How Many People in the World Share Your Zi Wei Dou Shu Birth Chart?

After casting a birth chart, many people’s first thought is, “This chart is mine.” But look at it another way: the combinations of birth year, month, day, double-hour and gender are finite. How many different charts are there in the world, and how many people share the exact same one as you?

No need to guess. We simply let Xingge’s chart-generation engine run through every possible combination.

How we calculated it

The count of chart types below follows the Chinese lunar calendar settings used by the original chart-generation engine. The population examples have been updated to official 2025 figures for this language market (verified on October 31, 2026).

Zi Wei Dou Shu (Purple Star Astrology) chart generation looks at only five factors: the Heavenly Stem and Earthly Branch year, the lunar month, the lunar day, the Chinese double-hour, and gender. It does not care which Gregorian year you were born in, only whether that year was Jia Zi or Yi Chou. Thus, there are only 60 possible years, cycling every 60 years.

We ran through all combinations of 60 sexagenary cycle years × 12 months × a maximum of 30 days per month × 12 double-hours × 2 genders, subtracting the few year-month combinations that never have a 30th day, resulting in a total of 518,000 sets of birth data. Each set was processed using the same chart-casting program used by the App, following the same rules: the late Zi hour (11:00 PM to 12:00 AM) is counted as the next day; the year boundary is defined by the first day of the first lunar month; for leap months, the first 15 days are counted as part of the current month, and from the 16th day onward they are counted as part of the next month, so no separate chart casting is required.

Then we compared the generated charts one by one. Only if the Major Stars, Auxiliary Stars, Minor Stars, Four Transformations (Si Hua), brightness levels, Decade Luck (Da Xian), and Five Elements Bureau were all identical did we count them as the same chart.

The answer: about 456,000 charts

• Full unique charts: 455,908 types, approximately 456,000.
• Ignoring gender: Exactly half, 227,954 types. Men and women receive the exact same stars; the difference lies only in the direction Decade Luck flows and the arrangement order of minor star groups like Chang Sheng and Bo Shi.
• Looking only at the arrangement of the 14 Major Stars: There are only 144 types. Zi Wei has 12 possible positions, and the Life Palace has 12 possible positions. 12 × 12 covers all possibilities.

The number 144 is small. According to official US statistics for 2025, there were 3,612,012 newborns. If we distribute them evenly across the 144 Major Star configurations, each configuration would have about 25,000 people. So it is not surprising at all to meet someone at school or work who has the exact same Major Star configuration as you.

In the same year, how many people share your chart?

The Stem-Branch year cycles every 60 years. Therefore, within any given Stem-Branch year, the number of different charts is approximately:

455,908 ÷ 60 ≈ 7,600 charts

Next, we divide by actual birth numbers. The United Nations World Population Prospects 2024 estimates about 132 million newborns globally each year. According to US CDC/NCHS 2025 Birth Statistics (Final Numbers), there were 3,612,012 births in the US in 2025. These are final numbers released in October 2026. Note that we are using annual birth counts to estimate magnitude here, not counting actual individual charts.

• Worldwide: 132 million ÷ 7,600 ≈ 17,000 people
• United States: 3,612,012 ÷ 7,600 ≈ 475 people

In other words, the number of people born in the same year as you with the exact same chart is roughly the size of a small town worldwide, and about 475 people in the US under an even-distribution model. If we include people born 60 or 120 years earlier in the same Stem-Branch year, the number grows even larger: it is entirely possible that you share the exact same chart with an elder 60 years your senior, provided they were born in the same lunar month, day, and double-hour.

The 1st and the 13th can produce the same chart

During the calculation, we made an unexpected discovery: the 518,000 birth time sets produced only 456,000 unique charts, a difference of 62,000, or about 12%. This means some different birthdays result in the exact same chart.

For example, a person born at the Zi hour on the 1st day of the first lunar month in 1990, and a person of the same gender born at the Zi hour on the 13th day of the same month, will have identical charts.

Here is why: On the entire chart, only two types of stars consider the birth "day." One type includes San Tai, Ba Zuo, En Guang, and Tian Gui. These stars are counted starting from the positions of Zuo Fu, You Bi, Wen Chang, and Wen Qu. Since the chart has only 12 boxes, the count returns to the same box every 12 days. The 1st and the 13th differ by exactly 12 days, so these four stars land in their original positions again.

The other type is Zi Wei. It is calculated based on the lunar day and the Five Elements Bureau. Usually, the 1st and the 13th would fall into different boxes. However, for certain Five Elements Bureau types (in this example, Earth 5 Bureau), the calculation lands both days in the same box. When Zi Wei is in the same position, the other thirteen Major Stars follow suit. The remaining stars do not depend on the day at all, so the entire chart overlaps.

These numbers come with caveats

• Births are not evenly distributed: More people are born in certain months or at certain times, making some charts more common than others. The calculations above represent an average under an even-distribution model, not the actual measured count for any specific chart, nor an individual’s precise probability.
• Double-hours depend on local time: The Zi hour in New York and London differs by several hours. The 17,000 people worldwide were each born during that double-hour in their own respective time zones.
• Stem-Branch years are not Gregorian years: The year changes on the first day of the first lunar month, not January 1. Births before Lunar New Year belong to the previous Stem-Branch year; dates in January and February need to be checked individually.

Same chart, different lives?

There is a common folk tale: After Zhu Yuanzhang became emperor, he found a man born in the same year, month, day, and double-hour as himself, yet the man was merely an elderly beekeeper. This is a legend about Ba Zi (Four Pillars of Destiny) with no reliable source, but it raises a genuine question: Why do lives differ when the chart is the same?

The answer lies in the numbers above. In the average model, the roughly 475 people in the US who share your chart in the same year were born into different families, met different people, and made different choices. A birth chart describes tendencies, such as where you habitually focus your energy or what tends to cause obstacles for you. It is not a script.

This is also how Xingge speaks. For the same chart, Xingge provides the same interpretation to everyone who receives it. Therefore, it can only discuss tendencies, not pass judgment on your fate. The chart is the map you receive at the start of your journey, but how you walk the path is up to you.