Half Birthday Calculator
A half birthday is six months after a birthday. Enter the birthday to see the date, this year's weekday and the days to go.
Sources: Wikipedia Updated
Enter a birthday to see the half birthday
How a half birthday is worked out
Move forward six calendar months and keep the day of the month. If that day does not exist in the target month, use the month's last day.
The other method, described in the Wikipedia article on half birthdays, adds half a year in days instead. The calculator shows both, and the days between dates calculator counts the days between any birthday and its half birthday.
How to work out a half birthday: a worked example
A birthday on June 20:
- Six months after June is December.
- Keep the day: December 20.
- For comparison, the exact midpoint between June 20 and the next June 20 is 182 days later in a 365-day year, which is December 19.
For the countdown to the birthday itself, with the weekday and the age you turn, use the birthday countdown.
Half birthday for every month
| Birthday in | Half birthday in | Watch out for |
|---|---|---|
| January | July | |
| February | August | |
| March | September | March 31 becomes September 30 |
| April | October | |
| May | November | May 31 becomes November 30 |
| June | December | |
| July | January | |
| August | February | August 29, 30 and 31 become the last day of February |
| September | March | |
| October | April | October 31 becomes April 30 |
| November | May | |
| December | June | December 31 becomes June 30 |
Questions about half birthdays
When is my half birthday?
Six calendar months after your birthday, on the same day of the month. A birthday on March 15 has its half birthday on September 15. Enter your birthday above for the exact date and weekday this year, or count six months from any date with the days from today calculator.
What if the date does not exist six months later?
Then the half birthday is the last day of that month. A birthday on August 31 has its half birthday on February 28, or February 29 in a leap year, because February has no 31st.
Is six months later the same as halfway between two birthdays?
Not always. Six months can be anything from 181 to 184 days, while the true midpoint of a 365-day year is 182 or 183 days after the birthday, so the two can differ by a day or two.
The calculator gives the six-month date, which is the usual convention, and also tells you the exact midpoint.
What is a half birthday used for?
Mostly for celebrating summer-holiday or Christmas-time birthdays at a quieter time of year, and for ages stated in halves, such as school or sports cut-off dates.
Sources
- Wikipedia: Half-birthday — the two ways to calculate a half birthday (checked October 16, 2026)