Baby Math

I was listening to a news program this weekend when I heard a journalist say that "4 million babies are born in the US every year." When I heard that statistic, I thought that I should be able to estimate that number using generally available information. Another Fermi problem!

But before we begin, I was inspired to write this post after speaking to two of my best friends. They have just had a baby and I got to meet her for the very first time a few days ago. She might only be a few months old, but already her parents have started playing educational songs and YouTube videos to keep her entertained! They are big believers in the notion that babies learn through music and I have to admit, some of the songs were pretty catchy so I can definitely see the appeal.

Now, baby news to one side, let's see if we can come up with a rough estimate of the number of babies born in the US every year. Here is my line of reasoning.

  • There are about 310 million people living in the US. For rough figuring, let's say 320 million because it has more even divisors.
  • Half the US population are women, which means there are 160 million women in the US.
  • Assume that US women have a life expectancy of 80 years, with 20 years being the primary childbearing years. So at any time, 25% (40 million) of US women are in their childbearing years .
  • Most of these women will experience a healthy birth and will bring an equally as healthy newborn into the world. There will be others, however, who won't have the same joy in that their child could be born with a birth defect - visit somewhere like LawTX to learn more about what they are and how you can proceed with your compensation claim.
  • The average US family has around 2 children. So US women spend roughly 2 years of their 20 childbearing years pregnant (10% of their childbearing years).
  • So at any one time about 4 million women are pregnant in the US.
  • Since most of these women have one baby at a time and pregnancy takes roughly a year, I would expect that 4 million babies are born in the US each year.

I was able to estimate that 4 million babies are born in the US each year using generally available information. This agrees nicely with the actual value of 4,055,000 (2010). Whenever I hear a statistic, I always like to think about it and see if it makes sense. Hearing that 4 million babies are born in the US each year now makes sense to me.

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  1. Pingback: How many people have been born over time? | Math Encounters Blog

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