How Common Is My Birthday?

By the Age-Finder team · Last updated 7 November 2026

How Common Is My Birthday? shows how popular your birthday is, using 21 years of U.S. birth records. Choose a month and day to see its rank out of 366 dates, the average number of babies born on that date and how it compares with an average day.

How to Use the Birthday Rarity Calculator

1. Choose the month and day of the birthday. The year does not matter.
2. Select Check my birthday.
3. The result shows the rank, where 1 is the most common birthday and 366 the least, the average births on that date and the difference from an average day.

For the days until your next birthday, use the Birthday Calculator.

Where the Data Comes From

The calculator uses U.S. births for every day from 1994 to 2014: the National Center for Health Statistics (part of the CDC) for 1994 to 1999 and the Social Security Administration for 2000 to 2014, published together as an open dataset by FiveThirtyEight.

For each calendar date, it averages the births across all 21 years. For 29 February, it averages only the five leap years in that period. On an average day, about 11,174 babies were born in the United States in that period.

Why does the data end in 2014? The CDC’s public natality service no longer publishes births by day of month, for confidentiality reasons, so no analyst can compute fresh calendar-date counts from the same data.

The 1994 to 2014 series, 85,386,227 births over 7,670 days, remains the most detailed public record of when Americans are born, and the relative rankings are stable across decades, so the order does not go stale.

How to read your rank

The calculator gives your birthday a label as well as a rank. Rank 1 to 37 means one of the most common birthdays. Rank 38 to 110 means a common birthday.

Rank 111 to 256 means an average birthday. Rank 257 to 330 means a less common birthday. Rank 331 to 366 means one of the rarest birthdays.

Worked example: 14 May ranks 192nd of 366, with about 11,109 births on an average 14 May, so it is an average birthday by the tool’s labels, almost exactly in the middle of the year.

September 9 sits at the opposite end: rank 1, about 12,344 births, which is 1.87 times the 6,601 births of Christmas Day.

The Most Common Birthdays

Mid-September dominates. Babies born then were typically conceived around late December, during the winter holidays.

The Rarest Birthdays

The rarest birthdays are major holidays. Today many births are scheduled by induction or caesarean section, and fewer are scheduled on holidays, so fewer babies are born on those days. Thanksgiving dates in late November show the same pattern: every date from 22 to 28 November ranks between 336 and 360.

What About 29 February?

On the days it exists, 29 February ranks 347th, with about 10,512 births. But it only exists once every four years, so in any four-year period fewer people are born on 29 February than on any other date.

That makes it the rarest birthday overall. Your chance of being born on 29 February is about 1 in 1,461, against 1 in 365 for any other date. For how ages are counted for leap-day birthdays, see our leap year birthdays guide.

Birthdays by month

September has the busiest days: 11,811 births on an average date, ahead of August at 11,712 and July at 11,563. January is the quietest, at 10,721 births per date.

August still has the most births in total, 363,078, because it has 31 days against September’s 30. The totals are for an average year; February’s includes 29 February, which only exists in leap years.

Are the 13ths unlucky?

The twelve 13ths average 10,942 births, a little below the overall average of 11,174, and their mean rank is 260th.

That looks like a superstition effect until you look at the months: the January to May 13ths all rank between 331 and 351, in the quiet half of the year, while 13 September ranks 33rd, one of the most common dates of all.

There is no 13th effect. The month does the work, not the number.

Why Birthdays Vary

Three patterns explain most of the differences: Seasons: more babies are born in late summer and early autumn in the United States. Holidays: scheduled births avoid holidays, which makes holiday birthdays rarer.

Weekdays: more births happen on weekdays than at weekends for the same reason, which averages out across years. The data is from the United States. Other countries show similar holiday effects, but their busiest months can differ.

Why other sites show slightly different numbers

Other sites that use the same FiveThirtyEight files report 12,301 births for 9 September and 6,574 for 25 December, against 12,344 and 6,601 here.

The difference is the year split: this calculator uses the National Center for Health Statistics file for 1994 to 1999 and the Social Security Administration file for 2000 to 2014, while the other sites use the NCHS file for 1994 to 2003 and the SSA file for 2004 to 2014.

The two files overlap in 2000 to 2003 and disagree slightly there, so the averages differ by a few dozen births. The ranking is identical on both splits: September 9 is first and December 25 is last.

Your Birthday in Context

Even the rarest ordinary birthday is shared by thousands of people each year in the United States. The gap between the most and least common dates is large on holidays, but most dates fall within a few percent of the average day.

The rank is a fun comparison rather than a mark of how special a birthday is. Birthday popularity also changes over time.

The share of births scheduled in advance has grown, which has made weekday and holiday effects stronger than they were in earlier decades. The figures here describe births between 1994 and 2014; patterns for older or younger generations differ.

Shared Birthdays in a Group

How likely is it that two people in a group share a birthday? Surprisingly likely: in a group of 23 people the chance is just over 50%, a result known as the birthday problem.

The real chance is slightly higher than the classic calculation suggests, because births are not spread evenly across the year, as this data shows. For the full maths, use the Birthday Paradox Calculator.

What other birthday rarity calculators offer

The three calculators below are the ones that rank highest when you search for how common your birthday is. Here is how this page compares with each of them.

Where this page still loses: the tool has no heatmap the way CalculatorOcean and InviteBird do, and no numeric rarity score the way BirthdayRarity does. What it adds is the month table, the 13ths check, the birthday paradox, and the file-split note that explains why the numbers differ between sites.

Frequently Asked Questions

Sources

• FiveThirtyEight: U.S. births dataset (the birth counts used).
• Age-Finder methodology (how dates are handled).