Birthday Countdown
Enter a birthday to see the days, hours, minutes, and seconds until the next birthday, plus the age you'll turn. The result is reflected in the URL, so you can share the link as-is. Everything runs in your browser, so the date you enter is never sent anywhere.
The birthday you enter is processed only in your browser and never sent anywhere. The share link simply puts the date into this device's URL — nothing is stored on a server.
Enter a birthday and press "Calculate".
Happy Birthday!
Turning:
- Next birthday
- Turning
Time remaining
- d
- h
- m
- s
How to use
- Enter a birthday (include the birth year to also see the age you'll be turning).
- Press "Calculate" to see the days, hours, minutes, and seconds left until the next birthday.
- Press "Copy share link" to copy a URL that reproduces the same result.
How it works
How the next birthday is determined
We find the next date on which the month and day of the birthday you entered occurs. If this year's occurrence hasn't happened yet, it's used; otherwise, next year's occurrence is used. If today is exactly the birthday, we show "Happy Birthday!" and the remaining time is 0.
Age turned
The displayed age is the next birthday's year minus the entered birth year.
People born on February 29
If the upcoming year isn't a leap year, February 29 doesn't exist, so the date is rounded up to February 28. If the upcoming year is a leap year, February 29 is used as-is.
Breakdown of remaining time
The remaining time is the difference until midnight UTC on the next birthday, split into days, hours, minutes, and seconds. The seconds display updates automatically every second.
About the share link
Once calculated, the birthday you entered is reflected in the page URL (?date=birthday). Sending this URL lets the recipient's browser redo the same calculation from the same birthday and see the same result. The birthday is never stored on a server or sent to any third party.
Supported range
Birth years from 1 to 9999 CE are supported. Entering a year outside this range, or a year later than the current year, results in an error.
About data transmission
All calculations happen entirely inside your browser. The birthday you enter, along with everything else, is never sent to any server.
FAQ
Is the birthday I enter sent anywhere?
No. All calculations happen entirely in your browser, and no data is ever sent to any external server or API. The share link is just the birthday added to this device's URL — it isn't stored anywhere.
What is the share link? If I send it to someone, will they learn whose birthday it is?
After calculating, the birthday is reflected in the page URL as "?date=birthday", and the link works entirely within the recipient's own browser. It's recalculated locally on their device — nothing is stored on a server or sent to a third party. Only the person you send the link to will see whose birthday it is.
How is the next birthday calculated for someone born on February 29?
If the upcoming year is a leap year, February 29 is used as-is. If it isn't, February 29 doesn't exist, so February 28 is used instead.
Do I need to enter the birth year to use this?
Yes, since the date field captures a full year-month-day value. The year is used only to display the age you'll be turning on the next birthday; it doesn't affect any other calculation.
What happens if today is the birthday?
You'll see "Happy Birthday!" and the remaining time is treated as 0. The next birthday date shown will be today's date.
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