A friend of mine recently became pregnant. One of the more woo things she has come out with is Chinese Birth Charts.

On the admittedly tiny data set of 5 the chart was 100% accurate.

Chinese Birth Charts

The Chinese Gender Table

It is said that sometime during the 13th century, a Chinese scientist developed a special calendar to predict the gender of an unborn child based on the mother's age and month of conception. Chinese women have always respected and valued this calendar, but now more recent studies in the United States are showing a success rate of over 90 percent. Enjoy the Chinese gender calendar, but keep in mind that it is for entertainment purposes only.

How to use this table

The only thing you have to do is look up your month of conception and the age you were at that moment. The intersection of the two lines indicates a B for a boy or a G for a girl.

We can not be held legally responsible for the accuracy of this ancient calendar, but it's fun to try!

I in no way believe this can be 90% accurate as some claims make out, but I'd like to see some studies.

Can any one please point me to studies/papers that prove one way or another?

  • It's not accurate for my son... I doubt though that anyone would waste time to study (or accept a paper) on this kind of stuff.
    – Sklivvz
    Commented Feb 28, 2011 at 20:29
  • 1
    It's 75% accurate for me, but I would suggest that that is in line with standard deviation with such a small sample (4 in this case)
    – Ardesco
    Commented Apr 20, 2011 at 13:50
  • Astrology (or, to be pedantic, belief in astrology) affected births in nearby Japan markedly in 1966: en.wikipedia.org/wiki/Demography_of_Japan
    – Golden Cuy
    Commented Dec 29, 2018 at 7:51
  • 5
    I find it funny that an (unnamed) Chinese scholar from the 13th century bothered about women given brith at age 40-45 but not at age 13-17... Also, should we read the chart using the age of the mum during conception or when giving birth ?
    – Evargalo
    Commented Jan 2, 2019 at 14:03

2 Answers 2


I found this website and several others with very similar text which describes the hypothesis.

It talks about male and female sperm carrying opposite electrical charges, and the female ovum cycling between positive and negative charges thus determining which sperm can fertilize it. Apparently this cycle is synchronized for all women everywhere and thus can be conveniently charted.

The page also talks about some research that confirmed this hypothesis, including one that said that sperm were either attracted to cathodes or anodes depending on whether they carried an X or Y chromosome. I found this bit on sperm sorting which describes labeling the sperm with a dye that attaches to DNA (and X chromosome has more DNA so will fluoresce more brightly), and then attaching a charge to each one using a single droplet of charged fluid, before sorting them. I suspect this method was confused as the sperm already carrying a charge.

The only thing that differs between male and female sperm is the DNA they are carrying. They do not only carry an X or Y chromosome, they carry fully half of the entire human genome, including one of the sex hormones. If the X and Y chromosomes have opposite charges, what charge do the rest of the chromosomes have? What happens when an X and Y chromosome are combined in a cell nucleus--do they tear through the rest of the genetic soup to snap together like fridge magnets? DNA is all made of the same stuff and the charge carried by each chromosome is the same (that is, none), so this theory can't possibly be true.

The real odds of this chart are 50%, the same as all the other outside-the-genetic-laboratory sex selection techniques.

  • 7
    "real odds of this chart are 50%, the same as all the other outside-the-genetic-laboratory sex selection techniques" - citation required. (Because it isn't true, because babies aren't 50% male.)
    – Oddthinking
    Commented Dec 29, 2018 at 9:35
  • 2
    @oddthinking it’s accurate if you’re rounding to the nearest ten percent, ie only one significant figure.
    – Golden Cuy
    Commented Dec 29, 2018 at 19:54
  • The sperm sorting technique you said confirmed the hypothesis did nothing of the sort. The technique described is not based on any "inherent" charge of male or female sperm but purely on the different size (x and Y chromosomes are very different in size). There is no easy biological way to switch the preference from male to female.
    – matt_black
    Commented Dec 29, 2018 at 21:37
  • 4
    @Oddthinking It does not matter that babies aren't 50% male. A chart predicting 50% males will be right 50% of the time whatever the actual frequency. Consider the case of 100% males, or any frequency.
    – User65535
    Commented Sep 8, 2022 at 10:08
  • @User65535: Oooooh! Yes
    – Oddthinking
    Commented Sep 8, 2022 at 10:18

It's easy to see that the predictions don't make any sense:

  1. The ratio of boys to girls born is well known: 105 boys versus 100 girls.

    In other words we should see 172 "B" and 164 "G". Instead we see 162 "G" and 174 "B" and hence a ratio of 107 boys versus 100 girls.

    Surely, then this calendar can't account for the measured data.

    Note: this points assumes an overall uniform birth rate over the age of mothers and months of conception. As such it is as correct as this assumption.

  2. The ratio of sexes at birth is almost independent of the age of the mother. The calendar predicts something like this graph: enter image description here

    As you can see it is completely inconsistent...

  3. If there was any truth to the calendar, then why would a different source show a completely different calendar?

As a (amusing?) side note. If one was to always predict a boy, they would be right 51% of times! More than random chance :-)

  • 4
    Regarding #1, you're assuming an even distribution of conception dates. Likely a logical assumption if your data set is as large as the population of the world, but who knows, maybe certain days of the week have higher conception rates? Commented Feb 28, 2011 at 22:55
  • @Keith: correct. I should specify that.
    – Sklivvz
    Commented Feb 28, 2011 at 22:57
  • I do not know whether the diamond moderator Sklivvz would approve of an answer being based on logic :) skeptics.meta.stackexchange.com/questions/1019/…
    – Golden Cuy
    Commented Dec 29, 2018 at 7:42
  • The answer is based on facts: the ratio of boys to girls needs to be the same as the real one; it needs to be almost independent of the age of the mother; predictions need to be consistent. Point 1 and 2 are based on the wikipedia link, point 3 has its own source.
    – Sklivvz
    Commented Dec 29, 2018 at 16:52

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