This is a model, built for fun. It turns public statistics into an educated guess. It is not a census and will not be 100% accurate: expect uncertainty of tens of percent, and more for people born before about 1950. That is why the numbers are rounded to two significant figures.
The data we pull in
- Population and birth rates by country (World Bank, i.e. UN estimates), 1960 to today. This gives the number of babies born in each country each year.
- Life expectancy and infant mortality (World Bank) for every country and year, to estimate how likely a person is to still be alive.
- Today's age structure (World Bank): how many people of each age live in each country. We use it to correct the model for older people.
- Births by month (Eurostat for Europe, Australia's ABS, the Philippines' PSA, Brazil's IBGE) to learn which times of year are busier for births.
- Daily births in the US (CDC/NCHS) to learn that fewer babies arrive on weekends and holidays such as 25 Dec and 1 Jan.
- Estimates for 1926 to 1959, where no official birth rates exist: we work backwards from 1960 and world population totals (Japan uses its recorded birth counts). These years are the shakiest.
How your number is calculated
- Births that year. For each country, births in your birth year = population × birth rate.
- Births on your day. Divide by 365.25 for an average day, then adjust for the time of year, the day of the week and whether it was a holiday.
- Still alive. A mortality curve is fitted to each country and year from its life expectancy and infant mortality, then followed through a person's life up to today. For ages 50 and over the result is nudged to match the real age structure.
- Add it up. Births on your day × chance of surviving, summed over every country, gives the count of living people with your birthday. Each country's share is where those people were born.
- The map. Colour shows the count per country, or per million residents so small countries compare fairly.
Things to keep in mind
- Locations are the country of birth. People who have moved are not tracked.
- Weekday and holiday effects are measured in the US and scaled down for countries and eras with fewer scheduled deliveries.
- The data is refreshed every three months; last updated –.
Curious about the detail? The full method, sources and known limits are written up in the project's docs folder.