The Same Birth Date

Thursday, June 19, 1986

On June 19, 2015, I met with a new friend for coffee to discuss my upcoming talk on coincidences. He knew the audience well and could help guide me to better communicate with them.  He was also interested in knowing more about Coincidence Studies.

He started the conversation with “today is my son’s 29th birthday” and then described his continuing amazement at how quickly time passes. Startled, I waited until he finished to tell him that today was the 29th birthday of one of my sons.  Our sons were born on the same day!

Earlier that day, I had finally completed a four month negotiation to settle an ugly dispute with a business associate.  It was a great relief to have agreed on a final dollar number.

On my son’s birthday, I received two presents—an improbable birthday coincidence and finalizing an agreement to receive a substantial amount of money.

How did it happen that I received two such great presents on my son’s birthday?


Base rates

Sons having same birth date. Millions of people were born on June 19, 1986. What are the odds of two people 5 years apart in age having a child with the same birth date?  Not birthday but birth date.  Not particularly unlikely given their closeness in age.

Meeting on their birthday. It was a convenient Friday for my friend and me to meet. We did not see each other regularly. This was only the second time we had met outside of social gatherings. Did I pick the day in part because it was my son’s birthday? The likelihood of our meeting on their birthday was about 1/365.

Discussing the birthday. What are the odds that one of us would bring up the birthday of his son? Pretty high because it was close to the surface for each of us.

So the key question is what are the odds of two people within 5 years of age having children with the same birth date meeting on their children’s birthday and discussing it?  Not so astronomical actually. Still pretty amazing.

Discussing Coincidences. I write and email about coincidences but rarely meet with the primary purpose of talking about them. Lately, I have avoided discussing the idea unless someone else does. So to meet to discuss coincidences was unlikely.

Reaching a settlement on my son’s birthday. The business problem had been going on for four months. Lots of verbal pushing and threatening. Earlier in the week I threatened my adversary for a third time. After avoiding any negotiation, he finally agreed to discuss a settlement figure with me. From past experience, I knew that Friday was the day he liked to have these discussions. The Friday of that week was June 19.  So I picked the week to do the third threat that had the Friday that was my son’s birthday. Yet I was not at all confident that he would be willing to negotiate with me.

My son was very much involved with my initiating the settlement conflict. He was my advisor at the beginning of the dispute. I had wanted him to do the deal for me because he is a better negotiator. 

Probability summary

There is a moderately low probability for each of us to have sons with the same birth date. Meeting on their birthday, decreases the coincidence probability. That we were together to discuss coincidences decreases the probability even more.

There was no guarantee that my adversary would negotiate that week. But if he were going to, then it would most likely be on the Friday of that week, June 19.  This element lowers the total coincidence probability even further.


Personal contributions
I had something to do with creating both coincidences. I picked June 19 to meet with my friend and selected the June 19th week to hopefully finalize the negotiation.

The purpose of the meeting was to discuss my first formal coincidence lecture.  Coincidences seem to be increase during transitions. 

In addition to probability and my own decision making, I feel that something else I don’t know about, a mystery, made some contribution.  The probabilities seem too low to just attribute to chance and to me.

The coincidence increased my feeling of connection with my son. He had been so helpful with the difficult negotiation.  It also raised a question about my new friend because he had been involved with another meaningful coincidence of mine. Is he a coincidence magnet for me?

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