Explore the calendar behind your birthday. Each guide explains what the birth records show, how we compare dates, and where the numbers come from.
Birthday guides
Look up dates and compare months using the historical U.S. baseline.
The most common birthdays
Explore the full birthday ranking, September 9’s lead, and the cluster of September dates near the top.
The rarest birthdays, including leap day
See the least common dates and what changes when you count births per actual February 29.
Birth months and month length
Compare monthly totals with daily averages to see how an extra calendar day affects the ranking.
Birthdays within a month
Compare individual dates with their month rank, yearly rank, and recorded birth counts.
Which April birthday is rarest? All 30 dates ranked
April 1 is the rarest April birthday in historical U.S. records. Compare all 30 dates, their April and overall ranks, and their share of births.
August birthdays ranked: August 3 is the rarest
August 3 has the fewest August births and August 8 the most. Compare all 31 dates and see why August leads in total births but not per day.
Is Christmas a rare birthday? December dates ranked
December 25 is the rarest December birthday in historical U.S. records. Compare every December date, including the late-December dip and December 31.
February birthdays ranked, with leap-day context
Compare all 29 February birthdays in historical U.S. records, including leap day's five actual occurrences and a fair per-occurrence ranking.
January birthdays ranked: January 1 is the rarest
January 1 has the fewest January births and January 24 has the most in historical U.S. records. Compare all 31 dates and find January 8.
How rare is a July 4 birthday? July dates ranked
July 4 is the rarest July birthday and July 7 is the most common in historical U.S. birth records. Compare all 31 dates and see how July 5 ranks.
June birthdays: the rarest and most common dates
June 8 has the fewest June births and June 27 the most in historical U.S. records. Compare all 30 dates and June 8 with nearby dates on the same weekday.
Is March 17 a rare birthday? All March dates ranked
Find the rarest and most common March birthdays, see all 31 date ranks, and learn whether March 17 and March 18 are rare in historical U.S. records.
May 26 and the rarest May birthdays
May 26 is the rarest May birthday in historical U.S. records. Compare all 31 dates and see how its count differs in years when it was Memorial Day.
Thanksgiving dates in the November birthday ranking
Compare every November birthday by recorded births and rank. See why the dates around Thanksgiving need a closer look.
Halloween among October birthdays: all 31 dates ranked
Compare all 31 October birthdays by rank and count. See how Halloween compares with nearby dates on the same weekday in historical U.S. records.
September birthdays: the first week and September 9
Find September's rarest and most common birthdays, and compare its first seven dates with the next seven in historical U.S. birth records.
Individual birthday questions
Holiday dates, unusual rankings, and questions about a particular birthday.
Is an April Fool's Day birthday rare?
April 1 is April's least common birthday in historical U.S. records. Compare nearby dates, other month starts and its yearly same-weekday pattern.
Is August 31 a rare birthday?
August 31 ranks 85 of 366 dates in historical U.S. birth records, despite ranking 26th within August. See annual weekday comparisons and Labor Day exclusions.
How rare is a Christmas Eve birthday?
December 24 ranks 363rd in historical U.S. birth records. Compare Christmas Eve with December 25 and 26, including federal observance years.
How rare is a Christmas birthday?
Christmas Day is the least common birthday that occurs every year in historical U.S. records. Compare its odds, leap day and annual weekday-matched counts.
How rare is a December 26 birthday?
December 26 ranks 360th in historical U.S. births. Compare the day after Christmas with nearby dates and years when Christmas was observed on Monday.
How rare is a December 31 birthday?
December 31 ranks 348 of 366 birthday dates in historical U.S. records. Compare New Year's Eve with Christmas, January 1 and nearby weekdays.
Is Valentine's Day a rare birthday?
February 14 leads February and ranks 62nd in historical U.S. records. See its yearly comparison with nearby weekdays and what separate research found.
Is February 28 a rare birthday?
February 28 occurs every year and sits near the middle of the historical U.S. birthday ranking. Compare leap years, February 29 and March 1.
Is February 3 really nobody's birthday?
February 3 is not an empty birthday date: historical U.S. records contain 228,433 births. Check its rank, nearby dates and year-by-year evidence.
How rare is a New Year's Day birthday?
January 1 ranks 364 of 366 birthday dates in historical U.S. records. See New Year's Day odds, adjacent-date comparisons and annual SSA counts.
Is January 2 a rare birthday?
January 2 ranks 361 of 366 birthday dates in historical U.S. records. Compare January 1, 2 and 3 and separate years when January 2 was the observed New Year's holiday.
Is January 8 a rare birthday?
January 8 ranks 343rd in historical U.S. records. See nearby-date comparisons and why its low rank does not mean fewer births than matched weekdays.
Is July 1 a rare birthday? A common date in U.S. records
July 1 ranks among the more common birthdays in historical U.S. records. Compare July 4 and 7, plus yearly evidence using nearby matching weekdays.
How rare is a July 4 birthday? Independence Day across 15 years
July 4 is the rarest July birthday in historical U.S. records. Explore annual comparisons, the weekend exception, and how July 3 and 5 differ.
Is June 21 a rare birthday? Rank and weekday comparison
June 21 is relatively common in historical U.S. records. Its small nearby-weekday gap changes direction with the comparison window; see the evidence.
Is March 17 a rare birthday?
March 17 is one of March's most common birthday dates in historical U.S. records. See its overall rank and comparisons with nearby weekdays.
Is May 5 a rare birthday? U.S. rank and yearly comparisons
May 5 is near the middle of the historical U.S. birthday ranking. Compare 5/5 with nearby dates and see its mixed yearly weekday-matched pattern.
Is November 11 a rare birthday?
November 11 sits near the middle of the historical U.S. birthday ranking. Compare Veterans Day, federal observed dates and nearby weekdays.
Is November 13 a rare birthday? The date and Friday the 13th
See November 13's historical U.S. birth rank and annual comparisons. Separate the fixed birthday date from its single Friday occurrence in the SSA window.
How rare is a November 26 birthday? When the date is Thanksgiving
See November 26's historical U.S. birth rank and annual counts. Compare the date's one Thanksgiving occurrence from 2000 through 2014 with its other years.
How rare is a November 27 birthday?
November 27 is November's rarest birthday in historical U.S. records. Separate actual Thanksgiving years, the day after, and ordinary years.
Is November 29 a rare birthday?
Compare the latest possible day after Thanksgiving with ordinary November 29 dates in historical U.S. records.
Is October 13 a rare birthday?
October 13 ranks 317th in historical U.S. births. Compare nearby dates and actual Friday-the-13th years without confusing a date with its weekday.
How rare is a Halloween birthday? October 31 across 15 years
October 31 is the rarest October birthday in historical U.S. records. See whether Halloween's lower birth count appears each year after matching weekdays.
Is September 11 actually a rare birthday?
September 11 ranks 91st in historical U.S. birth records. Compare nearby September dates and see its yearly pattern without assuming a post-2001 cause.
Calendar calculators
Browse all birthday calculators , including the rarity checker and birthday paradox.
Find a birthday milestone. Your date stays in your browser.
What weekday was I born?
Find your birth weekday with Gregorian calendar arithmetic. See complete examples and leap-year rules.
Diamond and platinum birthday calculator
Compare different milestone meanings and find the date under a stated calculation rule.
Half-birthday calculator
Compare six calendar months with halfway between birthday anniversaries, including month-end and leap-day dates.
Golden-birthday calculator
Find the year your age matches your birth day, with a clear explanation of the calendar convention.
Original research
Original comparisons with their source periods, calculations, and limitations.
Are birthdays evenly distributed through the year?
U.S. birth records from 1994 through 2014 show how many birthday dates differ from an even distribution, with leap-day and weekday comparisons.
Birthday paradox: what are the odds of a shared birthday?
Use the birthday paradox calculator, follow a worked 23-person formula, and compare match probabilities with expected matching pairs and historical U.S. birth shares.
Rarest and most common birthday in every month
Find each month's most and least common birth date in historical U.S. records, with a fair comparison for leap day.
Did birthday rankings change over time?
Compare U.S. birthday rankings in 2000 to 2004 and 2010 to 2014, and see how weekday composition changes the comparison.
What day of the month has the most births?
The 20th had the highest daily average in U.S. SSA birth records from 2000 to 2014. See all 31 numbered days and why the answer changes with the method.
Are fewer babies born on Friday the 13th? A 15-year U.S. comparison
Compare all 25 Friday-the-13th dates in SSA U.S. birth records from 2000 through 2014, including annual results and Thanksgiving-control sensitivity.
Which holidays have the fewest births?
Christmas has the fewest births among four selected fixed-date U.S. holidays in SSA records from 2000 through 2014. See the counts and nearby-date comparisons.
How many people share your birthday?
See actual counts in historical U.S. birth records and expected matches in a hypothetical group. Learn why neither gives an exact worldwide count.
How do leap-day birthdays work?
A February 29 birthday doesn't mean aging only once every four years. See a worked calendar, upcoming leap days, and ways to celebrate in common years.
Are fewer babies born on Memorial Day?
Memorial Day averaged 35.3% fewer recorded births than nearby Mondays in U.S. SSA data from 2000–2014. Compare every holiday date and year.
Does September 9 have the most births every year?
See the most common birthday in each year from 2000 through 2014, how September 9 ranked, and why the day of the week changes the comparison.
What is the rarest zodiac sign by U.S. births?
Compare the 12 sign date ranges by recorded births per day, 1994–2014. See how the sign dates and holidays change the result.
How rare is it for siblings to share a birthday in different years?
Understand the 1-in-365 independent benchmark for non-twin siblings, how known dates change the odds, and why it is not a measured rate for real families.
How many babies are born on Thanksgiving? A 15-year U.S. comparison
See how births on each Thanksgiving from 2000 through 2014 compare with nearby Thursdays in U.S. records, with a full year-by-year table.
What are the odds that three people share a birthday?
Separate three specified people sharing a birthday from any triple in a group. Compare exact classic probabilities with historical U.S. birth-share weights.
What are the odds that two people share a birthday?
Compare a match to your own birthday with a match between two random people. See the classic odds and a model based on historical U.S. birth shares.
How many babies are born each day in the U.S.?
Use NCHS provisional birth data to find the U.S. daily average and see why the actual count varies by date.
Most common day of the week to be born
Tuesday leads daily births in U.S. SSA records from 2000 through 2014. Compare weekday and weekend averages, then see how their gap changes year by year.
For source files and definitions, read the methodology .