Two questions that sound almost the same
“Which birthday has the fewest birth records?” and “Which date has the fewest births when it occurs?” are different questions. February 29 answers the first in this SSA dataset. December 25 answers the second among ordinary annual dates. The table gives both the frequency across all births and the average number of births per occurrence so that difference is visible.
The ordering below starts at rank #366, the fewest total records, and works toward more common dates. National rank #1 always means most common, including elsewhere on the site. There is no reversed ranking system to remember when you move between this list and the most-common birthday list.
Leap day, Christmas and New Year
February 29 appears only in 2000, 2004, 2008 and 2012 within the sample. Its 41,869 births give a frequency of about one in 1,485. That figure reflects the actual sample’s leap years and birth counts; it is not a blanket one-in-1,461 calendar rule.
December 25 appears fifteen times and has 96,568 recorded births, about one in 644 of all records. January 1, December 24 and July 4 also sit near the rare end. These fixed U.S. holidays provide descriptive landmarks. The counts do not establish the reason for an individual delivery date or show that the same pattern holds in another country.
What this ranking can and cannot tell you
The data cover births from 2000 through 2014, supplied by SSA and compiled by FiveThirtyEight. We do not project the counts onto today’s population. We also do not award a personal score for having an uncommon birthday. Every date can be meaningful, and numerical rarity is just one interesting comparison.
Find your own row in the month tables or choose it in the calculator above. The result can be saved as an image with its source years attached. Read how the denominators work before comparing an answer from another source: a different period, country or leap-day treatment can change the ranking.
Good questions
Is February 29 rarer than Christmas?
Yes, across all birth records in this sample. Leap day has 41,869 births across four occurrences; Christmas has 96,568 across fifteen. Per occurrence, Christmas has the lower daily average.