How Many People Share My Birthday?

How many share my birthday worldwide and in the U.S.?

A useful starting point: divide world population by the number of days in a year. With world population around ~8.2B (U.N. World Population Prospects 2024 Revision, rising by roughly 75 million per year) and 365.25 days, you get about ~22.5M people on an average calendar date.

The U.S. arithmetic is the same. With about ~340.1M people per recent U.S. Census Bureau estimates, an average date has roughly ~931k birthday twins in the United States — close to a million.

That flat "population divided by 365" is the back-of-an- envelope number. It's a fine ballpark but it isn't the best answer this page can give, because birthdays aren't evenly distributed across the year — and the rest of this page uses real U.S. birth records to adjust it.

For international scale: per the United Nations, World Population Prospects 2024 Revision, India and China each hold nearly ~1.4B people. Each one alone has roughly ~3.83M people on an average calendar date — roughly four times the U.S. count for the same date. The U.S. at ~340.1M holds about 4% of an average date's worldwide twins. UN states India and China at roughly 1.4 billion each at its published precision; the page never prints precision beyond what UN states directly.

Does it depend on my date?

Yes — meaningfully. U.S. births cluster in late summer and fall away on holidays and weekends. Across the 1994–2014 series of 85 million U.S. births, an average September day recorded about 11,800 births while December 25 recorded only about 6,600. The same pattern persists across the decades; it isn't a one-off.

So a better estimate scales the headline number by your date's actual relative frequency. A September 9 birthday comes in around ~24.8M worldwide — about 10% above an average date. A December 25 birthday sits near ~13.3M, around 40% below.

The tool above uses that adjustment automatically: the frequency multiplier comes from the same dataset that powers the Birthday Rarity Calculator. The chart below shows the spread between the peak, an average date, and the lowest non-leap date.

Where in the U.S. — your birthday twins by state

The roughly 931,173 average-date U.S. count splits across the 50 states and DC by population. California holds the largest single share at about 107,957 birthday twins on the average date; Wyoming, the smallest by population, holds about 1,609. The top five states by population (California, Texas, Florida, New York, Pennsylvania) hold about 37% of the national count between them.

Source: U.S. Census Bureau, Vintage 2024 population estimates (POPESTIMATE2024, July 1, 2024). The full table below shows all 51 jurisdictions with their population and the average-date count. Multiply any row by your date's frequency multiplier from the tool above to personalize — September dates run about 10% above average, December 25 about 40% below.

How many were born on my exact day?

The "birthday twins" estimate counts everyone alive who shares your month and day. A tighter version counts only people born on your exact calendar date — same month, same day, same year. Those are your same-age birth-day twins.

In the United States that's roughly 9,900 per day (3,628,934 births in 2024 ÷ 366 days, CDC/NCHS final). Worldwide it's roughly 370,000 per day (about 134 million annual births per the U.N.). The two figures sit on the Birth Statistics hub alongside the per-hour, per-minute, and per-second breakdowns.

These are exact-day figures for the current year — they don't scale linearly with age. The 9,900-a-day for someone born in 2024 will be different from the figure that applied to someone born in 1985, when the U.S. recorded about 3.76 million births in a year.

How many of them are still alive today?

Some of your birthday twins were born in the same year you were. The 2023 SSA period life table tracks 100,000 newborns of each sex through every age — applied to a birth year, it gives a population-average estimate of the original cohort that remains alive today. This is a demographic average for the U.S. Social Security area, not a personal prediction.

The estimate uses a period basis, meaning it assumes today's mortality rates held throughout the cohort's lifespan. For older birth years that actually lived through declining U.S. mortality (the 1950s through the 2000s saw steady gains in life expectancy), the true survival is somewhat higher than this period estimate suggests. The period figure is a conservative approximation; the cohort reality is more favourable.

The full survivor curve, with separate male and female lines, the sex-gap visualization, and milestone tables, lives on the Age Calculator. That page uses the same SSA 2023 source data this section reads from — no duplication, just different angles on the same vendored table.

Leap-day twins

If you were born on February 29, the calendar takes care of the rest: leaplings number only about ~5M worldwide — roughly a quarter of a typical date's count. The reason is calendar arithmetic, not biology. February 29 occurs once every four years, so the population accumulating on that date is correspondingly smaller.

We don't derive the leapling figure from the same date-frequency multiplier used for other dates because the multiplier would understate the effect. The 1-in-1,461 calendar-occurrence rate dominates; the natural- distribution effect is a secondary correction. The Leap Year Calculator carries the full math and a live countdown to the next Feb 29.

Will I ever meet one?

Probably more often than feels rare. There are roughly ~931k people in the U.S. with your birthday on an average date — enough that you almost certainly know a few without realising. The standard mathematical question, though, is how many people you need to guarantee a match: a 50% chance that someone in the room shares your birthday needs about 253 people.

That seems high until you compare it to the famous birthday paradox: in a room of just 23 people, there's already a 50.7% chance that some two people share any birthday — not yours specifically, but at least one match among everyone in the room. The 253-vs-23 gap is the same math under two different questions.

The full curve, the simulator, and the cryptographic twist live on the Birthday Paradox page.