of ten, cycling every ten days — against the same favorable/unfavorable list, and lands on one of three fixed shapes: supportive, pressing, or neutral. The two readings never touch each other. One is set for life by your chart; the other resets every ten days regardless of who you are.
The rule — a resource lookup, then a same-day stem check
Every day master belongs to one of five elements, and each element has exactly one "resource" element — the one that generates it in the standard productive cycle (相生). Bokki's engine gets this table by taking the same five-line "generates" table every element-cycle screen already uses and flipping it around: Metal's resource is Earth (Earth generates Metal), Water's is Metal, Wood's is Water, Fire's is Wood, and Earth's is Fire. If that resource element sits inside the list of elements your whole chart currently needs most (your favorable elements — a separate calculation that reads your chart's strength and the season you were born in), you get the encouraging line; if it doesn't, you get the line about short, repeated study sessions instead. Neither line is graded better than the other in the code — they're simply the two shapes a resource-favorable check can take. The exam-day reading is a completely different, much smaller calculation: it takes the single heavenly stem of the calendar day you name (one of ten, since there are only ten heavenly stems total, so this reading repeats on a fixed ten-day cycle no matter the day of the week) and checks it against the same favorable list one more time. If that day's stem matches your resource element or sits in your favorable list, the day "supports" you; if it matches your one unfavorable element instead, the day "presses"; anything else reads as a neutral, unremarkable day.
Worked example — one person, two readings, and a birth-time flip
Take the chart Bokki's daeun, sipsin and guardian articles already use: born 15 May 1990, 14:30, Seoul — day master Metal (庚). With the birth time included, this chart reads weak and its favorable elements are Water, Earth and Metal, in that order. Metal's resource element is Earth, and Earth is on that list — so this person gets the encouraging baseline sentence. Now drop the birth time and keep only the birth date: the whole chart's strength reading flips from weak to strong (the hour pillar was carrying real weight in that judgment), and the favorable list changes completely, to Water, Wood and Fire. Earth is no longer on it, so the same person, same birthday, now gets the other sentence — the one about short repeated sessions. Nothing about this person changed; only whether Bokki knew their birth time did. Across a full census of every day from 1940 to 2019 checked against every two-hour branch window (350,640 pairs), this exact flip happens 11.81% of the time — a little more than one birthday in nine. Now the exam-day half, using the same person's weak-chart reading: on 4 September 2026 the day stem is Metal, which sits in that chart's favorable list, so the day reads supportive. On 9 September 2026 the day stem is Fire — this chart's one unfavorable element — so the day reads as pressing. On 17 September 2026 the day stem is Wood, which is neither favorable nor unfavorable for this chart, so the day reads neutral. Measured across the same 1940-2019 census (29,220 days times the ten-stem cycle, 292,200 pairings), those three shapes land 58.0%, 11.7% and 30.3% of the time respectively — most exam days are quietly supportive, and only about one in nine is genuinely pressing.
What this calculation doesn't decide
This calculation names one structural relationship (your resource element vs. your favorable list) and one same-day comparison (a stem vs. the same list) — it says nothing about how hard an exam is, what subject it covers, how many hours you've studied, or your actual odds of passing, and Bokki's own copy for this screen says so directly ("luck only supports — studying is what passes"). It also doesn't read the exam day's earthly branch at all — only the heavenly stem — so the day's zodiac animal, which many almanac traditions also weigh, plays no role here; that is a deliberate, narrower reading than some classical exam-day methods use, not an oversight. And it never turns any of this into a number or percentage shown to you: the three-shape exam-day reading and the two-sentence baseline are the only outputs, by design (Bokki's own no-score policy) — the percentages in this article exist to explain the code, not to appear on your screen.
Closing note — one lookup, one stem, and a birth time that can flip everything
In short: your study-luck baseline is a single yes/no check on whether the element that generates your day master is also an element your chart currently favors, and your exam-day reading is that same check run against one day's heavenly stem instead of your whole chart. Both are simple by construction — and both are sensitive to information you might not think to provide. The chart above answers "yes" to the baseline check with a birth time and "no" without one, a flip that happens to roughly one birthday in nine across the full historical census. Metal day masters, as a group, get the encouraging baseline less often than the other four elements (47.5% versus an overall 57.3%) — a fact the screen itself has never stated. None of this is a verdict on any exam; it's the arithmetic sitting under two sentences that already exist on your screen.