The “half your age plus seven” rule — how often is it broken?

Andrey Kamenov

Andrey Kamenov, Ph.D. Probability and Statistics

When is an age difference between partners a little too large? A common rule is that you cannot date someone younger than half your age plus seven. For example, if you are 30, dating someone 22 years old is just barely acceptable.

The following chart illustrates this concept: couples between the dashed lines are the ones following the rule.

Distribution of partners’ ages in unmarried couples

Distributon of partners' ages in unmarried couples

The rule itself, according to Wikipedia, has French origins — but how often is it broken in the U.S.?

Census data on married couples won’t help us much. The (relative) age disparity lessens as both partners grow older. Let’s instead focus on couples who are living together but are not married yet.

It appears that breaking the rule is getting less and less common. Only 3.6 percent of all couples fall outside the “acceptable” range — compare this to 6.7 percent 10 years ago. Only around a quarter of them are hypergamous, where the woman is older.

Unmarried couples with significant age disparities, 2007-2017

Another interesting fact is that significant age disparities are much less common in Asian couples. The percentage here (2.7 percent of all couples) is at only half of the national average. None of the other races exhibited any statistically significant differences.

And of course, it’s interesting to see the difference between states. Here’s the map:

Unmarried couples with significant age disparities by state

Suffice to say, the difference is pretty significant. While numbers around 3 percent are registered in Iowa and Vermont, rates in excess of 8 percent can be seen on the map. Examples of such states include Oklahoma and Arkansas.


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About Andrey Kamenov

Andrey Kamenov

Andrey Kamenov, Ph.D. Probability and Statistics

Andrey Kamenov is a data scientist working for Advameg Inc. His background includes teaching statistics, stochastic processes and financial mathematics in Moscow State University and working for a hedge fund. His academic interests range from statistical data analysis to optimal stopping theory. Andrey also enjoys his hobbies of photography, reading and powerlifting.

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