It’s Leap Day, that day when we feel sorry for people born on Feb. 29 because they have a birthday only once every 4 years. Of course, those people are totally partying right now. And remember, when they’re 76, they get to say they’re only 19. In a “leap year” we add an extra 29th day to February — but why? Because the hours counted up by our clocks in a year don’t exactly match the time Earth takes to go around the Sun. Earth ends up about 6 hours behind its spot in space 1 year earlier. That’s 1/4 of a day every year, so every 4th year we make up for it by adding 1 day. The thing is, it isn’t exactly 6 hours that we’re off, so every 100 years we don’t add the leap day…but then every 400 years we have to skip that rule and add it! Over thousands of years, it all works out. The question is, how many leap days have you lived through? You’ll see below that the answer takes some thinking!

*Wee ones:* How old will you be on the next leap day? Count up by 4 years!

*Little kids:* If February has 29 days this year including the extra day, how many days does it have when there’s 1 day less? *Bonus:* How many leap days have you lived through? Whether your age is a multiple of 4 or not, you have to do a little trick!

*Big kids:* How many leap days since your mom/dad/some other favorite older person was born? *Bonus:* Except for non-multiple-of-400 multiples of 100, leap years are the years divisible by 4. Will the year 2030 be a leap year? (Hint if needed: Is 2000 divisible by 4? And if so, can you jump in sets of 4 to get to 30?)

Answers:

*Wee ones:* Different for everyone…count 4 more than your age on Leap Day!

*Little kids:* 28 days. *Bonus:* Different for everyone…If your age is not divisible by 4 (can’t cut it in half twice and get a whole number), find the biggest multiple of 4 less than your age and divide by 4, to get the full sets of 4 years you’ve lived start to finish, then add 1 for today. If you ARE a multiple of 4 today, divide by 4 (the answer includes today), but then add 1 — because you lived on Leap Day when you were 0 years old, too!

*Big kids:* Different for everyone…use the same steps above as you did for your own age. *Bonus:*2030 won’t be leap year, because 2000 is a multiple of 4 (4 x 500), and then 30 adds 7 1/2 sets of 4.

Laura Bilodeau Overdeck is founder and president of Bedtime Math Foundation. Her goal is to make math as playful for kids as it was for her when she was a child. Her mom had Laura baking before she could walk, and her dad had her using power tools at a very unsafe age, measuring lengths, widths and angles in the process. Armed with this early love of numbers, Laura went on to get a BA in astrophysics from Princeton University, and an MBA from the Wharton School of Business; she continues to star-gaze today. Laura’s other interests include her three lively children, chocolate, extreme vehicles, and Lego Mindstorms.