Birthday rankings
The birthday calculator uses 62,187,024 births over 5,479 calendar days, covering 2000–2014 inclusive. The underlying daily counts come from the U.S. Social Security Administration, as released in FiveThirtyEight’s births dataset. We use its SSA file alone. We do not combine it with the separate CDC 1994–2003 file, because the years overlap and the sources need not count exactly the same population.
For each month-and-day pair, we add every recorded birth on that date. A date’s “1 in N” value is 62,187,024 divided by its total recorded births. It describes the share of birth records in this historical sample. It does not estimate today’s living population or the probability of a future delivery on a specific date.
Rank #1 is the most common date. A rank equals one plus the number of dates with strictly more births, so any exact ties would share a rank. “Rarer than X% of other dates” counts dates with more births, divides by 365 other possible dates and multiplies by 100. This is a comparison of calendar dates, not a percentile of people. Figures are rounded for display; calculations retain their original precision.
February 29 and average births
Leap day occurs in 2000, 2004, 2008 and 2012 in this sample. Other month-and-day pairs occur fifteen times. The headline frequency keeps that difference: a randomly selected birth record is less likely to fall on a date that exists only four times. February 29 therefore has the fewest total records and rank #366.
The “births per occurrence” column answers a different question. It divides a date’s total by the number of times that date actually occurred: four for February 29, fifteen otherwise. February 29 averages 10,467 births per occurrence, which is not exceptionally low compared with some annual holidays. This conditional daily average must not be confused with its frequency across all birth records.
We do not silently replace leap day with February 28 or March 1, or assume every birthday has a 1-in-365 probability. The February table and rarest-birthday list make both measures available. The original file ends in 2014, so its ranking is not a claim about births in 2026.
First names
The first-name lookup uses the SSA national baby-name data, with birth years 1880–2024. The current site pins an older release; it does not claim to include the latest 2025 release. After the official download returned an access error during this build, we retrieved unmodified annual SSA files from a public mirror pinned to one revision. We imported only the original data files, then calculated our own counts and rankings. Source hashes and retrieval details accompany the build.
For a selected year, female and male published counts are combined for each spelling. The denominator is the sum of those published counts, not the number of all births. SSA suppresses low-frequency entries within each sex category and year. The withheld records cannot be reconstructed here, so a “1 in” result describes released name records only. A missing spelling returns no estimate, rather than a zero or an invented one-person count.
SSA explains that early records are incomplete and that the data arise from Social Security card applications; see its background notes. These are birth-year cohorts, not a census of people alive today. Rank is one plus the number of combined spellings with higher published counts. Punctuation and spaces are removed for matching; alternative spellings remain separate. The result does not infer a person’s sex, ancestry or identity.
Surnames
The surname table comes from Frequently Occurring Surnames from the 2010 Census. It publishes 162,253 surnames with at least 100 recorded occurrences. We retain the spelling, count and official rank; demographic percentage columns are not used by this product.
We divide 294,979,229 recorded surname entries by the surname’s count. That denominator includes the source’s “all other names” aggregate of 29,312,001, covering names below the publication threshold. It does not include people without usable surname records. The Census’s technical documentation, table 1 explains the coverage and editing rules. An absent name has unknown frequency in our lookup. The tool does not estimate current counts, family relationships or a name’s country of origin.
Cards, licensing and corrections
Cards preserve the population and year for each result. A combined card contains separate facts, with no multiplication of probabilities. First names, surnames and birthdays may be associated with one another, and these files do not describe the same population. Treating them as independent would manufacture a precision the data do not support.
FiveThirtyEight’s compiled data are supplied under Creative Commons Attribution 4.0. We aggregate and rank the counts, attribute the compilation on birthday results, and link this methodology on every image. SSA and Census data are U.S. government statistical releases. No agency endorses this site. The charts and card artwork are our own.
Found a calculation or source problem? Contact us with the page, dataset year and steps needed to reproduce it. Please do not send someone else’s personal information. A correction should change the calculation and every affected display together, rather than leaving old cards or tables inconsistent with the source.