The time on your birth record is what a clock in that room displayed. And that clock was not set to the sun over Seoul. It was set to the sun over Akashi, in Japan.
Korea Standard Time runs on the 135th meridian east. Seoul sits near 127. So if you enter the time on your record exactly as written, is your hour pillar right?
What this article answers
The hour written down is not the hour used
The hour in a Saju chart follows the sun where you were born, not the clock a country agreed on. Inside Korea alone that gap runs from sixteen to thirty-six minutes.
The short answer: an hour is converted, not copied
The slot that carries your birth time is called the hour pillar. What goes into it is not the number written on your record. It is that number converted to the sun where you were born.
The conversion is wider than people expect. Inside Korea it runs from sixteen to thirty-six minutes, and in years with daylight saving another hour sits on top. Since one branch of the day covers two hours, a birth near a boundary can shift a whole slot on this alone.
In one line
The hour on your record is source material. The hour a chart uses is that material converted. They are not the same number.
The hour is one of four pillars
A Saju chart has four pillars: year, month, day and hour. The hour pillar takes one of the twelve branches that divide a day, and since each branch spans two hours, a birth on a boundary moves a whole slot. For the characters themselves, see Heavenly Stems and Earthly Branches.
So how the hour is converted genuinely changes the result. An exact time entered without conversion is wrong, and a conversion made against the wrong reference is wrong too.
Why standard time and solar time diverge
Standard time is an agreement to run a whole country on one meridian. Korea runs on 135 degrees east. But that line does not cross Korean soil — it passes near Akashi in Japan.
The sun moves fifteen degrees an hour, so one degree of longitude is four minutes. Our engine converts with exactly that: correction in minutes = (birth longitude − 135) × 4. Korea lies west of 135, so the value is always negative. The clock runs ahead of the sun.
How many minutes is your city?
People round this to "about thirty minutes in Korea." That holds near Seoul and nowhere else. Below are the longitudes in our city database run through the formula above.
| City | Longitude (east) | Correction |
|---|---|---|
| Sinan (westernmost listed) | 126.108 | −36 min |
| Mokpo | 126.392 | −34 min |
| Jeju | 126.531 | −34 min |
| Incheon | 126.705 | −33 min |
| Gwangju | 126.852 | −33 min |
| Seoul | 126.978 | −32 min |
| Daejeon | 127.385 | −30 min |
| Daegu | 128.601 | −26 min |
| Gangneung | 128.876 | −24 min |
| Busan | 129.075 | −24 min |
| Ulsan | 129.312 | −23 min |
| Ulleung (easternmost listed) | 130.905 | −16 min |
What you get from this
The westernmost and easternmost entries differ by twenty minutes. Two people born at the same clock time, one in Mokpo and one in Ulleung, stand twenty minutes apart by the sun. That is enough to split them at a boundary.
Note that this correction is mean solar time from longitude only. The sun's actual noon drifts further back and forth with the season, and our engine does not fold that in.
The Ja hour, where a day turns over
Births in the 23rd hour are the awkward case, because where the day boundary sits decides the day pillar as well. Schools disagree here, and the terminology is used in opposite senses from one source to the next: some call keeping the pre-midnight hour with the current day one thing, others use the same word for the reverse.
So this article does not declare a winner. It states what our service actually does.
What our service actually does
The input screen carries two Ja-hour settings: a toggle, and a basis that decides whether a branch starts on the hour or on the half hour. The defaults are toggle off and half-hour basis. Here is where the day turns in each case.
| Setting | Where the day turns | A birth at 23:30 |
|---|---|---|
| Ja-hour toggle off (default) | Midnight | A birth at 23:30 keeps that day's day pillar |
| Toggle on, half-hour basis (default) | 23:30 | From 23:30 the day pillar becomes the next day's |
| Toggle on, whole-hour basis | 23:00 | From 23:00 the day pillar becomes the next day's |
What we do not claim
We do not settle which setting is correct. But comparing your result against another site without knowing which setting produced it is where most apparent contradictions come from: not a wrong calculation, a different reference.
Daylight saving, the forgotten hour
Korea has had daylight saving. If you were born during one of those spells, your record shows what a clock running an hour early displayed. Here is what the time zone database returns.
| Period | Summer offset | What it means |
|---|---|---|
| Summers of 1948, 1949, 1950, 1951 | UTC+10 | Daylight saving in force, clocks an hour ahead |
| Summers of 1955 to 1960 | UTC+9:30 | The standard meridian was 127.5 degrees, plus daylight saving |
| Summers of 1987 and 1988 | UTC+10 | Daylight saving in force, clocks an hour ahead |
| Every other period | UTC+9 | Based on 135 degrees east |
For now, subtract it yourself
Our engine does not automatically correct daylight saving for Korean births. If you were born in one of those summers, enter the recorded time minus one hour. Automatic handling is on our list.
A different problem from term boundaries
Reading about birth times, solar terms come up too. They are easy to confuse but move different pillars. Time correction moves the hour; term boundaries move the month and year. The term side is covered in 24 Solar Terms in Saju.
When you do not know your birth time
Records go missing often enough. When you tell our calculator the time is unknown it uses noon as a stand-in and marks the result as time-unknown, rather than inventing something plausible.
The year, month and day pillars still read normally in that case. Interpretations that lean on the hour pillar are better held back. If you want to chase the record down, a birth registration or hospital file is the place to look. For the day pillar itself, see the 60 Ilju guide.
Five sentences for checking your own time
Five checks in order. The right column is the judgment people usually get wrong at that step.
| Step | What to look at | Mistake to avoid |
|---|---|---|
| 1. Find the record | The minute-level time on a birth registration or hospital record | Estimating from memory |
| 2. Settle the birthplace | The town you were born in, not where you grew up | Entering where you live now |
| 3. Read your correction | Your city's value in the table below | Rounding the whole country to thirty minutes |
| 4. Check daylight saving | Whether a summer birth falls in a listed year | Entering the recorded time as-is in a listed year |
| 5. Look at the Ja boundary | A birth in the 23rd hour splits by setting | Comparing results without knowing the setting |
In one sentence
Conclusion
The hour on your record is source material. The hour a chart uses is that material converted to the sun where you were born.
Pick your birthplace and the screen shows how many minutes were applied. Check it against the value you found in the table above.
What we checked
The formula and the per-city values come from reading our own time-handling code and running the real longitudes in our city database through it. The thirty-two minutes for Seoul is the same figure practitioners use. The earlier version's "about thirty minutes" only holds near Seoul, so we replaced it with per-city values.
The daylight saving years were read straight from the time zone database. The Ja-hour behaviour was verified by running the calculator — and in doing so we found that the toggle did nothing under the default settings, fixed it, and the table above reflects the fixed behaviour.
What we did not settle: the direction the Ja-hour terminology points, which is reversed between sources, so we took no side; the equation of time, which we left out of the calculation; and 1954 to 1961, when the standard meridian itself differed so the formula above does not apply cleanly. If Saju is new to you, start with What Is Saju.
Mystic Universe Editorial
Authorship & review
The formula and per-city values come from reading this service's own time-handling code and running the real longitudes in its city database through it. The daylight saving years were queried directly from the time zone database. The Ja-hour behaviour was verified by running the calculator, which surfaced a toggle that did nothing under the default settings; the table reflects the fixed behaviour. We take no side on the reversed Ja-hour terminology, and we state in the article that the equation of time and the 1954-1961 meridian change are not folded into the calculation. This article does not predict career, marriage, lifespan, or wealth from a birth time.
Frequently Asked Questions
Q.Can I get a reading without knowing my birth time?▾
Yes. When the time is unknown this service uses noon as a stand-in and marks the result as time-unknown. The year, month and day pillars read normally; only interpretations that lean on the hour pillar should be held back. That is better than inventing a plausible time. To chase the record down, try a birth registration or hospital file.
Q.What are Yaja-si and Joja-si?▾
They name a disagreement about where the day boundary sits for births in the 23rd hour. The trouble is that sources use the terms in opposite senses, so this article takes no side. Instead it states what this service does: the Ja-hour toggle is off by default, and turning it on moves the day pillar to the next day from 23:30 local clock time, or from 23:00 on the whole-hour basis.
Q.What is true solar time correction?▾
Standard time runs on 135 degrees east while Korea sits west of that line, so the clock runs ahead of the sun. The formula is (birth longitude − 135) × 4 minutes, which gives −32 minutes for Seoul. The common shorthand of 'thirty minutes in Korea' only holds near Seoul; city by city it ranges from −16 to −36 minutes.
Q.What do I enter if I was born during daylight saving?▾
Enter the recorded time minus one hour. This service does not currently apply daylight saving automatically for Korean births. The affected spells are the summers of 1948-1951, 1955-1960, and 1987-1988. Automatic handling is on our list.
Q.I was born just after midnight, so why is no correction applied?▾
When applying the correction would push the date to the previous day, this service cancels it and keeps the original time. For Seoul that covers births between 00:00 and roughly 00:32. The behaviour avoids crossing a day boundary and changing the day pillar as a side effect.
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