Isn’t it kind of strange that one of the most important days of your life — the day you were born — is nothing but a blur to you? You don’t remember any of it! Of course, that’s to be expected, since you were so new to the world and didn’t even know how to talk, walk, or read yet!

Ever since that day, you’ve probably celebrated the anniversary of that day once each year. What are we talking about? Your birthday! You know, that day when you get cake, ice cream, and all those presents?

Would you believe that some people actually celebrate TWICE each year? Not only do they celebrate the anniversary of the day they were born, they also celebrate six months later on their half birthday!

What brought about such craziness? Is it a desire for more presents? An excuse to have another party? Or are there some valid reasons to celebrate half birthdays?

Before we get to the reasons, let’s take a look at how half birthdays are calculated. Yes, some math is involved, so put on your thinking caps.

There are a couple of ways to calculate half birthdays. The first — and easiest — is simply to keep the same number of the birth date and add six months to it. For example, if your birthday is January 13, then your half birthday would be on July 13.

Of course, this easy method doesn’t always work, because not all months have the same number of days. For example, an August 30 birthday would become February 30 — a day that doesn’t exist!

If you want to be really precise, you need to add half the number of days in a year to your birth date. In a normal year, this means adding 182.5 days. In a leap year, you would add 183 days. If this sounds too complicated, don’t worry. There are plenty of websites that will do the work for you!

So what about those good reasons for celebrating half birthdays? For starters, consider kids. As they grow, six months can mean huge milestones. It can be a special time to celebrate with them as they grow up, because they grow up all too fast!

Half birthday celebrations can also be great for those people whose regular birthday might be overshadowed by a nearby holiday, such as Christmas. Likewise, kids whose birthdays fall in the summer might enjoy celebrating their half birthdays, so that they can share their joy with their friends at school.

Half birthdays aren’t the only special “birthdays” that some people celebrate, though. Adopted children sometimes celebrate both their actual birthday (the day they were actually born) and the day they were adopted. Do you have any other special “birthdays” that you and your family celebrate?

36 Join the Discussion

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    • The clues about today’s Wonder were tricky, Alexis, and we’re so glad you’re here with us today! :)

      We Wonder if you have ever celebrated your own half birthday… we bet it would be a blast! Thanks for sharing your awesome guesses for tomorrow! :)

  1. Dear Wonderopolis,
    I loved that video. Lucas with that monkey they make a prefect match. I thought it would be a pair of shoes or pants. Thanks for reading!

  2. This was such a cute video the little boy with his sock monkey put the whole video together those parents must love him. You got me stumped yesterday nice work!

    I think tomorrow’s wonder is about the weather!!!

  3. I never knew that some people celebrated their HALF birthdays! I just thought it was a special TYPE of day I thought it shouldn’t be celebrated TOO much. :)

  4. Dear wonderopolis, this is my first time at wonderopolis. Today’s wonder is so boring who wants to see a baby grow up to 6 moths why not like 10 years!? Mrs. Wall and her class yay I’m writing on wonderopolis. My aunt passed away that’s why I’m not there.

    I think tomorrow’s wonder will be something to do with water.

    • Hey there Jacob C! We’re keeping you and your family in our thoughts, but thanks for WONDERing with us! We appreciate your comment! :)

  5. I also celebrate my ‘everything’ birthdays. A bit ago, I was ’50 everything': 50 years + 50 months + 50 weeks + 50 days + 50 hours + 50 minutes.

  6. Your video was so funny! Lucas’ facial expressions made us crack up! It was sweet how Lucas was holding the monkey’s hand. I like how adopted kids celebrate their adoption day and their b-day! Daniel likes the idea of celebrating his real b-day and half birthday because…DOUBLE the PRESENTS!

    • Thanks for WONDERing with us, Mrs. Albani’s Class! We’re so excited that our Wonder Friends have been using their imaginations about half birthdays! WOHOO! Also, we think Daniel’s idea is pretty clever– talk about lots of presents! Phew! :)

    • You’re correct, Kade– your half birthday is September 25! We Wonder what you like to do to celebrate your birthday? :-)

    • That’s right, Ann! Unfortunately, you just missed your half birthday. Yet, you can always celebrate next year! Thanks for WONDERing with us today! :-)

  7. This is a cute wonder of the day! I miss the old format of Wonderopolis. Is there a way I can make the text wider so that it fits more of the screen?


    • Hi, Dani! We are so glad that you enjoyed this Wonder! Unfortunately, there is not a way to reformat the current setup on the website. However, you can hold down the “Ctrl” button on your keyboard and press the “+” sign at the same time. This will make the page larger for you to see. We hope this helps! Thanks for WONDERing with us Wonder Friend! :-)

  8. Question: If people celebrate half birthdays now, I wonder if some people would or do celebrate quarter birthdays?

    Ah-ha moment: I knew that in the quiz they would have asked whats the easiest way to measure your half- birthday.

    Text To World Connection: Many people in the world including my friends and I celebrate their birthdays.

    • WONDERful Question, Rushmiah! We bet there are some people that do celebrate quarter birthdays. Thanks for WONDERing with us today! :-)

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Have you ever wondered…

  • When is your half birthday?
  • Why do some people celebrate half birthdays?
  • What other special “birthdays” do people celebrate?

Wonder Gallery customVimeo Video

Try It Out

Are you read to party like it’s your half birthday? We are! Grab a friend or family member and check out the following fun activities:

  • When is your half birthday? Don’t know? Do the math! If you want, you can calculate it using one of the ways described in today’s Wonder of the Day. If you want the answer quickly without the math, just try the handy, dandy online Half Birthday Calculator! Help your friends and family members calculate their half birthdays, too. You never know when your birthday might coincide with a friend or family member’s half birthday. You might be able to combine parties in the future!
  • If you’re wild and crazy enough to celebrate half birthdays, then you’re probably creative enough to come up with some interesting ways to celebrate. Do you get half a birthday cake? Do you cut your candles in half? How about half a bowl of ice cream to go with your cake? What other crazy ideas can you come up with? If you have some great ideas for how best to celebrate a half birthday, post them on Facebook to share with your Wonder Friends. We can’t wait to read your ideas!
  • Up for a challenge? Do some math and calculate when your ¼ and ¾ birthdays would be. It might be a little greedy to ask for four birthday parties each year, but it wouldn’t hurt to know when your quarter birthdays are! Doing the math can be fun, and you’ll be able to track more closely your progress to your next celebration milestone!

Still Wondering

Check out Illuminations’ Birthdays and the Binary System lesson to learn about patterns and place value in the binary system.

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