How we calculate your chart

The year starts at Li Chun 立春

Our year pillar changes at the exact moment of Li Chun, the Start of Spring, which usually falls on February 3, 4 or 5. It doesn’t change on January 1st or at Lunar New Year. A birth at exactly that moment counts in the new year.

Most zodiac calendars switch animals at Lunar New Year, which can land anywhere from late January to about February 20. If you were born between the two dates, the two systems give you different animals, and we’ll point that out.

Months follow the solar terms 节气

Each BaZi month begins at the exact moment of one of the twelve “jie” solar terms. We convert your birth time to universal time and compare it with those moments, so a birth close to a boundary lands in the right month wherever you were born. A birth right on a term counts in the new month.

We take solar-term moments from the lunar-javascript library and have cross-checked them against an independent astronomy library (astronomy-engine). Across 184 terms the two agree to within a minute, so if you were born within a couple of minutes of a term, we tell you and show the chart on each side.

True solar time, by default 真太阳时

By default we work out your day and hour pillars from true solar time at your birthplace. We take the gap between your birthplace’s longitude and your time zone’s standard meridian (4 minutes per degree) and add the equation of time, because the sun runs up to about 16 minutes fast or slow over the year.

Some practitioners use clock time instead. You can switch to that under Advanced options, and we’ll use your birthplace’s standard time with daylight saving taken out. Both approaches are well established, and your result always says which one it used.

Our equation of time and city coordinates are good to about a minute. If your birth falls within a couple of minutes of an hour or day boundary, we flag that too.

Time zones and daylight saving 时区与夏令时

We convert your birth time using your birthplace’s actual UTC offset at that moment. That comes from the IANA time zone database, which records historical clock changes around the world.

If the clocks went back and your birth time happened twice, we tell you and show whether the second one changes your chart. If the time you entered never existed because the clocks jumped forward, we ask you to double-check it. The database is very good but not perfect for every place and date, especially before 1970.

The Zi hour 子时

By default the new day starts at 11pm, the start of the Zi hour, measured in whichever time your chart uses (true solar time unless you switch it off). From then on, a birth takes the next day’s day pillar, and its hour pillar is counted from that day too.

The other option changes the day pillar at midnight, again in the time your chart uses. For births between 11pm and midnight, the day pillar stays on the current day, but the hour pillar’s stem is counted from the next day’s stem. This is known as the “late Zi hour” approach, and you can pick it under Advanced options.

Unknown birth time 时辰不详

We don’t quietly assume noon. Without a birth time, the hour pillar stays blank. Your year, month and day pillars can depend on the time as well, if Li Chun or another solar term falls on your birth date or the day boundary (11pm or midnight) splits it. When that happens, we list every possibility with the clock times each one covers, to the minute. We show the one covering the longest stretch of the day in full, which doesn’t make it more likely to be yours.

The element count 五行统计

The free chart counts how many of your characters belong to each element: every stem plus each branch’s main element, one point apiece (six characters if you don’t know your birth time). It leaves out hidden stems and seasonal strength, so the element that appears most isn’t necessarily the strongest. An element that doesn’t appear isn’t necessarily missing from your chart either, and this count alone can’t tell you whether you need more of it.

Day Masters are pictures to reflect on 日主意象

We describe each Day Master with a traditional image, like the Oak, the Candle or the Rain. They’re a starting point, a bit like a sun sign. They aren’t a complete personality reading.

What the yearly pages look at 流年页面

Our free yearly pages look at one thing: how your year animal’s branch relates to the year’s branch and to each month’s. That covers clash, punishment, harm, break, six harmony, a shared harmony group, and self-punishment for 辰, 午, 酉 and 亥. Labels like Friendly, Friction and Mixed describe the relationship. They don’t say whether a month will go well for you, and they can’t stand in for a personal forecast.