The Half Birthday Calculator
What is a half birthday and why do I care?
A “half birthday” is when you are x.5 number of years old. There are a number of reasons why people want to know about their half birthday:
- Their actual birthday is close to or on another significant date like Thanksgiving or Christmas so they never get the kind of birthday treatment that other people enjoy on non-significant dates;
- They can’t wait for their actual birthday because they have something they want to buy for themselves and need an excuse;
- They just want to have a party and this is a good excuse!
Do you really need an excuse?
Can’t I just add 6 months to get my half birthday date?
No, it isn’t that easy if you want to be accurate. Months have different numbers of days in them with February being the wildest with 28 or 29 days depending on whether is it s leap year or not. Also, the year has more days in the second set of six months (there are more days between July 1st and December 31st than there are between January 1st and June 30th) so depending on the time of year a birthday happens, the half birthday may not be just six months away and it may vary depending on leap years.
The variable number of days in each month combined with the variability of leap years makes the calculation much more difficult than just adding 6 months. For example, in 2020 the half birthday for January 1st is on July 1st because 2020 is a leap year. On non-leap years the half birthday is July 2nd.
Is the calculator really accurate?
Yes. If you think it isn’t let us know why.
If it is so accurate, how come the number of days to/from a particular date is different than what the countdown page says?
The Countdown page has to keep track hours, minutes and seconds while the Birthday Calculator only cares about days. Any portion of a day to the Birthday Calculator is counted as a whole day.
So, if the Half Birthday Calculator says that a date is 10 days away, the countdown clock is going to show you 9 days plus some hours/minutes/seconds. Only at the stroke of midnight will the two agree on the number of days – but only for a second. Actually, we aren’t that sure about the last sentence – we haven’t tested it. If you know what it does, let us know.
If half a year is 182.5 days what happens to the .5 part?
The extra half of a day is not taken into account because the time you were born doesn’t matter for most uses. For example, driver’s licenses don’t have a time of birth on them. When someone turns 21, they do so at midnight (local time) on their birthday – not at the time they were actually born.
It would be really complicated to calculate your actual age down to the second (or even hour) because of several factors:
- What time zone were you in when you were born? If you aren’t still in that time zone, it gets complicated.
- Was daylight savings time or some other offset in effect when you were born? The dates that these offsets are introduced change relatively often and are not at all consistent around the world. Some years they skip them altogether. This makes it very complicated.
- How many leap-seconds have been added or subtracted since you were born? They add or subtract seconds every now and then (there is no set schedule) based on astronomical observations. There is no good way to keep track of these extra seconds.!
- Do you know what time you were born – really? Was the clock whoever recorded the time checked accurate? Did the person recording the time do it at first breath, cutting of the cord, crowning? Did they write it down right away or later? Did they write it down correctly?
There are too many opportunities for error and it doesn’t really matter.
Because the day starts at 00:00:00 (midnight), adding the extra 12 hours (that pesky .5 days) doesn’t change the date, so we can ignore it.
How do you handle February 29th birthdays?
If you were born on February 29th (a leap year birthday – “Leapling” or “Leaper” – which we personally don’t like the sound of) we consider your birthday to be March 1st in non-leap years because we are counting days.
Legally, most jurisdictions will go back to the last valid day of the month – February 28th. This is probably due to the fact that before EventCalc, accurately determining the real half birthday was just too hard.
If you want to be like those faceless bureaucrats that can’t be bothered with accuracy and think that Feb 28th is a good substitute for Feb 29th, then just subtract one day from what the calculator gives you or put in the 28th as your birthday (we won’t tell anyone if you don’t.) But remember that you will actually be younger than you are pretending to be and, as you get older, that will start to bug you.
What about leap seconds?
Luckily, we don’t go into that level of granularity since leap seconds are not a predictable occurrence like leap years are. We only care about whole days and adding or subtracting seconds only makes your half birthday a little longer or shorter.
When do leap years happen?
Leap years are any year in the Gregorian calendar that is divisible by 4 except centenary years (even 100’s) that are not divisible by 400.
In other words, any year evenly divisible by 4 (1984, 1988, 1992, etc) except for those that are an even hundred and NOT divisible by 400. 1900 was not a leap year (1900 / 400 = 4.75) but 2000 was a leap year (2000 / 400 = 5). They are also called “bissextile years”.
Why did you create this calculator?
During a dinner conversation one summer evening, there was a rather heated argument about the proper way to calculate a half birthday (or half anniversary, etc.). This calculator was the result. It actually started out as a really simple (but just as accurate) calculator that has been improved over the years. It is incredibly popular so there is an obvious interest in half birthdays. Who would have thought?
Why all the ads?
The Half Birthday Calculator and other date based tools we offer cost money to host and support but we offer them to you for free. To help pay for the site we include advertisements. Each time you visit the site we get a couple of fractions of a penny.
We are careful to only allow certain kinds of advertisers and products but we want to know if you see an ad that offends you or you think is inappropriate.
When you click an ad you help us keep this service free. If you use an ad blocker, consider buying us a coffee. We won’t actually buy a coffee, we’ll use the money to buy hosting time. Thanks!
The Anniversary Calculator
What does it do?
It will tell you when your next anniversary is and how many years it represents plus what day of the week it falls on. Hopefully this will give you some help in planning for the special day.
Also, it will tell you how long it has been since the date itself and, because we can, when the next (or last) half-year anniversary is (or was). Imagine how special it would be to be surprised about a half-anniversary. Awwww.
Can’t I do this with a calendar?
Sure, but it isn’t as easy. And you are here already.
Is the calculator really accurate?
Yes. (See the same question in the Birthday Calculator section for more incredibly boring information.)
The half anniversary isn’t very accurate – what about the half day?
Check out how we calculate half days in the Half Birthday Calculator section.
How do you handle February 29th anniversaries?
If the anniversary falls on February 29th we consider the anniversary to be March 1st in non-leap years because we are counting days.
What does it do?
You enter a date and, optionally, a time that you want to count down to and we’ll display how long you have until that date (and time) arrives. Or, enter a date in the past and we’ll show you how long it has been since then.
You get a page with a link that will always display your countdown (count up?) so you can bookmark the page to make it easy to go back to or send it to your friends. You can give it a title so you know what’s what.
So it will count down to a date in the future or up from a date in the past?
Yes. It will “roll over”, too. So when your appointed time arrives it will start counting up from that point.
Is it accurate?
It is as accurate as your host device (computer, smart phone, etc.) It gets it’s time from your device so if the time is off on your device, the countdown will be, too.
Timezones can play havoc with countdowns, too. If you set up a link then change the time zone you are in, the link will be wrong by the difference between the original and new time zones.
Is there any limit to the number of countdowns I can have?
No. You are only limited by the number of links you want to keep track of.
What are Reminders?
Reminders are just that – a reminder of a date that you want to remember. Let’s say you find out when your friend’s half birthday is but it is months away. Set up a reminder and we’ll send you an email or text message when the date approaches. They can be set up for anything you want to be sure not to miss.
How many reminders can I set up?
As many as you want. Each date can have three reminders: one week before the date, two days before the date and on the date itself. This should give you enough time to prepare for the big day.
My mobile phone provider isn’t listed – what do I do?
You could go with just an email message or, if you know the email-to-SMS gateway address, you could try entering that in the email box. Most carriers have an email address that you can send a message to that are turned into text messages. Check with your carrier to see if they have something like that. If you figure it out, let us know and we’ll add it to the list.
When do you send the reminders?
You can remind yourself of one date up to three times: one week before (-7 days), 2 days before and on the date itself.
We try to send out reminders starting at about 8:00 am local time but it may be a later depending on how many we have to send out on a particular day. When you set up the reminder we get your local time zone from your device (computer, phone, etc.) so if it is not set properly or that information is not available, the reminders may be a little later or earlier.
Also, if you change time zones after setting up the reminder they may come a little (or a lot) later or earlier, too. Then you have to figure in the delay caused by the delivery method. Most email is pretty fast and so are text messages but they can introduce a delay.
Can I change or edit a reminder?
No. Just cancel it and set up a new one.
Can I cancel a reminder?
Yes. When you first set it up we will send you an email or text message with a link that you need to follow to finalize the set up. This lets us know that you own the email address or phone number. If you don’t follow the link we send you, the reminders will be canceled. Once you have verified your email or phone number, you can cancel any remaining reminders after we send you the first one. There will be a link included in that message that will let you cancel any remaining reminders.
I didn’t get the email/text message to verify my reminders. What do I do?
Panic!! No, just kidding. It is possible that you entered your email or phone number wrong (someone else might be getting a weird message) or your mobile carrier lost it or blocked it (that wouldn’t surprise you, would it?) or the email went to that place where socks go. Just try again by setting up a new one.
There is no way to recover the code and we don’t let anyone see/search/find your email or phone number so it is lost forever. It’ll be deleted on the next trash day. The bits will be recycled into new, useful reminders.
How come I can’t set a reminder two days from now (or more than a year from now)?
If you need a reminder for two days from now you need more help than we can give you. You can set a reminder for any time between seven days from the present day to 13 months later – those are the rules. If you want a reminder two years from now, set up a reminder a year from now to set up the reminder – they’re cheap. If you would like it to work some different way, let us know. Maybe we’ll include your feature request in some future update.
Is my email address or phone number safe or will it be used for spam or sold or written on a bathroom wall?
Yes it is safe and no, it will not be used for spam, sold or written on any wall. We obviously have to save your email address or phone number in order to send you the reminder but that is all we do with it. Two weeks after the last reminder is sent the entire record is deleted from our database.
We will send you one email or text message to verify that you are who you say you are and finalize the set up of the reminder and then the reminders themselves (depending on how many you have asked for) and that is it.
We hate spam and try to protect ourselves from spam and we think it is only fair to do the same for you. This is for fun and spam isn’t any fun. You can read about what data we collect and how we protect it on our site.
Does anyone write email addresses on bathroom walls? That sounds so old school and creepy all at the same time.
Okay, seriously, what data do you have about me and how do you use it?
There is a long and boring answer to this here. To summarize it, we get information that all web sites get while operating, we have a mail server that keeps a log for a little while and we store email addresses until we don’t need them to send reminders. The honest truth is that your data isn’t that interesting to us and we don’t have the time or the desire to look at it or keep it. Facebook will do that for you.
Unless we are compelled by some court to give up your data, we will never share it with anyone.
Why all the ads?
The Half Birthday Calculator and other date based tools we offer cost money to host and support but we offer them to you for free. To help pay for the site we host advertisements. We are careful to only allow certain kinds of advertisers and products but we want to know if you see an ad that offends you or you think is inappropriate. When you click an ad you see here you help us keep this service free.
Uh oh. You don’t see any ads?
You must have an ad blocker or have your browser set to block ads. We agree that ads can be annoying but our ads aren’t! They don’t make noise, flash in your face or get in the way. They just provide us with a few pennies that we use to keep this service up and running. You can allow ads for EventCalc.com and continue blocking ads from other sites.
Or, you can show your appreciation for having the awesome power of EventCalc available to you by buying us a few seconds of server time by Buying Us a Coffee. You will feel amazing for donating and we will be forever grateful. We won’t actually buy coffee – we’ll buy more server time. Thanks!