How Rare Is My Birthday?

About the How Rare Is My Birthday?

Not all birthdays are equally likely. In the United States, more babies arrive in mid-September than almost any other time of year, while Christmas Day and New Year's Day sit near the bottom. This calculator ranks every day of the year from most common (1) to rarest (366) using real birth counts, then shows how your own date compares.

It also tells you roughly how many people share your birthday, how far above or below an average day it sits, and the chance that someone in a group of a given size was born on the same day as you.

The data comes from US births between 2000 and 2014, so the ranking reflects the United States. Other countries have different patterns, so treat it as a fun guide for birthdays elsewhere.

How the test works

• Choose your birth month and day. Adding the year is optional and also shows the weekday you were born on and your age.
• We look up the average number of US births on that calendar day across 15 years and rank all 366 days from highest to lowest.
• Your share of birthdays comes from that day's births divided by all births in a typical four-year cycle. February 29 counts as one day in four years, which is why it is so rare.
• The group odds use your day's share to estimate the chance that at least one other person in a group shares your exact birthday.

Levels

Your score maps to one of 6 levels. These ranges are guides, not official standards.

Tips to improve

• Try your friends' and family's birthdays. The gap between the most and least common dates is bigger than most people expect.
• Check September 9 to 20 and December 24 to 26 to see the two ends of the range.
• Remember the score is a guide: a high rank number means rarer, not better.

Frequently asked questions

What is the most common birthday?

In this US dataset (2000 to 2014), September 12 had the highest average number of births, with several other days from September 9 to 20 close behind. Mid-September dominates the top of the list.

What is the rarest birthday?

February 29 is the rarest because it only exists in leap years. Among regular calendar days, December 25 had the fewest births on average, followed by January 1 and December 24.

Why are holiday birthdays rarer?

Fewer births happen on major holidays. A common explanation is that fewer inductions and scheduled caesarean sections take place on those days, so more births are moved to the days around them.

Is this data accurate for countries outside the US?

No. It reflects US birth records from the Social Security Administration. Many countries show a similar late-summer to early-autumn peak, but the exact ranking differs. Treat results for other countries as a fun estimate.

How is the group odds figure calculated?

We take the share of people born on your date and calculate the chance that none of the other people in the group share it. The probability that at least one does is one minus that. It assumes the group is a random sample of Americans.

Does the year I was born matter?

Not for the ranking, which uses the average across 2000 to 2014. If you add your birth year we simply show the weekday you were born on and your age.