What BirthdayLab is
BirthdayLab is a focused data-and-tools site about everything encoded in a date of birth — how rare it is, the day of the week it fell on, the month and the generation it belongs to, whether it's a leap day, how many people share it, and the demographics behind when people are born. The audience is anyone curious about the data behind their own birthday or someone else's.
The site is small by design. A tight cluster of substantial, interactive pages — each built from primary data — does the work that thousands of thin per-date pages cannot. Every tool computes its answer in your browser; no inputs are sent to or stored on our application servers.
Who runs it
BirthdayLab is operated by Moving Data Systems, d.o.o., a company registered in Slovenia, EU. Moving Data Systems, d.o.o. is an independent operator of data-driven reference sites. The Organization metadata on every page links back to this page as the human-readable counterpart of the sitewide schema.
Day-to-day editorial and engineering work — the dossiers, the prose, the SVG visualisations, the build-time sanity gates — is done by a small team. We don't outsource writing or republish other sites' tables; we don't run a content farm.
How BirthdayLab is built — the sourcing standard
This is the most important section on the page, because it describes the line that separates BirthdayLab from auto-generated or spun content. Everything on the site is built from primary, authoritative sources that we name in plain text on each page.
The primary sources we draw on:
- U.S. CDC / NCHS National Vital Statistics System — final U.S. births by year, the natality data brief series (Data Brief 535 for the 2024 final), and the Natality Trends data-visualisation series for the 1909–present arc. Used on the Birth Statistics hub, the Birth-Rate Trends page, and the per-day figure on Birthday Twins.
- U.S. Social Security Administration — Period Life Table, 2023 (2026 Trustees Report) — life expectancy by age, used on the Age Calculator.
- United Nations World Population Prospects, 2024 Revision — global births and population. Used on Birth Statistics, Birth-Rate Trends, and Birthday Twins.
- U.S. Census Bureau — population estimates used on Birthday Twins.
- FiveThirtyEight U.S. births by date dataset — 1994–2014 daily birth records (CDC/NCHS 1994–2003 + SSA 2004–2014), used under the Creative Commons Attribution 4.0 licence. Underlies the Birthday Rarity Calculator, Day of the Week Born, Birth Month, and the date-frequency scaling on Birthday Twins.
- U.S. Naval Observatory + NIST — for the Gregorian leap-year rule and the length of the tropical year. Used on the Leap Year Calculator.
- Pew Research Center + McCrindle Research — for the generation birth-year ranges. Pew is credited for Silent through Gen Z; McCrindle for Gen Alpha and Gen Beta. The Generation Calculator names each attribution explicitly.
Figures are computed, not copied. The rarity dataset is reduced from 85.4 million daily birth records by code in the repository, not from a third-party summary table. A build-time sanity gate cross-checks every page's anchor figures against the dossier — if a number drifts beyond tolerance, the build refuses to ship.
Verified-or-omitted. If a number can't be traced to a primary source, it doesn't go on the site. Estimates (like the worldwide birthday-twin count on Birthday Twins) are labelled as estimates and prefixed with a tilde so a reader can never mistake an approximation for an exact figure.
Original tools and visualisations. Every calculator, every SVG chart, every count-up animation, every live ticker on the site was built specifically for BirthdayLab. We use no embedded third-party calculators, no charting libraries, and no spun text. The interactive experience is part of the substance, not decoration.
What you'll find on the site
A short tour of the main tools — each links to the methodology for its own page:
- Birthday Rarity Calculator — rank any date among the 365 + Feb 29.
- Age Calculator — exact age in years/months/days plus a life-expectancy module from the SSA period life table.
- Birthday Paradox — the 23-for-50.7% result, a real-distribution simulator, and the cryptographic twist.
- Birth Statistics hub — U.S. and world births by day / hour / minute / second.
- Birth-Rate Trends — the 1909–present U.S. arc, downloadable CSV.
- Day of the Week Born — Tuesday is the busiest U.S. birth day; weekends are quietest.
- Birth Month — the per-day vs total split (September leads per day, August by total).
- Leap Year — live countdown to Feb 29, 2028, plus the century-rule math.
- Generation Calculator — Pew through Gen Z; McCrindle for Alpha and Beta, with the 2010–2012 overlap shown.
- Birthday Countdown — live ticker to your next birthday.
- Birthday Twins — how many people share a date, scaled by the date's actual U.S. birth frequency.
Accuracy and corrections
We aim to be wrong as rarely as possible and to fix it quickly when we are. If you find a figure that doesn't match its cited source, write to hello@birthdaylab.net with the page URL and the specific number. Verified corrections are applied promptly; the page's last-reviewed date is bumped in the same commit.
Contact
The contact address is hello@birthdaylab.net or via the contact page. For data-handling and privacy questions, see the privacy page.
Last reviewed .