# How many people were born on my birthday?

And how would you figure this out? What equations would you use? What data would collect? I don’t mean the average amount of people born each day (although that would be interesting) I mean the number of people born on a particular day worldwide.

Here is a fun site.

I share a b-day with ** Ozzy, Julianne Moore and Daryl Hannah**

I’m not sure you can get that specific. Here are my numbers.

Assume the population grows at 3 percent globally. Assume 5.5 Billion people on the earth when you were born. So 3% of 5.5 Billion is 165 million people born that year. Divide by 365 gives you about 500,000 people a day.

So aside from half a million other people, you’re special.

There are actually 366 birthdays.

…and, since those 500,000 all share the same astrological sign and birth date, they will all have the same personality and the same fate!

At least one

This is quite an interesting site considering the probabilties of how many people share birthdays. They reckon in a room of 23 people, there is a greater than 0.5 probabilty that two share a birthday.
http://www.richland.cc.il.us/james/ictcm/birthday.html

12 people were born on your birthday

I am not sure if the question is how many people were born on Jan1 or on Jan1, 1985.

If the former I doubt that you will do better than find the most precise population of the Earth you can and divide by 365 and find some way to factor in leap years – maybe by using Grey’s numbers and … figuring LY in … I am no where near smart enough to do that for you. I think that inexact number is about as close as you are ever going to get tho.

If the question is Jan 1, 1985: You can use Grey’s numbers and look at historical data, if there was a horrific war somewhere (WWII, I China) or a 30’s style Ukrainian famine, that might be enough to need to be factored in. In the end that number too will be based on averages and best guess and you still won’t have a locked down 100% no-doubt number.

You are going to have to accept some margin of error.

I was thinking along the lines of Jan 1 1985.

Are there records kept of how many people were born in a particular country on, say, 1/1/85? Or can it be found with some research how many people were born in London, New York and other major cities and a few small villages on one particular day and then extrapolate?

Even if there are records in all the countries that keep records, you’d have all those places that either didn’t keep records or that have lost them. The best you’ll ever get is an estimate, and the best one in your case might just be to find the population of your state/province/whatever on that date and divide that by 366, although the chances of somebody being born on Feb/29 are not as good as any other date. But since an estimate is all you’ll have anyway, that trivial difference won’t affect the estimate all that much.

What am I missing Zeldar? Why 366, we’re not counting un-birthdays are we?

In a leap year, there are 366 days.

Yeah. :smack:

Ok change my numbers by dividing by 365.25.

That’s still not covering the fact that a Feb/29 birthday only happens once every four years, so it’s less likely than any other day, and as a consequence, any day but Feb/29 has a greater chance than Feb/29. So the 365.25 answer is close (probably close enough for this estimate) but still not 100% accurate.

With the population of the state/province as a basis, you still can’t get the number born on the specific date Jan/1/85. To do that, you’d need the sort of actuarial tables that insurance companies use.