This year my birthday falls on Thanksgiving. It doesn’t happen very often, but when it does it’s kinda fun. I was asked how often it happens, and of course I had to think about it. My first thought was every 7 years (a number I came up with in my youth), but now I’m interested in being more accurate. As a youth I got the general range correct, but forgot about leap year.

So, it really is hard to gauge at first glance. Here’s why. It follows a definite pattern up until leap year. Then all bets are off. According to one site I visited, Thanksgiving falls on November 22 an “average” of every 11 years.

That number seemed questionable to me even though it was “voted” the best answer. So, I kept looking (and calculating).

Here’s the basic pattern. Thanksgiving is on the fourth Thursday in November, and not on a specific date like New Years or Independence Day. These dates range between November 22nd and November 28th. So, my birthday is the earliest possible date for Thanksgiving.

In 2009 Thanksgiving was on the 26th. In 2010 it was the 25th, and in 2011 it was on the 24th. Whoops – 2012 is a leap year, so it skipped the 23rd and goes straight to the 22nd. Ah, now we’re seeing a bit of a pattern. The range is every 7 years, but since leap years occur every 4, we can never be completely in synch.

Assuming that all of the possible dates can fall in a leap year, that means the pattern is something like 1-2-3-skip, but over a sample of 7 possible dates, it’s hard to mentally track. However, If you look at actual dates and the use a calculator, a day will actually only be skipped approximately every 28 years. But, in between, it will occur 3-4 times, depending on the start and end dates of those 28 years.

Which means (again, approximately) my birthday will fall on Thanksgiving an average of every 7 years.

Here’s what my future Thanksgiving birthdays looks like: 2012, 2018, 2029, 2035, 2040, 2046, 2057, 2063, 2068, 2074, 2085, 2091, 2096. The pattern of years between is 6,11,6,5,6,11,6,5,6,11,6,5 and so on. Add up 6+11+6+5, and you get 28. Divide by 4 = 7. On average. So, while I was correct about the number 7 as a youth, I did not realize that I could not just add 7 to this year’s date to get the next one.

Now, the other “milestone” that happens on my birthday, that I really don’t like, is that it is the anniversary of John Kennedy’s assassination. But, that’s a story for another post.

Regardless – happy birthday to me, and Happy Thanksgiving to all of you.