Most Common Birthdays: All 366 Dates Ranked by US Birth Data

The most common birthday in the United States is 9 September. Across 21 years of US birth records (1994 to 2014), that date averaged 12,344 births, 10.6% more than a typical day. Mid-September owns the top of the list: 13 of the 20 most common birthdays fall between 8 and 26 September. The least common birthday is Christmas Day, which averaged just 6,601 births, about 41% below normal.

We ranked all 366 dates ourselves from FiveThirtyEight’s public births dataset, which repackages daily counts from the CDC’s National Center for Health Statistics (1994 to 2003) and the Social Security Administration (2000 to 2014). That is 85.7 million births over 7,670 days.

The 20 Most Common Birthdays in the US

Each date is ranked by how far its births sat above or below the average day of the same year, averaged over all 21 years. That adjustment stops a date from looking popular simply because it fell in a high-birth year. The “average births” column is the plain mean count for the date.

The spread at the top is narrow. Number one beats number ten by only 2.3 percentage points, and the order shuffles depending on the source. Run the SSA years alone and 12 September comes first; run the CDC years alone and 19 September wins, with 9 September down in ninth. What never moves is the cluster: every version of the list is dominated by the second and third weeks of September.

Three outsiders deserve a note. 7 and 8 July rank 7th and 16th, right after a 4 July holiday that suppresses births, which fits the idea of deliveries being pushed to the next working days. 19, 20 and 29 December are there for the same reason in reverse: deliveries brought forward before Christmas and caught up straight after it.

The 20 Least Common Birthdays and the Holidays Behind Them

Nearly every rare birthday is a public holiday or sits next to one. Six of the bottom 20 are dates in the 22 to 28 November window where Thanksgiving falls. 31 October (Halloween) ranks 357th, 1 April ranks 353rd, and 26 May, which some years lands on Memorial Day, ranks 350th. Christmas Day is in a class of its own: about 1.87 times as many people were born on 9 September as on 25 December.

How Common Is Your Birthday? All 366 Dates Ranked by Month

Find your month across the top and your day down the side. A low number means a crowded birthday; a number above 300 means you share it with relatively few people.

Two patterns jump out of the grid. Single-digit and teen ranks sit mostly in July, August and September, with a few December dates either side of Christmas, while the 300-plus ranks bunch around late November, the last week of December and the first two days of January. Elsewhere, most dates sit within a few per cent of average, so rank 120 and rank 220 differ little in real terms. If you want to know your exact age to the day on top of how common your birthday is, our age calculator works it out.

Why September Is the Most Common Birth Month

September averaged 11,811 births a day, 10.2% more than January’s 10,721. Count back roughly 39 weeks from mid-September and you land in mid to late December, the holiday season. Research supports the seasonal part of that explanation.

A Boston University School of Public Health study published in Human Reproduction followed 14,331 women trying to conceive in North America and Denmark. Couples had the best chance of conception in late November and early December, and fecundability (the per-cycle probability of pregnancy) fell in late spring. Among the North American participants, season shifted fecundability by 16%; in the southern US the swing was 45%. That biological pattern lines up neatly with a late-summer and September birth peak.

Behaviour plays a part too. In England and Wales, the Office for National Statistics points to parents who may plan births for the start of the school year, citing Institute for Fiscal Studies research, and notes that its top date sits 39 weeks and two days after Christmas Day. Our view: the US data supports both forces. The whole of July to September runs above average, which looks seasonal, while the sharpest single-date spikes cluster in the second and third weeks of September, which looks like holiday-season conception layered on top.

Christmas, New Year, 4 July and Thanksgiving: The Holiday Birth Dip

Holidays fall on different weekdays from year to year, so to isolate the holiday itself we compared each holiday with the average of the same weekday in the same month and year (excluding the holiday).

The weekday-adjusted column tells a cleaner story. New Year’s Eve looks rare in the raw ranking, yet it matches an ordinary day of the same weekday; its low rank comes from sitting in a quiet week. Halloween, by contrast, really is avoided, with about 12% fewer births than comparable days. Valentine’s Day goes the other way and gains 5%.

Thanksgiving Week, Day by Day

Thanksgiving moves between 22 and 28 November, so it drags down a whole week of dates. Aligning each year to its actual holiday shows the pattern.

The Tuesday before Thanksgiving is one of the busiest days of the American birth calendar, 21% above average. Thanksgiving Thursday drops to Sunday levels. Other November Thursdays in the data ran 12.4% above average, so the holiday costs that Thursday about 40% of its usual births. The same squeeze shows up around Christmas: births run 5% to 8% above average on 18 to 21 December, collapse on 24 to 26 December, then rebound to 5% to 7% above average from 27 to 30 December.

Weekday Births: How C-Sections and Inductions Shape Birthdays

Saturdays and Sundays make up 28.6% of the week but only 20.8% of births in our data, and the weekend gap widened over time: weekend days ran 20.5% below average in 1994 and about 31% below by 2009, before easing slightly to 28.3% below in 2014.

The reason is the share of births that are planned. The CDC reports a caesarean rate of 32.4% of US deliveries in 2024 (1,173,391 caesareans). Induction of labour has climbed too: from 9.6% of singleton births in 1990 to 23.8% in 2010, according to an NCHS data brief, and from 24.9% in 2016 to 34.5% in 2024 in a March 2026 NCHS brief. The timing data shows the scheduling at work. In the CDC’s analysis of 2013 birth certificates, 14.3% of caesareans with no trial of labour happened in the 8 a.m. hour alone, while spontaneous vaginal births spread far more evenly across the clock.

This weekday effect is why the ranking needs many years. Any single date moves through all seven weekdays over 21 years, roughly three times each, so the day-of-week swings mostly cancel out. A list built from one year would mostly be a list of Tuesdays.

Friday the 13th Births: A Measurable Avoidance

The period contains 35 Friday the 13ths. We compared each one with the average of the Fridays a week before (the 6th) and a week after (the 20th) in the same month. Every single one of the 35 had fewer births than its neighbours, by 6.4% on average.

Part of that is a general 13th effect. Using the same 6th-versus-20th comparison, 13ths falling on other weekdays averaged 1.9% fewer births. Friday the 13th roughly triples that dip. Since nobody can stop spontaneous labour for superstition, the gap almost certainly comes from planned deliveries booked onto other days, whether by parents or by doctors.

How Rare Is a 29 February Birthday?

It depends which question you ask. Per occurrence, 29 February is only mildly unusual. In the five leap years in the data (1996, 2000, 2004, 2008 and 2012), it averaged 10,512 births, against 11,451 on 28 February and 11,565 on 1 March in those same years. On the year-adjusted measure it ranks 347th of 366, and after correcting for which weekday it fell on, it ran 7.7% below comparable days.

Over a lifetime, though, it is easily the rarest birthday because it exists once in four years. Of the 85.7 million births in the data, 0.061% fell on 29 February, or about 1 in 1,631. A typical date holds about 0.274%, or roughly 1 in 365. Five leap days is a small sample, so read the per-day figure as a fair estimate rather than a precise one.

Novelty Dates: 9/9/09, 11/11/11 and 12/12/12

The single busiest day in the whole dataset was Wednesday 9 September 2009, with 16,081 births. Repeating-number dates attract births well beyond what their weekday would predict, which points again to scheduling.

11/11/11 stands out at nearly 31% above an ordinary Friday that November. The 2009 spike also helps explain why 9 September tops the combined 21-year ranking: one exceptional year nudged an already strong date into first place.

Most Common Birthdays in England and Wales

The UK pattern is similar but slightly later. The ONS analysis of births in England and Wales from 1995 to 2014 found 26 September the most popular birthday, with around 2,000 births on average against roughly 1,800 on an evenly spread day. Eight of its top ten dates fell at the end of September and the other two in early October. Six of the ten least popular dates fall over Christmas and New Year, and 29 February has the fewest births in total.

The September peak sits about two and a half weeks later in England and Wales. Readers tracking naming trends across countries can compare it with our roundup of top baby girl names by country, also built on official statistics.

The Birthday Paradox With Real Birth Data

The birthday paradox says a room of just 23 people has a better-than-even chance that two share a birthday. The textbook version assumes all 365 days are equally likely. Since real birthdays are lumpy, we recalculated it with the actual US distribution, including 29 February at its true weight, using an exact formula in Python.

Uneven birthdays always raise the odds of a match, but here the bump is tiny: 0.05 percentage points at 23 people, because most dates sit close to average. The paradox works because the number of possible pairs grows fast. Twenty-three people form 253 pairs, and each pair is a fresh chance of a match. If you want to sanity-check odds like these by hand, our percentage calculator handles the conversions.

How We Built the Birthday Rankings

• Data: FiveThirtyEight’s two daily US birth files, one from CDC/NCHS (1994 to 2003) and one from the SSA (2000 to 2014). Where they overlap, SSA counts run about 2% higher, so we used CDC for 1994 to 1999 and SSA for 2000 to 2014 to avoid double counting.
• Period: 1 January 1994 to 31 December 2014, 7,670 days and 85,712,738 births.
• Ranking measure: each day’s births divided by that year’s average daily births, then averaged per calendar date. This removes the effect of birth totals rising and falling between years.
• 29 February: averaged over its five occurrences only, so it is compared fairly per day, with its lifetime rarity shown separately.

The rankings describe people born in the US between 1994 and 2014. Induction rates have risen sharply since 2014, so the scheduling effects shown here are unlikely to have faded. For more data-led reads on family life and names, browse our Lifestyle section or the list of boys’ names starting with A.

Birthday Frequency Questions

What Is the Most Common Birthday in the US?

9 September, with an average of 12,344 births a day across 1994 to 2014. 19 September and 12 September are almost tied with it.

What Is the Least Common Birthday?

Per day, Christmas Day, with about 41% fewer births than average. Over a lifetime, 29 February is rarer because it occurs once every four years: about 1 in 1,631 US births.

Why Are So Many People Born in September?

Mid-September is about 39 weeks after the December holidays, and research from Boston University found conception chances peak in late November and early December.

What Is the Most Common Birth Month?

September, at 11,811 births a day on average, followed by August and July. January is the quietest month at 10,721 a day.

Which Day of the Week Has the Most Births?

Tuesday, at 14.9% above average. Sunday has the fewest, at 31.6% below, because planned caesareans and inductions are booked on weekdays.

CDC, SSA and ONS Birth Records Plus NCHS Induction Briefs

• FiveThirtyEight: US births data, CDC/NCHS 1994 to 2003 and SSA 2000 to 2014 (GitHub)
• Office for National Statistics: How popular is your birthday? (England and Wales, 1995 to 2014)
• CDC FastStats: Births, method of delivery (2024 data)
• NCHS Data Brief 554: Induction of labor increases in the United States, 2016 to 2024
• NCHS Data Brief 155: Recent declines in induction of labor by gestational age
• NCHS Data Brief 200: When are babies born? Birth certificate data for 2013
• Boston University School of Public Health: Late fall may be best time of year to try to conceive (2020)