BaZi calculator: your four pillars and five elements
Enter your Gregorian birth date and time to get the four pillars (year, month, day, hour), the Day Master and the five-elements distribution. The chart is calculated locally in your browser — nothing is uploaded — and the rules are the same ones used by the paid report on this site, so the two never disagree.
If you do not know the hour, the chart shows three pillars and leaves the hour pillar empty — it never fills in a placeholder that would look like a real reading.
How this calculator works
The year pillar switches at the Start of Spring, and the month pillar follows the twelve solar terms rather than calendar months. The day pillar comes from the day count, and the hour pillar is derived from the day stem through the Five Rats rule. The five-elements tally counts hidden stems with weights.
Those boundaries are exactly where two BaZi apps tend to disagree. If a chart here differs from another tool, compare the four pillars first — input and boundary rules — before comparing any interpretation that follows.
How to read the four pillars
The year and month pillars come from the solar calendar, not from a clock
The year pillar changes at the Start of Spring (立春), not on 1 January, and the month pillar follows the twelve solar terms rather than the twelve calendar months. Two people born in the same Gregorian month can therefore land in different pillars, and a birth a few days either side of a term can land either side of a month boundary. This calculator places both boundaries by solar longitude and marks a birth that sits within about a day of a term, because that is exactly where two tools with slightly different term tables disagree.
The day pillar is the anchor everything else is read against
The day stem is the Day Master — an element plus yin or yang — and the other three pillars are read relative to it through the ten-god relationships. The five-element distribution is counted across all four pillars including the hidden stems inside each branch, weighted rather than one-per-branch, so a chart with one visible Wood branch does not read as a chart with no Wood at all. A weak element is not the same as a helpful element: weakness describes the structure of the chart, while what actually helps has to be read together with the Day Master and the month.
The hour pillar is the part that depends on your clock
The hour branch is simply the two-hour block your clock time falls into, and the hour stem is derived from the day stem. The only thing that can move it is the calendar day you count from, which is the late-Zi case below. If the birth time is unknown, the honest output is three pillars with the hour left empty — filling in 12:00 would produce a chart that looks complete and is not.
If another chart disagrees, check these three things
First: the month pillar and a term boundary
Month boundaries are solar terms, and term tables differ slightly between tools. If the two charts differ only in the month pillar, compare how each one places the term you were born near, not the birth time itself.
Second: the day pillar and the late-Zi convention
For a birth between 23:00 and midnight, some schools start the next day at 23:00 while others do not. This site keeps the day pillar on the calendar day and starts the Zi hour from that day's stem, and the chart marks the case. A one-day difference in the day pillar almost always comes from this convention, and it changes how the whole chart is read.
Third: the hour pillar and the time you entered
If the hours differ, check whether one of the two used a different clock — the time you type in is used as-is here (Beijing time), with no true-solar-time correction, and the same rule applies to the paid report tool on this site, so the two cannot drift apart on that point. True solar time is a separate decision with a separate table, explained in the site's method notes rather than applied silently.
The full rule list, in one place: which calculation rules to compare first.
What this tool does not do
It does not predict events, does not tell you what to buy, and does not promise that any element will change anything. A weakest element is a description of the chart's structure, not an instruction, and it is not the same thing as a favourable element. Use the chart to check your inputs and to look at your own patterns; use your own judgement for anything that actually costs money or time.
Want the reading written for one specific direction — relationship, work, spending or everyday choices — with the sources shown? That is a HK$29 single-direction report on this site.
Get the HK$29 single-direction reportWhat you get for HK$29, before you pay
One written direction only — relationship, work, spending or everyday choices — with the chart next to it so the reasoning can be checked. The report is delivered in Chinese; payment runs through Stripe in HKD. A free chart on this page already gives you the four pillars, the Day Master and the five-elements distribution.
Keep checking
排盘方法与验证记录（中文） · 不知道出生时辰时能看什么（中文） · 不同平台结果不一样时先核对什么（中文）
English guides: English home · which calculation rules to compare first · how to test a reading before trusting it · Zi Wei chart (same birth data).
· 紫微斗数排盘 · Zi Wei Dou Shu chart（另一套体系） · 小八字中文站