Top-name share
Top 10 shows the names everyone heard constantly. Top 50 shows the broader common-name shelf losing power.
06 / Individuality
The Naming Diversity Index
In 1880, ten boy names captured 44% of recorded boy births. Ten girl names captured 25%. By 2025, both pools had fallen below 8%. The quiet revolution was not just a decline in John and Mary. It was the birth of a much longer tail.
Boys, top-ten share
Girls, top-ten share
Effective boy names
118 -> 1,382
Effective girl names
193 -> 2,119
The same hundred births, four ways
Each panel is 100 births in that sex and year. Dark squares are the top ten names; lighter squares are ranks 11 through 50. The white space is the rest of the naming universe.
Concentration collapses, but not from the same starting point
Boys began with a much tighter canon. Girls were already more varied in 1880, then moved into an even wider naming field as the top 50 lost its hold.
Entropy and effective names
Higher entropy means the next baby's name is harder to predict. Effective names translates that entropy into a more intuitive count.
-36.2 pts
Boys had the sharper collapse in top-ten concentration.
1.5x
Girls still have the larger effective name pool in 2025.
31,227
Distinct name/sex observations appear in the 2025 national files.
Data: U.S. Social Security Administration national baby-name files, 1880-2025, from the checked-in Name Vitals ingest migrations. Top-ten and top-fifty shares are calculated within sex: ranked name counts divided by recorded births for that sex and year. Shannon entropy is calculated across all recorded name counts for a sex/year. Effective names are 2^entropy. SSA suppresses names with fewer than five births in a given year, so the deepest tail remains unobserved.