How Common Is it for Siblings to Have the Same Birthday?

This blog post answers the question, “How common is it for siblings to have the same birthday?” Besides that, the blog post provides a few real-life examples of siblings with the same birthday and lists a few things that parents with children born on the same day should consider while planning celebrations. 

How Common Is it for Siblings to Have the Same Birthday?

According to Michael Hutchings, a mathematician at the University of California, Berkeley, the probability of a family with two children having the same birthday is one in fifty thousand. 

However, a Statistics professor named Philip Stark from the same college disagrees with this figure. He feels there are various factors at play to determine the exact odds of a woman bearing two children on the same date but in a different year. Some of these factors include:

  • The mother’s fertility time;
  • The parents’ efforts to try to have their children on different dates; and
  • The duration of the couples’ attempt to conceive

Real-Life Examples

Let us look at real-life occurrences of such a phenomenon in the following months and years.

  • February 1966
  • January 2008
  • January 2011
  • June 2011

February 1966

One family from Clintwood, Virginia, entered into the 1977 Guinness World Records as “the only verified family with five children to share their birthdate.” Five siblings, namely Catherine, Charles, Carol, Claudia, and Cecilia, were born on February 20 in different years; Catherine in 1952, Carol in 1953, Charles in 1956, Claudia in 1961, and finally, Cecilia in 1966.

To top it off, their parents, Ralph and Carolyn Cummins happen to have their wedding anniversary in the same month to top it off.    

In 1977, the record-keepers mentioned that the probability of such an event to occur was 1 in almost 18 billion. Cheryl, one of the five siblings, said that she carries around the 2003 copy of the Guinness Book of World Records as this remarkable feat does not get published every year. She said that she loves letting everybody know about this peculiarity every year on their birthday as nobody can wrap their heads around it.

In the years that mother Carolyn was not bearing a child, she would return home early from work on the 19th of February and bake different cakes for her children. For instance, she would bake a cake that looked like a football field for Charles, roses for Catherine, a doll with a dress for Claudia, and so on. Once, she made a cake displaying the time at which each of her kids was born. 

Carolyn baked a cake every year even after her children left for college. She would put them in the freezer and await her children’s return home for the spring holidays.

The children claim that their mother met all of their needs individually and made them feel unique and special. Claudia mentioned that their shared birthday is representative of the family’s values and a sense of togetherness. 

January 2008

Martin and Kim MacKriell from Tuffley, Gloucester delivered their children, Robin, Rebecca, and Ruby, on the January of 29th in 1994, 1996, and 2008, in that order. Statisticians report that the chances of such an event happening in 7.5 in a million or one in 133,000. 

Kim was due to deliver her youngest child Ruby on the 7th of February. Still, her doctor mentioned that she would have to undergo a cesarean section and the only available date for the surgery was 29th January.

Robin, their son, said that people think it is weird that his youngest sibling shared her birthday with him and his other sibling and urged him and his family to publish this occurrence in the newspaper. He also said that he and his sister used to host birthday parties together but now do separate things on their birthday. He likened their birthdays to Christmas sans trees as they will receive presents on the same day. 

January 2011 

Holly O’Shea was born on the 2nd of January 2011 in Milltown, Dublin, while her two older sisters, Anna and Georgia, were born on the same date but in 2009 and 2007, respectively. These girls were born precisely two years apart. 

Their parents, Mike and Stella O’Shea, claim having not planned for this to happen. They added that Stella had a natural birth for all three of her daughters and that they were all born a week or so after the date given to them by the doctors. 

Mike, the father, stated that his older daughters were delighted to have a new sibling. He added that they were too young to understand the significance of the date as of 2011.

After Holly was born, Stella Googled to see if any other family had achieved this feat, but only found a family with two boys and a girl and another one with three boys born on the same date but different years. 

The family exclaimed that they could not wait to celebrate three different 18th and 21st birthday parties. 

By the name of Rhona O’Connell of University College Cork, Ireland, a midwifery lecturer stated that there is no medical explanation for a lady to birth children on the same date in different years. 

June 2011

A couple from San Jose – Apollo and Kelly Johnsen, gave birth to their daughter on the 11th of June 2011 at 6:49 PM. Their older son was born two years ago on the same date and at the same time. Additionally, they were birthed in the same room at Good Samaritan Hospital, San Jose.

Although the couple wanted to have their two children two years apart, they did not plan to have them on the same date. Such an incident took everybody, including them, the doctors, and their son, by surprise. 

Kelly Johansen did not have a cesarean section. Further, the couples mentioned that they were due to deliver baby Athena on the 10th of June but had to wait until 3:00 AM on June 11th for a delivery room to begin labor. Even Kelly’s cousins, who were twins, were not born simultaneously, as mentioned by the twin’s father (Kelly’s uncle). 

What Should Parents of Children with the Same Birthday Keep in Mind?

When siblings share their birthdays, parents must consider the following while planning celebrations.

  • Finance
  • Age of the Children
  • Consider their Opinion
  • Separate Parties
  • Intuition
  • Guest List
  • Ensure it is Special


The amount of money you can spend on hosting birthday parties play a significant role in determining the kind of party your children can have. If you have budgetary constraints, it is best to host one party with friends and family invited. 

The way your children feel is not based on whether you host separate or combined parties. If anything, different parties could be stressful due to more time, costs, logistics, and even your children comparing each other’s parties. Instead, ensure you make a wise decision for your entire family and imbibe values and lessons for life in your children.

Age of the Children

Younger children typically enjoy joint parties more than older ones. As small kids, they may have fun celebrating together, but as they grow older and become teenagers, they would want to do separate things. You may also consider hosting one joint party with the entire family and individual parties for your children with their friends. 

Consider their Opinion

If finance is not an issue, ask your children what they want and how they feel about separate or combined celebrations. The older they are, the more they are likely to care about their parties, so you should consider their opinions if you can. You may be surprised by how common it is for children to enjoy and want combined parties. 

Separate Parties

Some parents like to host separate parties as they feel their children should feel special. On the other hand, some parents think joint parties are more fun and memorable for each of the children. 


Parents should follow their intuition to decide on the type of parties they want to host for their children. If they are old enough to decide for themselves, that is fantastic. However, if they are too young, go by what you think would fulfill their needs based on their personalities. 

Guest List

Whether you want to host joint or separate parties is also based on the number of guests you might have. Even for children with birthdays close to each other, joint parties are more feasible when guests travel long distances to attend the celebration.  

Ensure it is Special

Ensure that each of your children feels celebrated and special. The siblings must enjoy their birthdays, and one way to ensure this is having a birthday cake for each of them, even if the rest of the aspects are combined. While hosting parties, be sure to call all of their friends. 


This blog post answered the question, “How common is it for siblings to have the same birthday?” The article described a few real-life occurrences of siblings with the same birthday and listed a few things that parents with children born on the same day should consider while planning celebrations. 

If you’ve enjoyed the How Common Is it for Siblings to Have the Same Birthday? mentioned above, I would recommend you to take a look at ‘‘How Common Is it for Siblings to Have the Same Blood Type?‘ too.

Frequently Asked Questions (FAQs): How Common Is it for Siblings to Have the Same Birthday?

What is the term for siblings sharing a birthday?

In the United States of America, siblings sharing a birthday was known as “Irish twins,” but has become somewhat obsolete and is extended to include siblings born roughly a year apart. 

What is the probability of two individuals having the same birthday?

According to the “birthday paradox” or “birthday people,” it is postulated that there is a 50% chance of two people sharing their birthday in an arbitrary group of 23 people.

Which is the rarest date on which a person can be born?

The following are the rarest dates on which a person can be born.
January 1st
July 4th 
December 24th 
December 25th 

What is the smallest gap that siblings can have?

The smallest gap between siblings is, of course, nine to ten months. Although it may be challenging, it can also be satisfying as the siblings tend to experience so much about their surroundings together.  


Daily Mail Reporter. (2008, February 25). Couple gives birth to three children on the same day… 14 years apart. Daily Mail. Retrieved from–14-years-apart.html#StartComments.  

Daily Mail Reporter. (2014, February 22). FIVE of these siblings share the same birthday – and there’s not even a pair of twins! Daily Mail. Retrieved from

Lee, J. J. (2011, June 14). San Jose siblings two years apart, born on the same day at the same time. The Mercury News. Retrieved from,children%20who%20aren’t%20twins

O’Sullivan, M. (2011, January 07). Siblings share same birthday – but two years apart. Independent. Retrieved from

Tom, P. A. (2013, August 21). Should Siblings Celebrate Their Birthdays With the Same Party? Popsugar. Retrieved from