Days Until Birthday Calculator
Enter your date of birth to see exactly how many days remain until your next birthday. The calculator also shows your upcoming birthday date and your current age. All calculations run locally in your browser.
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How it works
The calculator uses JavaScript's built-in Date object to find the difference between your date of birth and today. It counts complete years first, then remaining months, then remaining days, correctly handling leap years and months of different lengths. Total days are the number of calendar days between the two dates.
Processing runs in your browser
All calculations are pure JavaScript running in your browser tab. Your date of birth is not sent to our servers, stored, or logged at any point.
Related operations
To work out days between any two dates, use the date calculator. For converting between Unix timestamps and human dates, try Unix timestamp. To convert times across zones, see the timezone converter.
Frequently asked questions
- How is the days until birthday calculated?
- The calculator sets this year's birthday date. If that date has already passed, it moves to next year's birthday. The difference between today and that date is the countdown.
- What if my birthday is today?
- If today is your birthday, the result reads "Happy birthday!" instead of a day count, and the Next birthday field shows "Today!".
- What if I was born on 29 February (leap day)?
- Leap day birthdays are handled correctly. In non-leap years, the calculator uses 28 February as the nearest equivalent birthday date.
- Is my date of birth stored anywhere?
- All processing runs in your browser. Your date of birth is not stored and is not sent to our servers.
Last reviewed September 30, 2026
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