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End-of-month birthdays
If six months later has no matching day (for example, August 31 → February), we use the last day of that month (February 28, or 29 in leap years).
How it is worked out
A half birthday is the same day of the month six months after your birthday. Born March 15, your half birthday is September 15. Because months have different lengths, the gap is 181 to 184 days rather than exactly 182.5. If the day does not exist six months later (August 31 becomes February), we use the last day of that month.
Why people celebrate it
Families often celebrate half birthdays for children born near the winter holidays or in the summer break, so the party can happen at school or away from Christmas. Some people also use it as a mid-year check-in. To count down to it, enter the date in the days until tool.
Related tools
- Days until any dateCountdown in days and weeks
- Date differenceDays between two dates
- Add or subtract daysFind a date N days away
- Age calculatorExact age in years, months, days
Frequently asked questions
When is the half birthday for May 15?
November 15.
When is the half birthday for February 29?
August 29, six months after February 29.
Is a half birthday exactly 182.5 days away?
No. It falls on the same day of the month six months later, which is 181 to 184 days depending on the months involved.