How the rankings are built.
The data
Rankings show average daily U.S. births per calendar day, computed from CDC WONDER and Social Security Administration natality records covering 21 years (1994–2014) — roughly 86 million recorded births in total.
How we calculate averages
For each of the 366 calendar days, we summed births on that date across every year in the dataset and divided by the number of years that date occurred, giving an average daily figure. February 29 is included, counted only across its five occurrences in the 21-year window — which is exactly why it lands at the bottom of the rankings even though its underlying daily average looks ordinary.
Ranking
Every day is ranked 1st through 366th by its average, from busiest (12,344 births/day) to rarest (6,601 births/day). The overall mean across all days sits around 11,174 births/day.
Colour scale
Because most days cluster in a fairly narrow value range, we colour every chart by rank percentile rather than raw value — this spreads the full colour gradient evenly across all 366 days instead of compressing most of them into a single shade.
Zodiac signs
Sign popularity is the average daily birth count across all days that fall within each sign's traditional date range, using the standard Western tropical zodiac boundaries.
Conception estimates
Estimated conception dates use a typical 40-week (280-day) full-term pregnancy counted backward from the birth date. This is a statistical approximation, not a medical calculation — actual gestation length varies.
Limitations
This data reflects U.S. births only and doesn't account for regional, cultural, or more recent trends beyond 2014. It's built for curiosity, not medical, legal, or astrological advice.