Next Birthday Calculator

What the next birthday calculator does

This one looks forward instead of back. Type in your birth date and it works out the date of your next birthday, how many days away it is, which birthday it will be, and how long it has been since you were born. So rather than telling you how old you are, it tells you how long until you tick over to the next number.

It is the tool for the countdown, the "how many sleeps until my birthday" question, with the bonus of telling you which milestone is on its way.

How to use it

1. Enter Date. Your date of birth.

Press Calculate and it shows your next birthday, the days remaining, the birthday number, and the time since your birth.

How it finds your next birthday

It uses Moment.js, a date library, to do the date work. It takes the month and day you were born and places them on the current year. If that date has already gone by this year, it rolls forward to next year, and that gives your next birthday. From there it counts the days between today and that date, works out which birthday it will be, and measures how long it has been since you were born. Only the month and day decide the birthday, so the year you were born just feeds the age and the birthday number.

Which birthday is coming up

Along with the date, the tool names the birthday number, and that is often the part people care about most. It is one thing to know your birthday is in 50 days, and another to be reminded it is your 30th, or your 18th, or your 50th. Those round numbers are the ones people plan around, the milestone birthdays that get the bigger celebration. The number is simply your completed years plus one, since on your next birthday you finish another year. So if you are 29 now, the tool tells you the 30th is the one coming up.

An example

Say you were born on 20 August 1995. The tool sets your next birthday to 20 August of the current year, and if that date has already passed, it moves to 20 August the following year. It then counts the days from today to that date, tells you it will be your 31st birthday, and shows how long it has been since you were born in years, months, and days. As the days tick by, the countdown shrinks each time you check.

Where it comes in handy

Mostly for the simple joy of counting down to your own birthday, or someone else's. It is handy when planning a party, since it tells you how much lead time you have. And it earns its keep around the milestone birthdays, the 18th, 21st, 30th, 40th, 50th, where knowing exactly how long you have got helps with booking and organising something bigger.

Questions people ask

When is my next birthday?

Enter your date of birth and the tool gives you the date of your next birthday, along with how many days away it is.

How many days until my birthday?

It counts the days from today to your next birthday, so the number shrinks each day as the date gets closer.

Which birthday will it be?

The tool tells you the birthday number, which is your completed years plus one. If you are 29 now, your next birthday is your 30th.

What if my birthday has already passed this year?

Then the tool rolls forward to next year and counts down to that date instead, so you always get the genuinely next one.

References

1. Moment.js, the JavaScript date library used to find the next birthday and count the days. https://momentjs.com/