EventCalc – FAQs

The following FAQ is a copy of the one you can read at EventCalc.com.

The Half Birthday Calculator

What is a half birthday and why do I care?

A “half birthday” is when you are halfway between actual birthdays. 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!

Can’t I just add 6 months to get my half birthday date?

Well, you could (and most other half birthday “calculators” do just that) but it is likely that you would be celebrating on the wrong day – basically living a lie. Why? Months have different numbers of days in them (think February with 28 or 29 days depending on the year). And have you noticed that there are fewer days in the first six months than there are in the last six months?

The variable number of days in each month, the fact that there are more days in the second half of the year, and the variability of leap years makes the calculation much more difficult – and interesting – than just adding six months.

Some half birthdays ARE six months away from the actual birthday but many are not – and you want to do it right, don’t you? For example, half a year after January 1st, 2001 is July 2nd.

Hold on, can adding six months really be all that inaccurate?

Yes. In years before a leap year, adding six months will lead to the wrong date more than two thirds of the time. In leap years and years that don’t have a leap year following them, adding six months will be wrong more than 84% of the time. Here is a chart showing the error distribution. The top bar is a year before a leap year (1999 is a good example), the second bar is for a leap year (2000) and the third bar is for a year not preceding a leap year.nerdy chart - you should load it

The light blue bar (right end) represents dates that will be correct when adding six months. The rest are one or more days off (the orange is when the month will be wrong!).

You probably won’t get very far in life if you show up on the wrong day more than 75% of the time. Yes, this is “just” your half birthday but knowing you are right is better than just faking it. Most people know their actual birthday so why not your actual half birthday?

Is the calculator really accurate?

Yes. If you think it isn’t let us know why. We use time-tested algorithms to make the calculations and have been at this since 2006. We’ve looked at this a lot harder than most people.

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. In theory, at the stroke of midnight the two agree on the number of days – but only for a second. (We have not actually seen this – 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 doesn’t matter for most uses. For example, driver’s licenses don’t have a time of birth on them. So 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 challenging and 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 occasionally and are not consistent around the world. Some years, countries and states skip them altogether. This makes it very complicated.
  • How many leap-seconds have there been since you were born? They add or subtract seconds every now and then (there is no set schedule) based on astronomical observations. So how do you account for those seconds?
  • Do you know what time you were born – really? Was the clock they consulted accurate? Did the person recording the time do it at first breath, cutting of the cord, crowning? Did they write it down correctly?

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 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 in the calendar (so, February 28th).

If you want to count from the 28th, 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.)

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 the day 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.

Got that?

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”. You have to know more Latin than we do to make sense of the naming convention – we only know what we read.

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?

Where are the ads? Are you crazy?

Yeah, we’re crazy. Actually, the proliferation of ads and BS that some sites call “content” drives us crazy. At one point The Half Birthday Calculator had ads. Those ads helped to pay for things like servers and connection fees. Ads fund a lot of services (and line people’s pockets) but they have gotten too invasive and the games people play to attract clicks have gotten ridiculous. Companies tracking your every move on the web, selling your data, making you an unwitting and maybe unwilling participant isn’t a great look. We don’t want to play that game. You are probably here for fun and we provide this service for fun – there should be no strings attached and Google and Meta should not profit off of your data. We turned off all activity tracking for the same reason. You are not leaving any footprints when you visit EventCalc. Be free!!

Wow, that turned into a rant. Sorry.

No ads also means that we don’t make any money when people use the site and we pay for servers, development, and maintenance ourselves.

If you enjoy what we have to offer and want to help pay the bills in a small way you can buy us a coffee. Or, you could donate to your local food bank or other charitable organization – tell them EventCalc sent you if you want to confuse them. If you do any of that, please let us know so we can enjoy the moment with you.

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. (There is a lot more information in the Half Birthday Calculator section for more incredibly boring information about this.)

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.

Count Down/Up

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 optionally give it a title so you know what you are looking at.

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.

Be aware that if you change timezones between when you set it up and when you access it again, the countdown will be wrong by the difference between the original and new time zones. Get around this by just setting up a new one – they are free, go for it.

Is there any limit to the number of countdowns I can have?

No. You are on your own if you want to keep track of a bunch of links. Or just set up a new one. Again, they are free so knock yourself out.


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 will verify that you are actually requesting the reminder. This lets us know that you own the email address or phone number. If you don’t verify a reminder we will cancel it. 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. The entire record is deleted from our database within two weeks of the last reminder (we have slow trash service).

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. So you should expect at least two emails from us but not more than four. All of our emails come from reminders@eventcalc.com (and we don’t receive anything sent to that address).

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. If you have any questions about how we handle your data, please send us an email. Or, look below at the General Questions (you’ve come this far, why not?).

Does anyone write email addresses on bathroom walls? That sounds so old school and creepy all at the same time.

What if I don’t ever want to hear from EventCalc again?

That’s cool – we wish we could turn off emails being sent to us all the time. You can put yourself on our “Never Contact” list and we will never contact you. In fact, if you want to hear from us again after adding yourself to the “Never Contact’ list you have to send us an email so we can remove you. There is no way to do this yourself.

General Questions

Okay, seriously, what data do you have about me and how do you use it?

EventCalc, like all web services or pages, is given your IP address and some other information so that the requested page or information can be sent back to you. In the case of EventCalc, this includes a session ID that we use to keep track of where you are in the app and what it is that you have asked us to do. The ID is kept for as long as you are active on the site plus about a day. The session ID is stored on your device as a cookie. You can see our cookie (called ‘eventcalc3’) and see that all it holds is the session ID. Once you leave the site the cookie expires immediately or when your browser is configured to delete it.

If you ask us to send you a reminder, we save your email address or phone number so we can send you the reminder(s). Once we are done sending those, we delete all of your data within a week (garbage day is once a week so it could take as long as 7 days). After that, there is no record of you or your reminder in our database. We don’t record your information for any other reason. We also don’t use any tracking services (Google, Meta, etc.) so your visit to EventCalc is essentially between us, your ISP and you. If you would like to see exactly what we get when you visit, let us know and we’ll send you a sample of what our server logs look like.

Do you have any other websites I can waste time on?

We have a number of other websites but none of them are for general time wasting (read: boring) and most of them actually cost money to use and are not for the general public.

Remember if you want to help support the “critical mission” of this website you can buy us a coffee. Or, you could donate to your local food bank or other charitable organization in the name of EventCalc. That’ll make ’em wonder. We all need a little wonder in our lives. (If you do that, please let us know so we can bask in the wonder, too.)

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