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- Your half birthday is the date exactly six months after your birthday.
- Enter a date of birth to see the next one, the age you will turn and the days left.
- If that day does not exist six months later (August 31 gives the end of February), the last day of that month is used.
- The tool also lists your next five half birthdays and your next full birthday.
How to use the half birthday calculator
Enter the date of birth
Type or pick the birth date of yourself, your child or anyone else.
Read the next half birthday
The headline shows the date, the weekday and the age being reached, for example 36½.
Check the countdown
See how many days are left and when the next full birthday is.
Plan ahead
Use the list of the next five half birthdays to add them to your calendar.
How a half birthday is calculated
A half birthday is found by moving six calendar months forward from the birthday while keeping the day of the month. The calculator uses whole months, not 182 or 183 days, so the date always matches the same day number.
Half birthday formula
Month = birth month + 6, wrapping around after December
Day = birth day, or the last day of the month if that month is shorter
Age = whole years since birth + ½
People born from January to June have their half birthday later in the same calendar year. People born from July to December have it early in the next year.
Half birthday examples
Example 1: a spring birthday
Born March 15, 1990, counting from November 7, 2026.
- Next half birthday Wednesday, September 15, 2027
- Turning 37½
- Days left 312
- Next full birthday March 15, 2027 (in 128 days)
The 2026 half birthday on September 15 has already passed, so the next one is in 2027.
Example 2: a short month
Born August 31, 1990, counting from November 7, 2026.
- Next half birthday Sunday, February 28, 2027
- Turning 36½
- Days left 113
- Next full birthday August 31, 2027 (in 297 days)
February has no 31st, so the last day of the month is used. In a leap year that day is February 29.
Example 3: the day is today
Born May 7, 1990, counting from November 7, 2026.
- Next half birthday Saturday, November 7, 2026
- Turning 36½
- Next full birthday May 7, 2027 (in 181 days)
When the half birthday is today, the result simply says Today!
Birth month and half birthday month
Each half birthday falls six months later, on the same day number.
- January July
- February August
- March September
- April October
- May November
- June December
- July January
- August February
- September March
- October April
- November May
- December June
Days 29, 30 and 31 move to the last day of a shorter month.
Where a half birthday calculator helps
Plan a small celebration
Pick the right date for a half birthday party, a treat or a family dinner.
Mark a baby milestone
Many parents celebrate the six-month mark, and a half birthday keeps the same date every year.
Send a card or gift
Know the date and the age in advance so a message arrives on time.
Add it to your calendar
Copy the next five dates into a calendar and set a reminder.
A half birthday is a tradition, not an official date. For an exact age in years, months and days, use the Age Calculator. For the Korean way of counting age, see the Korean Age Calculator.
Half birthday calculator FAQ
What is a half birthday?
It is the date six months after your birthday. Some families and classrooms celebrate it, especially for children with summer birthdays.
How do I calculate my half birthday?
Add six months to your birth date and keep the day number. Born on March 15, your half birthday is September 15. Born on September 15, it is March 15.
What is the half birthday for August 31?
It is the last day of February, which is February 28 in most years and February 29 in leap years.
What if I was born on February 29?
Your half birthday is August 29. Your full birthday is shown as February 28 in years without a leap day.
Is a half birthday 182 or 183 days after the birthday?
Not in this calculator. It uses six calendar months, so the date always has the same day number. Counting 182.5 days can land a day or two earlier or later.
How old am I on my half birthday?
You are your age in whole years plus one half, for example 36½. A baby reaching six months is 0½.