Half Birthday Calculator
Enter your birthday to find your half birthday: the date exactly six months from the day you were born.
How to calculate half birthday
Add six months to your birth month, wrapping past December into the next year, and keep the same day of the month. If the target month is shorter than your birth day (for example a 31st landing in a 30-day month), the date is clamped to the last day of that month.
Half birthday = birth month and day + 6 calendar months
Worked example
A birthday on 23 June.
- Add six months to June: December
- Keep the same day: the 23rd
- Count the days from 23 June to 23 December: 183
Result: Half birthday on December 23, 183 days after the birthday
Frequently asked questions
What is a half birthday?
A half birthday is the date exactly six months from your birthday. People use it to celebrate kids whose birthdays fall in school holidays, or just for a fun midpoint between birthdays.
How do I calculate my half birthday?
Add six months to your birth month and keep the same day. A birthday on 23 June gives a half birthday on 23 December. This calculator does the wrapping and month-length clamping for you.
Is a half birthday always 182 or 183 days away?
Roughly. Because months vary in length, the gap between a birthday and its half birthday is usually 181 to 184 days depending on which half of the year it spans.
What if I was born on the 31st?
If the month six months later has fewer days, the half birthday is clamped to the last day of that month. For example, 31 August maps to 28 February (or 29 in a leap year).