Why compute the saju chart before asking an AI to read it?
A saju reading is two jobs, and they call for different tools. The first job turns a moment of birth into eight characters. The second explains those characters in words. The Encyclopedia of Korean Culture defines saju (사주, 四柱, "four pillars") as the year, month, day and hour of birth, each written with one of the ten Heavenly Stems and one of the twelve Earthly Branches. Four pairs make eight characters, which is why a chart is also called palja (팔자, 八字, "eight characters").
The first job is calendar arithmetic, not interpretation. The same encyclopedia entry gives the rules. The year starts at Ipchun (입춘, 立春, the Beginning of Spring). A month changes when its solar term begins, not on the 1st. The day pillar is copied from the manseryeok (만세력, 萬歲曆), the almanac that lists the stem and branch of every day. Each rule is a lookup in dated calendar data, not a matter of judgment. The table sets out what each part of a chart depends on, as this site's calculator computes it.
| Part of the chart | Where it changes | What the calculation needs |
|---|---|---|
| Year pillar | At Ipchun, around February 4. Not on January 1 and not at Lunar New Year. | The date and minute of Ipchun in the birth year |
| Month pillar | At each of the 12 solar terms called jeol (절, 節), from Ipchun to Sohan (소한, 小寒, Minor Cold) | The date and minute of the jeol on either side of the birth |
| Day pillar | At 23:00 true solar time, when the 子 (Rat) hour begins | The position of the day in the 60-pillar cycle, and true solar time at the birthplace |
| Hour pillar | Every two hours, on the odd hours: 子 is 23:00–00:59, 丑 is 01:00–02:59, and so on | The longitude of the birthplace, the equation of time, and the time zone and daylight saving rules in force on that date |
| 10-year luck cycles (daeun, 대운, 大運) | The starting age comes from the days between the birth and the neighboring jeol, with three days counting as one year | The same jeol instants. The direction comes from the yin-yang of the year stem and the gender. |
A solar term is an instant, not a day. The Hong Kong Observatory defines the 24 solar terms by the Sun's position: they divide its yearly path into 24 equal segments, with 15 degrees of the Sun's longitude between one term and the next. Ipchun, which the observatory lists as "Spring Commences", is the point at 315 degrees. The Sun reaches that point at one moment, and clocks in different time zones show different times for it.
Ipchun in 2026 shows how much rides on that moment. The 2026 calendar data of the Korea Astronomy and Space Science Institute (KASI) puts Ipchun at 05:02 on February 4, Korean time. In this site's calculator, a birth in Seoul at 04:50 that morning gets the year pillar 乙巳 and the month pillar 己丑. A birth at 05:10 gets 丙午 and 庚寅. The two births are 20 minutes apart, and four of their eight characters differ. The calculator compares births and solar terms as absolute instants, to the minute. A birth in Los Angeles at 12:10 on February 3, 2026, is the same moment as 05:10 in Seoul, so it also gets 丙午 and 庚寅, although the local date is still February 3.
The day and hour pillars take a second conversion, from clock time to true solar time, which is the time a sundial at the birthplace would show. The U.S. Naval Observatory describes the two parts of the gap. Solar time differs from clock time by 4 minutes for each degree of longitude between a place and the defining meridian of its time zone. The equation of time, a seasonal difference between sundial time and clock time, can reach about 16 minutes. In the example above (born March 15, 1995, at 14:30 in Seoul), true solar time was 42 minutes earlier than the clock. The pillars are set from 13:48, which is still in the 未 (Sheep) hour, 13:00–14:59, and the hour pillar is 癸未. The size of the correction depends on the city: on the same date, the calculator moves a Los Angeles birth 3 minutes earlier and a Madrid birth 84 minutes earlier.
Clock time has a history as well. The calculator takes past time-zone offsets and daylight saving time from the IANA Time Zone Database, which records daylight saving time in South Korea in 1987 and 1988. A birth entered as 14:30 on July 1, 1988, in Seoul comes out 96 minutes earlier in true solar time: an hour for daylight saving time, 32 minutes for Seoul's longitude and the rest for the equation of time. That is 12:54, in the 午 (Horse) hour, and the hour pillar is 丙午. Taken straight from the clock, 14:30 would fall in the 未 (Sheep) hour and give 丁未.
Every step above is a lookup or a sum, and an error in any of them changes the characters that the whole reading rests on. This page therefore splits the work. The calculator sets the pillars with a fixed algorithm and no AI model, so the same birth details always give the same chart. The assistant receives the finished chart and does the part that is language: explaining what the tradition reads into each feature. The first paragraph of the prompt says, "Please do not recompute the pillars. Use them exactly as given." Every conversation then starts from the same eight characters, and any reply can be checked against the chart on this page. Calculators do not all follow the same conventions for time, and the page on how saju and BaZi conventions differ lists the alternatives.
How do I use the saju prompt in ChatGPT?
- Fill in the form above: the year, month and day of birth in the Gregorian calendar, the birth time, the birthplace and the gender. Enter the time the clock showed, without adjusting for daylight saving time yourself. If the time is not known, check "Birth time unknown".
- Press "Calculate chart". The text under "Ask an AI assistant about your chart" changes from the example to your own chart.
- Press "Copy request". The button reads "Copied" once the text is on the clipboard.
- Open ChatGPT or the AI assistant you normally use, start a new conversation, paste the whole text and send it. There is no need to type the birthday again or to reword anything.
- Compare the pillars in the reply with the "Your four pillars" table on this page. For the example they are year pillar 乙亥, month pillar 己卯, day pillar 乙巳 and hour pillar 癸未. If a character differs, ask the assistant to go back to the pillars as pasted.
The prompt has four parts: a statement that the chart was computed by a calculator, a list of five topics to cover, a request about how to explain them, and the chart itself. The five topics run from the Day Master (ilgan, 일간, 日干), which is the stem of the day pillar, to the current 10-year luck cycle (daeun). The first three parts are a fixed template. Only the chart lines change with what you enter, and no part of the text is generated by an AI model.
What is in the prompt, line by line?
Each chart line in the prompt matches one section of the result. The table uses the values of the example above.
| Line in the prompt | In the example above | What it is |
|---|---|---|
| Birth | March 15, 1995, 14:30, Seoul, South Korea, Female | The birth details as entered |
| Year pillar, Month pillar, Day pillar, Hour pillar | 乙亥, 己卯, 乙巳, 癸未 | The four pillars, each with the element of its Heavenly Stem and the animal of its Earthly Branch |
| Day Master and Strength | 乙 (Yin Wood); Slightly strong | The Day Master (ilgan) is the stem of the day pillar. Strength is rated on seven levels. |
| Five elements | Wood 3, Fire 1, Earth 2, Metal 0, Water 2 | How many of the eight characters belong to each element |
| Ten gods | Seven entries, from "Year pillar Heavenly Stem 乙: Bigyeon (Friend)" to "Hour pillar Earthly Branch 未: Pyeonjae (Indirect Wealth)" | The relation of each of the other seven characters to the Day Master |
| Special stars | Bokseong Gwiin (Fortune Star), Geumyeo (Golden Carriage), Yeokma (Traveling Horse), Hwagae (Canopy Star) | The noble stars and other special stars found in the chart |
| 10-year luck cycles (daeun) | Forward, first cycle from age 7; ten cycles from 2002–2011 庚辰 to 2092–2101 己丑 | The ten-year periods that follow on from the month pillar |
| Method | Korean saju rules. The year changes at Ipchun (the start of spring) and months change at the solar terms. | The rules behind the year and month pillars, set out in full on the About and method page |
| Last line or lines | True solar time at the birthplace was 42 min earlier than the clock time, so the day and hour pillars use the corrected time. | How the birth time was handled for this chart |
The prompt carries a summary of the result, not all of it. It leaves out the hidden stems, the life stages, the strength score and its three checks, and the ten god of each luck cycle. The saju calculator on the home page shows every section for the same birth details.
What do the last lines of the prompt say about the birth time?
The prompt ends with the same notes that appear under "How this chart was calculated" below the pillar table. The first note is one of three sentences, depending on what was entered. It tells the assistant which kind of time the day and hour pillars were set from.
| What was entered | The line begins | How the chart was computed |
|---|---|---|
| A birthplace from the list and a birth time | "True solar time at the birthplace was…" | Clock time was converted to true solar time with the longitude of the place and the equation of time. The line gives the size of the correction in minutes and says whether solar time was earlier or later than the clock. The day and hour pillars use the corrected time. |
| "Not listed (choose a time zone)" and a birth time | "No longitude is known for this birthplace…" | Standard clock time in the chosen time zone was used, with no true solar time correction. If daylight saving time was in effect at the birth, that hour is taken off first. |
| "Birth time unknown" | "The birth time is unknown…" | The chart is built from the date alone. It has no hour pillar, and the year and month pillars are taken as of noon at the birthplace. |
After that first note, the prompt adds a further line for each special condition that applies to the chart.
| The extra line begins | When it appears |
|---|---|
| "Daylight saving time was in effect at this birth time…" | Clocks were on daylight saving time at the birth, and the calculation accounts for the extra hour |
| "The time you entered did not exist on that day…" or "The time you entered happened twice that day…" | The time fell in the hour that was skipped or repeated when the clocks changed; the line says how it was read |
| "The time used for the chart is after 23:00…" | The 子 (Rat) hour had begun. The calculator starts a new day at 23:00, so the day pillar belongs to the day that begins then |
| "If the birth came on the other side of the solar term…" | The birthday is a solar-term day and the birth time is unknown; the line names the other possible year and month pillars |
The last row is the one case in which the year and month pillars are not certain. For a birth in Seoul on February 4, 2026, with no time, the prompt lists 丙午 and 庚寅, the pillars as of noon, and ends: "If the birth came on the other side of the solar term: year pillar 乙巳, month pillar 己丑."
Two other details change with the input. When the birthplace is not in the list, the Birth line shows the name of the time zone, such as Asia/Seoul, in place of a city. When the birth time is unknown, the Birth line reads "Birth time unknown", there is no Hour pillar line, and the ten gods line has five entries instead of seven.
Which follow-up questions work well?
The prompt asks the assistant to cover five topics first. After that, ask about one thing at a time and name the line the answer should rest on. Each answer can then be checked against the chart. The questions in the table use the values of the example; replace them with the characters in your own chart.
| What you want to know | A question to ask | Line it rests on |
|---|---|---|
| Whether the assistant took in the chart | "Before you explain anything, list the four pillars you received, all eight characters." | Year pillar to Hour pillar |
| The image of the Day Master | "What image does the tradition use for a 乙 Yin Wood Day Master? Answer from the Day Master line only." | Day Master |
| Strength | "How is a Slightly strong Day Master traditionally read, and how does it differ from Balanced and from Strong (singang)?" | Strength |
| Plenty and lack among the elements | "My chart has Wood 3 and Metal 0. Which ways of reading that does the tradition offer?" | Five elements |
| Ten gods | "The chart has two Bigyeon (Friend), two Pyeonjae (Indirect Wealth) and no Gwanseong (Officer) stars. How is that mix traditionally described?" | Ten gods |
| Special stars | "What do Bokseong Gwiin and Geumyeo traditionally stand for?" | Special stars |
| The current luck cycle | "For a 乙 Day Master, which ten god is 壬, the stem of the 2022–2031 cycle 壬午?" | 10-year luck cycles (daeun) |
| Where schools differ | "Do different schools read this point differently? List the views separately and mark anything that is your own guess." | Any line |
| A plainer version | "Rewrite your explanation in under 150 words, without technical terms." | The whole reply |
Some answers can be checked against this site. For the 壬午 cycle of the example, the luck-cycle table on the home page gives Jeongin (Direct Resource). When an assistant's answer differs from the site, check first that it quoted the characters as pasted, and only then ask whether the difference is one between schools. The step-by-step guide to reading a saju chart gives the usual reading order, from the Day Master to the luck cycles.
How do I ask about two charts (gunghap)?
Gunghap (궁합, 宮合) is the saju word for compatibility between two charts, so it takes two charts. This page computes one person at a time. Compute twice and paste twice.
- Calculate your own chart, copy the request and paste it into a new conversation.
- Return to this page, enter the other person's birth details, press "Calculate again" and copy the request once more.
- In the same conversation, write: "Here is a second person's chart. Compare the two Day Masters and the two day branches, and describe how the elements of each chart complement the other." Then paste only the chart lines, from "Birth:" down.
The saju compatibility calculator makes the same comparison by fixed rules. It checks the combination of the two day stems, the relations between the branches and how the elements of each chart complement the other, and it returns a gunghap score from 50 to 100 with the reasons. Paste the lines under "Why this score" to the assistant and ask what each one traditionally means. The reply then has named items to check.
What should I keep in mind when an AI reads my saju?
An assistant's reading is an interpretation, not a verdict. Saju is a traditional practice, schools read the same chart in different ways, and two replies to the same prompt need not match in wording or emphasis. That is why the prompt asks for a descriptive reading: what each feature is traditionally taken to mean, with no prediction of specific events. Keep that paragraph when you paste.
The characters in the prompt are the reference. If a reply shows a stem, a branch, a ten-god name or a luck-cycle year that differs from what was pasted, ask for a correction before going on.
Share no more personal data than the reading needs. The Birth line holds the birth date, time, place and gender. A reading does not need a name, an address, a phone number or an ID number, so do not add them. To keep the birthday out as well, delete the Birth line before pasting. The other lines are results that have already been computed, although the luck-cycle years still show roughly when the person was born. Before pasting someone else's chart, ask that person. Each AI service sets its own rules for keeping and using conversations, so look at the privacy settings of the service before pasting. What this site does with the details typed into the form is set out on the privacy page.
The limits of the birth details carry over into the reading. With no birth time, the chart has three pillars and six characters, and the assistant has no hour pillar to read. A recorded time that is a few minutes off can change the hour pillar when the birth is close to a two-hour boundary. When the birthplace is not in the list and a time zone is chosen instead, the chart uses standard clock time without the true solar time correction, and the last lines of the prompt say so.