Do Twins Have the Same BaZi Chart?

Now and then a hospital announces twins born either side of midnight on New Year's Eve: two babies minutes apart, with birthdays in different years.

Take a pair born in New York at 23:59 on 31 December 2023 and 00:02 on 1 January 2024. BaZi gives them the same eight characters: 癸卯, 甲子, 甲子, 甲子. Its year doesn't turn until 立春, in February, so both belong to 癸卯. And by the sun, New York's midnight had already passed. The city sits east of its time zone's meridian, so solar midnight comes at 23:56 by the clock, and both babies were born on the same Jia Zi 甲子 day, in the same hour.

Born forty minutes apart instead, at 23:48 and 00:28, a pair would have different day pillars, Gui Hai 癸亥 and 甲子, and so different day masters: 癸, yin Water, and 甲, yang Wood.

So the answer to the title is: usually, but not always.

Usually, yes

In England and Wales, birth certificates record the time only for twins and other multiple births. For BaZi, the minutes between twins rarely matter.

A chart is a two-hour window, and most twins arrive well inside one. In a Swedish study of 527 twin pairs whose first baby was born vaginally, the median gap between the first birth and the second was 19 minutes. Sixty-eight per cent of second twins arrived within half an hour, and about one in nine more than an hour later.

Whether two births share an hour pillar depends on whether an edge falls between them. With a 19-minute gap, the chance of that is roughly 19 in 120, about one in six. For most twins, it's one chart.

Four edges that split them

When twins don't share a chart, it's because an edge fell between them. There are four kinds.

The hour. Hour pillars change every two hours, at times that depend on longitude. In Seoul they change at 32 minutes past each odd hour. Twins born there at 05:25 and 05:40 one June morning in 1990 share three pillars and differ in the fourth: 庚寅 for the first, 辛卯 for the second.

The day. In Seoul the day itself turns at 00:32 by the clock. Twins born at 00:20 and 00:45 that same night have different day pillars, 庚戌 and 辛亥, and so different day masters, 庚 and 辛: the yang and the yin of Metal. This is the edge in the New Year example, and it changes the most, because the day master is the point the whole chart is read from.

The month and the year. Months change at twelve of the solar terms, and the first of them, 立春, changes the year as well. That's why the calendar New Year splits nothing above the day: twins born either side of midnight on 31 December share a year pillar. Twins born either side of 立春 don't. This year it fell at 04:54 in Seoul. Born ten minutes before it and ten minutes after, two boys would be a 乙巳 Wood Snake and a 丙午 Fire Horse, with different month pillars too, 己丑 and 庚寅.

Their decades would run in opposite directions as well. Which way the luck pillars run depends on whether the year stem is yang or yin, and 乙 is yin while 丙 is yang. Twenty minutes apart, the same sex, and one walks forward through the calendar for life while the other walks back.

Sex. The fourth edge isn't in the calendar at all. Direction depends on birth sex as well as the year stem, so a boy and a girl born in the same hour share all eight characters and still get decades that run opposite ways. The boy and girl in the luck-pillar post, born the same February morning in 1990, could have been twins. His first luck pillar begins at two; hers at seven years and eleven months.

One chart, two children

Practitioners who read for twins have had to answer the obvious question. If the chart is the same, how do you read two people from it? The answers don't agree.

Some reverse one twin's luck pillars, reading that child as if born the opposite sex. Some read the elder twin's chart as the stronger of the two, in the strength verdict's sense. Some split the hidden stems of the hour branch, giving the elder its main stem and the younger its middle one. One Korean practitioner gives the elder the chart's stems and the younger its branches, and says plainly that no text or theory stands behind it. A 2021 Korean study compared four such methods and favoured one built on the hour pillar.

The chart can't settle the argument, because the chart is the one thing the twins have in common.

What twins show

Twin research has its own way of asking what makes people alike. Identical twins share virtually all their genes; fraternal twins share about half, like any other siblings. Both kinds share a birth date and, nearly always, a chart.

If the chart shaped who they became, fraternal twins would be as alike as identical ones. They aren't. Identical twins are consistently the more alike, and that difference is how twin studies measure the pull of genes. A 2015 analysis that pooled fifty years of them, 2,748 papers covering 17,804 traits, put the average share of variation down to genes at 49 per cent.

The other half of the experiment is the time-twins study: unrelated people born minutes apart, with the same chart and different parents, who turned out no more alike than anyone else. Put the two together and the shared chart drops out both times. Whatever makes twins alike, it isn't the eight characters.

Where this site stands

A reading here is built from the chart. For twins who share one, the readings are argued from the same eight characters and differ only where the chart does: the luck pillars, if the twins are a boy and a girl. Beyond that, the difference is wording.

If an edge fell between your twins, they have two charts, and the way to know is the birth times themselves. The birth-time post covers where to find them.

Twins are the closest BaZi comes to a controlled experiment: two people, one chart. Whatever makes them two isn't in it.