acalculator

When is my half birthday?

Type your date of birth. The half birthday calculator shows your half birthday, six months after your birthday, the date of the next one, how many days are left, and the age you turn, such as 31½.

Your numbers

Count from another date
Next half birthday
Tuesday, December 15, 2026

Your next half birthday is Tuesday, December 15, 2026, 74 days to go, when you turn 31.5.

Days until your half birthday
74
Countdown
74 days to go
Age on that half birthday
31.5
Half birthday each year
December 15
First half birthday
Friday, December 15, 1995

Answer for the example date Friday, October 2, 2026. It changes to today's date when the page loads.

Next half birthday: Tuesday, December 15, 2026. Your next half birthday is Tuesday, December 15, 2026, 74 days to go, when you turn 31.5.

How to calculate

Finds your half birthday, six months after your birthday, the date of the next one, the days until it, and the age you turn, such as 30½.

Example with the default inputs (Date of birth June 15, 1995, Count from October 2, 2026) on the example date Friday, October 2, 2026: Your next half birthday is Tuesday, December 15, 2026, 74 days to go, when you turn 31.5.

Method: Half birthday = birthday + 6 calendar months (the same day, or the last day of the month when that month is shorter); the next one is the first such date on or after the count-from date.

  • A half birthday is six calendar months after the birthday, not 182 or 183 days.
  • When the month six months later is shorter (August 31 to February), the half birthday is that month’s last day.
  • Each half birthday is counted from the date of birth, so August 31 gives February 29 in leap years and February 28 otherwise.

Machine-readable copies: Markdown, JSON.

Worked examples

Each example is checked against the calculator on every build.

  1. Date of birth 1995-06-15, Count from 2026-10-02 gives Next half birthday 2026-12-15, Days until your half birthday 74, Age on that half birthday 31.5, Half birthday each year December 15, First half birthday 1995-12-15.Source: The Python Standard Library, datetime (Gregorian calendar day counts), https://docs.python.org/3/library/datetime.html, retrieved 2026-10-02: date(2026, 12, 15) − date(2026, 10, 2) = 74 days
  2. Date of birth 2001-08-31, Count from 2027-01-10 gives Next half birthday 2027-02-28, Days until your half birthday 49, Age on that half birthday 25.5, Half birthday each year February 28 (February 29 in leap years).
  3. Date of birth 2001-08-31, Count from 2028-01-10 gives Next half birthday 2028-02-29, Age on that half birthday 26.5.
  4. Date of birth 2000-02-29, Count from 2026-03-01 gives Next half birthday 2026-08-29, Half birthday each year August 29, Countdown 181 days to go.
  5. Date of birth 2010-03-31, Count from 2026-09-30 gives Next half birthday 2026-09-30, Days until your half birthday 0, Countdown today, Age on that half birthday 16.5, Half birthday each year September 30.

How it works

Your half birthday is your birthday plus six calendar months:

  • The month moves forward six months (June to December, December to June) and the day stays the same.
  • When that month is shorter than the day (a birthday on August 29, 30 or 31, March 31, May 31, October 31 or December 31), the half birthday is the last day of that month. February has 29 days in a leap year (a year divisible by 4, except century years not divisible by 400) and 28 otherwise.
  • Half birthday k (k = 0, 1, 2, …) is 12k + 6 months after the date of birth, always counted from the date of birth itself. So an August 31 birthday gives February 29 in a leap year and February 28 in other years.

From the count-from date (today, unless you change it), the calculator finds the first half birthday on or after it, and shows:

  • Next half birthday: that date.
  • Days until your half birthday: the days from the count-from date to it, 0 when it is that day.
  • Countdown: today for 0 days, 1 day to go for 1, and N days to go otherwise.
  • Age on that half birthday: k + ½ for half birthday k (shown as 31.5 for 31½).
  • Half birthday each year: the month and day, such as December 15. For a birthday on August 29 it is February 29 (February 28 in common years), and for August 30 or 31 February 28 (February 29 in leap years).
  • First half birthday: the date you turned six months old (k = 0).

Dates run from 1600 to 2400 in the Gregorian calendar. A date of birth after the count-from date has no answer: "The date of birth is after the count-from date."

Worked examples by hand

Born June 15, 1995, counting from October 2, 2026. June + 6 months is December, so the half birthday is December 15. October 2 to December 15, 2026 is 29 + 30 + 15 = 74 days, and you turn 31½. The first half birthday was December 15, 1995.

Born August 31, 2001, counting from January 10, 2027. August + 6 months is February, which has 28 days in 2027, so the half birthday is February 28, 2027, 49 days away; you turn 25½.

The same birthday, counting from January 10, 2028. 2028 is a leap year, so the half birthday is February 29, 2028; you turn 26½.

Born February 29, 2000, counting from March 1, 2026. February + 6 months is August 29: August 29, 2026, 181 days to go.

Born March 31, 2010, counting from September 30, 2026. September has 30 days, so the half birthday is September 30: today, and you turn 16½.

Other questions people ask

How do I find my half birthday?

Add six months to your birthday and keep the day. A June 15 birthday has its half birthday on December 15; a January 4 birthday, on July 4.

What if my birthday is August 29, 30, or 31?

February has no 30th or 31st, so the half birthday falls on the last day of February: February 28, or February 29 in a leap year. An August 29 birthday gets February 29 in leap years and February 28 otherwise.

What about other month ends, such as March 31?

The same rule: September has 30 days, so a March 31 birthday has its half birthday on September 30. October 31 gives April 30, and December 31 gives June 30.

Is a half birthday 182 days after my birthday?

Not on this page. It counts six calendar months, so the gap is 181 to 184 days depending on the months between. Some people count half a year as 182 or 183 days instead, which can land a day or two away.

Why celebrate a half birthday?

Children with birthdays in the summer holidays or near Christmas often get a half birthday at school instead. Families also mark a baby’s first half birthday at six months old.

How old am I on my half birthday?

Your age then is a whole number and a half. Born June 15, 1995, you turn 31½ on December 15, 2026.