What do you need before you calculate BaZi?
Four pieces of information carry everything the calculation uses. Gather them from the birth record before you open the form.
- The birth date, exactly as the record writes it.
- The calendar that record uses: solar (Gregorian) or lunar, and for a lunar date, whether it falls in a leap month.
- The birth time as precisely as it is written, or a note that it is unknown.
- The place of birth, which decides the time zone.
If you have more than one source, note which details are firm, which come from memory, and which source you used. A date from a document and an hour a relative remembers carry different weight. When a better record turns up, you will know which line to update.
If you have never seen a chart, read what is BaZi first; this page stays with the inputs.
Follow along with the free tool.
Try the BaZi toolHow do you enter a lunar birthday?
The same numbers name a different day in the other calendar, so a lunar birthday typed into the solar fields points to another date and another chart. Choose the calendar the record was written in, and select Leap month when the record marks one.
| The record says | Choose in the form |
|---|---|
| A solar (Gregorian) date | Solar (Gregorian) calendar |
| A lunar date | Lunar calendar |
| A lunar date in a leap month | Lunar calendar, with Leap month selected |
| You are not sure which calendar | Find out before calculating; a guess can give a different day |
Exact time, two-hour period or unknown?
The form asks how precise the recorded time is, with three options: Exact clock time, Two-hour period (shichen) and Birth time unknown. A two-hour period is the traditional division of the day into twelve parts. Choose what the record supports, not what you hope is true.
| The record says | Choose | You get |
|---|---|---|
| A clock time such as 10:20 | Exact clock time | Four pillars |
| A two-hour period such as Si (巳) | Two-hour period (shichen) | Four pillars |
| Only “in the morning” | Birth time unknown, with the range written down separately | Three pillars and the day master |
“In the morning” spans several periods, so it does not name one. The standard periods run two hours each: Si covers 09:00 to 11:00 and Wu covers 11:00 to 13:00, the same division the Hong Kong Observatory lists.
Which time zone should a BaZi chart use?
The birth time zone belongs to the place of birth, not to where you live now. The form asks for an IANA name such as Asia/Seoul and derives that zone's historical UTC offsets and daylight-saving rules from it.
- A local time that happened twice, because the clock moved back: choose the first or the second occurrence, each shown with its UTC offset.
- A local time that never existed, because the clock moved forward: the form refuses it, so check the record.
- Coordinate correction, if you want it: decimal latitude and longitude only, with no city lookup. The preview shows the true-solar-time shift in minutes, flags a change of day or two-hour period, and waits for you to confirm.
How to check the result against its receipt
Enter the details
Type the record into the free BaZi calculator with the calendar, precision and zone you chose above.
Open the receipt
Open the calculation receipt. It lists the conditions the calculation actually used, starting with the input record.
Check the settings
Compare the calendar conversion, time precision, IANA time zone, UTC offset used and any coordinate correction with your notes.
Read the pillars
Only then read the year, month, day and hour pillars. With unknown time, confirm that the result is titled Three pillars (birth time unknown) and shows no hour pillar.
Look at the elements last
The five-element percentages appear only with all four pillars. Read BaZi five elements before treating a large or small share as something about you.
Once the receipt matches your notes, the calculation is done. For the order in which to read the rest, continue with how to read a BaZi chart.
Keep each result with its inputs
Save each result together with the conditions that produced it. The calculator does not keep your birth details for you, so copy the calculation receipt and add a short record like this one.
Chart record
- Date, and where it comes from (document or memory):
- Calendar, and leap month if any:
- Time, and its precision:
- Birthplace time zone and UTC offset:
- Coordinate correction: used or not
- Result: four pillars, or three pillars and the day master
- Calculation receipt: saved
Keep each trial of another time or correction as a separate version, so the reason for any difference stays visible. The chart is the result of those inputs; it does not settle a life decision. The chart is free; AI questions have separate limits. For the terms you meet next, start from the BaZi guide.
Calculating BaZi: common questions
Can I calculate BaZi without a birth time?
Yes. Choose Birth time unknown. The result shows the year, month and day pillars and the day master; the hour pillar and five-element totals are left out. The internal noon anchor is not a birth time. Recalculate when a reliable time becomes available, especially near a solar-term or day boundary.
How do I calculate BaZi from a lunar birthday?
Choose Lunar calendar and enter the date as the record writes it, with Leap month selected if it says so. The same numbers in the solar fields name another day.
Should the time zone be where I live now?
No. Use the birthplace time zone. The zone your browser detects reflects where the device is now, so compare it with the birth record first.
Does true solar time correction change my chart?
Only if you choose it. The preview shows the shift in minutes and flags a change of day or two-hour period, which can change a pillar. Nothing applies until you confirm.
Sources and scope
- Multifate BaZi calculator: Used to check the input fields, the calculation receipt, the four pillars and day master, the element display, and what an unknown-time result leaves out.
- Hong Kong Observatory: Heavenly Stems and Earthly Branches: A calendar reference explaining stem and branch notation for years, months, days and hours, including the traditional two-hour periods.
