Binary Dates

There’s a strange meme going round that today is the last “binary date” for a hundred years. I’m not sure where it came from but a couple of people have repeated it on Twitter over the last couple of days.

A binary date is one which is made up completely of ones and zeroes. So in order to find any we’ll need to ignore the “2” in “2010” and assume that we’re writing dates in the shorthand dd/mm/yy format – or your local variation thereof.

In that form we can easily agree that, yes, 11/01/10 is a binary date. And so was yesterday (10/01/10) and the 1st of January (01/01/10). But to suggest that there are no more for a hundred years is clearly nonsense. Anyone suggesting that is guilty of not giving the matter the smallest amount of thought.

There are still six more binary dates to come this year (01/10/10, 10/10/10, 11/10/10, 01/11/10, 10/11/10 and 11/11/10) and another nine to come next year (01/01/11, 10/01/11, 11/01/11, 01/10/11, 10/10/11, 11/10/11, 01/11/11, 10/11/11 and 11/11/11).

After 11th November next year, there will be no more binary dates until the year 2100.

If you’re going to pass on memes, at least check them for accuracy first.


  1. Of course, 01/01/(21)01, and all other variations of 10 and 11 instead of 01 are within 100 years, up to 11/01/(21)10, so there’s a load more for you.

  2. And we’re forgetting that 00 is a valid value in our abbreviated representation of years. So there were nine binary dates in 2000 (01/01/(20)00, etc) and there will be nine in 2100 (01/01/(21)00, etc).

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