THE UK
105.3 to 100
Official UK analysis of 3.4 million births from 2019 to 2023 found 105.3 boys born for every 100 girls.
Pick a year
WHAT THE NUMBERS SHOW
A few more boys,
every year.
Slightly more sons are born than daughters.
In the UK from 2019 to 2023 there were about 105 baby boys for every 100 baby girls. The pattern is old, steady and found around the world, and counting it helped give birth to modern statistics.
105 : 100 boys to girls
Pick a year- About 105 boys per 100 girls
- Steady for a century
- First tested in 1710
- A small tilt, counted for centuries
THE SHORT ANSWER
About 105 boys
for every 100 girls.
The ratio barely moves from year to year.
Large numbers of births make the pattern clear.
THE WORLD
A narrow natural range
In most countries the normal sex ratio at birth is between 102 and 106 males per 100 females; worldwide it is estimated at about 1.05.
See the numbers
THE HISTORY
Counted since 1710
John Arbuthnot found that in every one of 82 years of London records, more boys were born than girls, an early test of statistical significance.
Read the historyGeneral information only, not professional safety advice. If someone is in immediate danger, call the emergency services.
FOUR WAYS TO READ A SEX RATIO
Small differences,
big numbers.
A sex ratio is a simple sum, but it is easy to misread. These points come from the official methodology and reference works.
Know the formula
The ratio is male births divided by female births, times 100: the number of boys born per 100 girls.
Use large numbers
In a single family or small town, chance swamps the pattern. It only shows clearly across many thousands of births.
Expect a narrow range
Most countries sit between 102 and 106 boys per 100 girls. Figures well outside that range are unusual and are studied closely.
Watch for other factors
Studies link small shifts to things like parents' ages and the sex of previous children, though findings vary between studies.
TWO NUMBERS WORTH KNOWING
Steady in the UK,
similar worldwide.
One figure on how stable the UK ratio is,
one on how long it has been counted.
106.7 per 100
Highest UK sex ratio at birth, 1910 to 2023
The UK ratio has never gone above 107 since 1910. It ranged from 103.5 in 1914 to 106.7 in 1973.
UK RANGE · DHSC
82 years
Consecutive years of more boys in London records
From 1629 to 1710, every year's London records showed more male births than female. Arbuthnot reckoned the odds of that by chance at 1 in 2 to the power 82.
HISTORY · ARBUTHNOT, 1710
Laplace later used the statistics of almost half a million births, which also showed an excess of boys, in developing probability theory.
PICK A YEAR
How many boys
per 100 girls?
Choose a period to see the UK's sex ratio at birth. The bar shows whether it sits at the low, middle or high end of the UK's range since 1910.
Based on the Department of Health and Social Care's official statistics, Sex ratios at birth in the UK: 2019 to 2023.
THE FIRST SIGNIFICANCE TEST
Eighty-two years,
counted.
In 1710 the physician John Arbuthnot published a paper in the Royal Society's Philosophical Transactions on 'the constant regularity observed in the births of both sexes'. He used London birth records for each year from 1629 to 1710.
Boys outnumbered girls every year. If each birth were an even chance, that run would be fantastically unlikely, so he concluded it was not chance. In modern terms he had carried out a sign test and calculated a p-value, now seen as one of the first uses of a significance test.
Questions
Questions people ask
Are more boys than girls born?
Yes, slightly. In the UK from 2019 to 2023 there were 105.3 boys born for every 100 girls, and most countries fall between 102 and 106.
Has the UK ratio changed over time?
Only a little. Since 1910 it has ranged from 103.5 in 1914 to 106.7 in 1973, and since 1980 it has stayed between 104.7 and 105.8.
Does birth order matter?
Across all UK births from 2019 to 2023, the ratio did not vary significantly by birth order, staying between 105.2 and 106.8 boys per 100 girls.
Who first noticed the pattern?
Early statisticians studied it. John Arbuthnot's 1710 paper on 82 years of London births is credited as one of the first uses of a significance test; Laplace later analysed almost half a million births.
Why is the ratio roughly even at all?
Ronald Fisher argued in his 1930 book, in terms of what parents invest in offspring, that a roughly 1:1 ratio is the evolutionarily stable strategy. Many other species do depart from it.
Sources
- GOV.UK (DHSC): Sex ratios at birth in the UK, 2019 to 2023
- GOV.UK (DHSC): Sex ratios at birth in the UK, 2019 to 2023, technical appendices
- ONS: Births in England and Wales, summary tables 2023
- Wikipedia: Human sex ratio
- Wikipedia: John Arbuthnot
- Our World in Data: Gender ratio
Updated