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Birthday Calculator
Enter a date of birth to count down to the next birthday and see the weekday it falls on and the age being reached. For fun, it also finds the next half birthday and the dates you turn 10,000 days and one billion seconds old.
- Next birthday
- Sat, May 15, 2027
- You will turn
- 37
- It falls on a
- Saturday
- Next half birthday
- Sun, Nov 15, 2026
- 10,000 days old on
- Sat, Sep 30, 2017
- One billion seconds old on
- Fri, Jan 21, 2022
Saved setups
Save a set of inputs you reuse — your usual rate, your loan, your room sizes — and load it back in one tap.
Your recent calculations
Results you calculate here are kept on this device so you can come back to them.
Formula
How to use it
- Enter the date of birth.
- Read the countdown and the weekday of the next birthday.
- Scroll the results for the milestone dates.
Worked examples
Born May 15, 1990, counted from October 11, 2026
- Days until your birthday
- 216 days
- Next birthday
- Sat, May 15, 2027
- You will turn
- 37
- It falls on a
- Saturday
- Next half birthday
- Sun, Nov 15, 2026
- 10,000 days old on
- Sat, Sep 30, 2017
Born February 29, 2004, counted from January 1, 2027
- Next birthday
- Sun, Feb 28, 2027
- You will turn
- 23
Milestones worth a party
10,000 days comes at about 27 years and 4½ months. One billion seconds arrives at roughly 31 years and 8 months. 20,000 days is around age 54¾. They are as arbitrary as any birthday — and a good excuse.
Questions people ask
When is my half birthday?
Six months after your birthday. For a May 15 birthday it is November 15.
When do leap-day babies celebrate?
In non-leap years most celebrate on February 28 or March 1. This calculator uses February 28.