What do you enter in the saju calculator?
The form above asks for four things, and each one feeds a different part of the calculation.
| Field | What to enter | What it decides |
|---|---|---|
| Year, Month, Day | Your birth date in the Gregorian calendar, from 1900 to the current year | The year, month and day pillars |
| Hour, Minute | The time the clock showed at birth, on the 24-hour clock; or check "Birth time unknown" | The hour pillar, which side of a solar-term boundary the birth falls on, and whether the day pillar moves to the next day |
| Birthplace | The nearest city in a list of about 450, or "Not listed (choose a time zone)" | The longitude turns clock time into true solar time, and the time zone gives the UTC offset and daylight saving time in force at birth |
| Gender | Female or Male | Only the direction of the 10-year luck cycles |
Enter the time exactly as the clock showed it, so that 2:30 p.m. is hour 14 and minute 30. Do not adjust it for daylight saving time yourself. The calculator does that from the birthplace and the date.
If you check "Birth time unknown", the chart has three pillars and six characters, and the hour column reads "Time unknown". The year and month pillars are then taken as of noon at the birthplace. If the birthday is a day on which the saju month changes, the page shows both possible pairs of year and month pillars. Entered without a time, the example above keeps its year, month and day pillars, 乙亥, 己卯 and 乙巳, loses its hour pillar 癸未, and has the starting age of its luck cycles marked as approximate.
The Birthplace list holds about 450 cities in 188 countries, with longitudes and time zones from GeoNames. If your city is missing, pick the nearest one listed: true solar time shifts by four minutes for each degree of longitude between the two places. If no listed city is near, choose "Not listed (choose a time zone)" and select the zone by its IANA name, such as America/Anchorage. The chart then uses standard clock time with no longitude correction, and if daylight saving time was in effect at birth, that hour is taken off first. The first line under "How this chart was calculated" states which basis was used.
Gender changes one thing: whether the 10-year luck cycles run Forward or in Reverse. Entered as male, the example birth keeps the same eight characters, but its cycles run in Reverse and the first one starts at age 3.1, in 1998, instead of at age 7, in 2002.
Which rules does this saju calculator follow?
Two saju calculators can draw different charts from the same birth, because they can differ on four points: when the year starts, when a month starts, when a day starts, and which clock is read. The table gives this calculator's rule on each point next to alternatives you may meet elsewhere.
| Point | This calculator | Common alternatives |
|---|---|---|
| Start of the year | The instant of Ipchun (입춘, 立春, the Beginning of Spring), around February 4 | January 1, or Lunar New Year |
| Start of a month | The instant of each of the 12 solar terms called jeol (절, 節), from Ipchun to Sohan (소한, 小寒, Minor Cold) | The first day of each lunar month |
| Start of the day | 23:00, when the hour of the Rat (子) begins | Midnight, with the hour of the Rat split into a late-night half and an early-morning half |
| Time basis for the day and hour | True solar time at the birthplace | Standard clock time, read as it stands |
The year and month pillars follow the solar terms, not the dates on a wall calendar. The Encyclopedia of Korean Culture, in its entry on saju, says that in this practice the new year begins at Ipchun, so that a person born after Lunar New Year but before Ipchun still takes the year pillar of the old year. It also says that a month changes at the start of its solar term and not on the first of the month. In 1995, Lunar New Year fell on January 31 and Ipchun on February 4. A birth in Seoul at noon on February 1, 1995 gets the year pillar 甲戌, and one at noon on February 5 gets 乙亥.
A solar term is an instant, not a whole day. The Hong Kong Observatory describes the 24 solar terms as dividing the ecliptic, the sun's yearly path among the stars, into 24 equal segments of 15 degrees of the sun's longitude. Twelve of the 24 are jeol and start a saju month. The twelve between them change nothing in the chart. The calculator turns the birth into an absolute instant and compares it with the instant of the term to the minute, so the same moment of birth lands on the same side of a boundary in every time zone. The term instants come from the open-source lunar-typescript library.
Practitioners differ on when the day changes. The Encyclopedia of Korean Culture records that some split the hour of the Rat into yajasi (야자시, 夜子時, 23:00 to 0:00) and jeongjasi (정자시, 正子時, 0:00 to 1:00) and set the day pillar accordingly, and that some shift the dividing line by location, to 0:32:47 in Seoul. This calculator does not split the hour. Once the time used for the chart reaches 23:00, the day pillar is that of the next day, and a note under the chart says so.
The page on how saju and BaZi conventions differ goes through these choices one at a time. The About and method page gives every rule, with the solar-term times and the known limits. One of those limits is that births in both hemispheres get the same solar-term months.
Why does the chart use true solar time instead of clock time?
This calculator sets the day and hour pillars by the position of the sun, which a clock does not show directly. A clock shows one standard time for a whole time zone. True solar time is the time a sundial at the birthplace would show. It differs from clock time in two ways, both set out in the U.S. Naval Observatory's explanation of the equation of time. Solar time moves four minutes for each degree of longitude between a place and the meridian that defines its time zone. And the sun runs ahead of or behind its yearly average by as much as 16 minutes, a seasonal gap called the equation of time.
In the example above, the clock time 14:30 becomes 13:48. Seoul lies about 8 degrees west of the 135°E meridian that UTC+9 is based on, which takes off 32 minutes, and the equation of time in mid-March takes off another 10. The corrected time falls in the 未 (Sheep) hour, which runs from 13:00 to 14:59, so the hour pillar is 癸未. The correction matters most near a boundary. A birth at 15:20 on the same day in Seoul was at 14:38 by the sun and also gets 癸未, though read by clock time it would fall in the 申 (Monkey) hour.
The same clock reading means a different solar time in each city. The table shows a birth at 12:00 on July 1, 2000 as the calculator converts it for seven places in the Birthplace list.
| Birthplace | UTC offset in force | Correction | True solar time | Hour pillar |
|---|---|---|---|---|
| Seoul, South Korea | UTC+9 | −36 minutes | 11:24 | 壬午 |
| New York City, NY, United States | UTC−4, daylight saving time | −60 minutes | 11:00 | 壬午 |
| Los Angeles, CA, United States | UTC−7, daylight saving time | −56 minutes | 11:04 | 壬午 |
| London, United Kingdom | UTC+1, daylight saving time | −64 minutes | 10:56 | 辛巳 |
| Madrid, Spain | UTC+2, daylight saving time | −138 minutes | 09:42 | 辛巳 |
| Singapore, Singapore | UTC+8 | −68 minutes | 10:52 | 辛巳 |
| Sydney, NSW, Australia | UTC+10 | +1 minute | 12:01 | 壬午 |
In London, Madrid and Singapore the corrected time falls before 11:00, so the hour pillar is 辛巳 and not 壬午.
The UTC offsets come from the IANA Time Zone Database, which records the history of local time around the world, including changes to UTC offsets and daylight saving rules. That is why a summer birth needs no adjustment by hand. When daylight saving time was in effect, a note under the chart says so.
How do you read the four pillars table?
The table under "Your four pillars" has four columns. From left to right they are the Hour pillar, the Day pillar, the Month pillar and the Year pillar, so the birth is read from right to left: year first, hour last. Each column has six rows.
| Row | What it shows | In the example (hour, day, month, year) |
|---|---|---|
| Ten god, first row | How the stem of that pillar relates to the Day Master; the day column reads "Day Master" | Pyeonin (Indirect Resource), Day Master, Pyeonjae (Indirect Wealth), Bigyeon (Friend) |
| Heavenly Stem | The upper character of the pillar, with its Korean reading, yin or yang, and element | 癸 gye Yin Water, 乙 eul Yin Wood, 己 gi Yin Earth, 乙 eul Yin Wood |
| Earthly Branch | The lower character, with its Korean reading, animal and element | 未 mi Sheep Earth, 巳 sa Snake Fire, 卯 myo Rabbit Wood, 亥 hae Pig Water |
| Ten god, second row | How the branch of that pillar relates to the Day Master | Pyeonjae (Indirect Wealth), Sanggwan (Hurting Officer), Bigyeon (Friend), Jeongin (Direct Resource) |
| Hidden stems | The one to three stems that each branch contains | 丁 乙 己, 戊 庚 丙, 乙, 戊 甲 壬 |
| Life stage | Where the Day Master stands in a twelve-stage cycle at that branch | Nurture, Bath, Prime, Death |
Read downward, each column is one pillar: a Heavenly Stem (cheongan, 천간, 天干) on top of an Earthly Branch (jiji, 지지, 地支). The example's pillars are 乙亥 for the year, 己卯 for the month, 乙巳 for the day and 癸未 for the hour. The Encyclopedia of Korean Culture explains the name saju (사주, 四柱, "four pillars") as a picture of a person as a house whose four pillars are the year, month, day and hour of birth. Each pillar is written with two characters, eight in all, so the chart is also called palja (팔자, 八字, "eight characters"). The page on what saju is covers that background.
Each stem also has a color and each branch an animal. That is how the example's year pillar 乙亥 comes to be called the Blue Pig and its day pillar 乙巳 the Blue Snake, as the page on Korean zodiac color animals explains.
The life stages are twelve positions in a cycle named after the course of a life, from Birth to Nurture. A stage such as Death, which the example has in its year column, names a position in that cycle and says nothing about events.
Under the table, "How this chart was calculated" records how the birth time was handled. For the example it reads: "True solar time at the birthplace was 42 min earlier than the clock time, so the day and hour pillars use the corrected time."
What do the sections under the chart mean?
Six sections follow the table. The next table gives the example's result in each one and the rule behind it. The step-by-step guide to reading a saju chart takes the same sections in a fixed order, starting from the Day Master.
| Section | Result for the example | Where it comes from |
|---|---|---|
| Your Day Master (ilgan) | 乙, Yin Wood, "the vine and the flower"; type Spring Flower | The stem of the day pillar. The type pairs it with the season of the month branch, 40 types in all. |
| Five elements (ohaeng) | Wood 3, Fire 1, Earth 2, Metal 0, Water 2; Wood is Abundant and Metal is Missing | A count of the eight characters by element. Hidden stems are not counted. |
| Day Master strength | Slightly strong, Level 5 of 7, Score 58 | Three checks, In season, Rooted and Supported, and a score of the support found in each pillar |
| Ten gods (sipseong) | Bigeop (Companions) 2, Siksang (Output) 1, Jaeseong (Wealth) 2, Gwanseong (Officer) 0, Inseong (Resource) 2; "The independent type" | Each of the other seven characters, named by its element and yin-yang relative to the Day Master |
| Special stars (sinsal) | Bokseong Gwiin (Fortune Star), Geumyeo (Golden Carriage), Yeokma (Traveling Horse), Hwagae (Canopy Star) | Fixed lookups: most noble stars from the Day Master, the other three stars from the year branch and the day branch |
| 10-year luck cycle (daeun) | Forward; first cycle 庚辰, from age 7, in 2002 | Direction from the yin-yang of the year stem and the gender. Starting age from the days to the neighboring jeol, three days to a year. |
The Day Master (ilgan, 일간, 日干) is the Heavenly Stem of the day pillar. It stands for the person the chart belongs to, and every other section is read against it. The example's Day Master is 乙 (eul), Yin Wood, which the tradition pictures as a vine or a flower. Its month branch 卯 belongs to spring, so its type is Spring Flower. The Day Master guide describes all ten.
Five elements (ohaeng, 오행, 五行) counts how many of the eight characters belong to Wood, Fire, Earth, Metal and Water. An element with none is marked Missing and one with three or more is marked Abundant, each with a short note on how the tradition reads it. The example has no Metal and three Wood characters: the stems 乙 of the year and day pillars and the branch 卯 of the month pillar.
Day Master strength rates how much support the Day Master gets from the rest of the chart, on seven levels from Very weak to Very strong. Strong (singang, 신강, 身強) and weak (sinyak, 신약, 身弱) describe balance, not good or bad. The example passes two of the three checks, In season (deukryeong) and Supported (deukse), and fails Rooted (deukji). It is rated Slightly strong. The "Score by pillar" table shows how much each pillar adds to the score, and in the example the month pillar adds the most.
The ten gods (sipseong, 십성, 十星) are ten names for the way every other character in the chart relates to the Day Master. They are not deities. The section lists the god at each position, counts them in five groups and prints the traditional reading for the largest group. In the example, Companions, Wealth and Resource tie at two each. A tie goes to the group that comes first in the list, so the page shows "The independent type".
Special stars (sinsal, 신살, 神殺) are set patterns between particular stems and branches. The calculator checks 16 noble stars (gwiin, 귀인, 貴人) and three others: Dohwa (Peach Blossom), Yeokma (Traveling Horse) and Hwagae (Canopy Star). Each star found is listed with the pillar it sits in. The example has Bokseong Gwiin in the year pillar, Geumyeo in the day pillar, Yeokma in the year and day pillars, and Hwagae in the hour pillar. When a chart has none, the section says so.
Daeun (대운, 大運) are ten-year periods that follow on from the month pillar. The Encyclopedia of Korean Culture describes daeun as the part of a reading that shifts in ten-year units, alongside seun (세운, 歲運), which shifts year by year. In the example the year stem 乙 is yin and the gender is female, so the cycles run Forward. The next jeol after the birth, Cheongmyeong (청명, 清明) on April 5, came about 21 days later, which at three days to a year gives a start at age 7. The first cycle, 2002–2011, is 庚辰, the pillar after the month pillar 己卯, and the section lists ten cycles with the ten god of each.
What does this calculator not do?
| It does not | What it does instead |
|---|---|
| Use AI to produce the chart or the text | The pillars, ten gods, stars and luck cycles come from a fixed algorithm and calendar data. The descriptions are fixed texts matched to the result, so the same input always returns the same page. |
| Predict events | Each section says what the saju tradition reads into a feature of the chart. Nothing on the page states what is going to happen. |
| Store your birth details | They are sent to the server only to compute the chart and are not stored. Your input stays in the page address after the #, so you can reopen the same chart. |
| Compare two people | It reads one chart at a time. Two charts are compared by the saju compatibility calculator. |
Saju is a traditional practice, not a science. The chart shows how that tradition reads a birth time, and it is offered for cultural interest and self-reflection.
This site calls no AI service. If you want an AI assistant to interpret your chart, the ChatGPT saju prompt page computes the chart by the same rules and gives it to you as text to paste, so the assistant starts from the right pillars. How your input is handled is set out on the privacy page.