The U.S. fertility rate has been below replacement level for most of the past 50+ years. The U.S. population increased because:
- Young cohort was yet to have their own kids
- Life expectancy increased
- Immigration. As of today, immigration accounts for the largest portion of U.S. population increase.
Easily seen on this chart, births peaked in 1958-1961, then began a sharp decline. Today, there are fewer teen pregnancies (see the black line curve), and a change in when women give birth – to age 35+. When people start their families at 35+, they will have fewer kids (1 or 2) due to their late start. This means the low fertility rates will continue.
The enormous “bump” in 1958-1960 became the new worker cohort entering the job market about 1980 – with huge competition for jobs. This correlated with the huge increase in students seeking undergraduate and graduate degrees to “stand out from the crowd” (related factor was the Vietnam War educational deferment to the draft that resulted in many young continuing to graduate school, fundamentally changing the demographics for everyone, moving forward).