Half birthday calculator
A half birthday is six calendar months after your birthday. Born on 15 June, your half birthday is 15 December. Where the target month is shorter the date clamps; 31 August gives 28 or 29 February.
How to find your half birthday
Half birthdays exist mainly for children whose birthdays fall in the school holidays, so a celebration can happen with classmates. Some schools also use them for a mid-year acknowledgement. The six-calendar-month convention is more common than the 182-day one because it keeps the same day number, which is easier to remember and lands on a predictable date every year. It is also, strictly, not the halfway point. Six calendar months forward from 15 January is 181 days, while six months forward from 15 July is 184. The first half of the year is the short one, so a winter birthday’s half birthday arrives slightly early and a summer one’s slightly late. Three days either way is nobody’s problem, but it is why the two conventions cannot be made to agree. The neatest case is a 29 February birth date: six months on is 29 August, a date that exists every year, so a leapling gets an annual half birthday even in the years their real one is missing.
Questions
The date six calendar months after your birthday.
Six calendar months by convention, which keeps the same day number.
Not quite. Six months from 15 January is 181 days and six months from 15 July is 184, because the first half of the year is shorter.
It clamps to the end of a shorter target month: 31 August gives 28 or 29 February, and 31 March gives 30 September.
The half birthday is 29 August, which exists every year, so it lands annually even when the birthday itself does not.
Usually for children whose birthdays fall in school holidays, so they can celebrate with friends.
Only for a birth date at the very end of August, where the clamp lands on 28 February in a common year and 29 February in a leap one. Everything else is fixed.