# When is my half birthday?

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.

- Page: https://www.acalculator.org/days/half-birthday-calculator
- JSON spec: https://www.acalculator.org/days/half-birthday-calculator.json
- Version: 53058eb05e76

## Default answer

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.

## Inputs

| Key | Label | Description |
| --- | --- | --- |
| birth | Date of birth | Your birthday, with the year you were born. |
| on | Count from | The date to count from. Today, unless you change it. |

## Outputs

| Key | Label | Description |
| --- | --- | --- |
| next | Next half birthday | The first half birthday on or after the count-from date, with its weekday. |
| days | Days until your half birthday | Days from the count-from date to the next half birthday; 0 when it is that day. |
| countdown | Countdown | The days to the next half birthday in words: “today”, “1 day to go”, or “N days to go”. |
| turning | Age on that half birthday | The age in years on the next half birthday, a whole number and a half. |
| every | Half birthday each year | The month and day of the half birthday: six months after the birthday. |
| first | First half birthday | The date you turned six months old. |

## 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.

## Assumptions

- 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.

## Worked examples

1. birth = 1995-06-15, on = 2026-10-02 gives next = 2026-12-15, days = 74, turning = 31.5, every = December 15, first = 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. birth = 2001-08-31, on = 2027-01-10 gives next = 2027-02-28, days = 49, turning = 25.5, every = February 28 (February 29 in leap years).
3. birth = 2001-08-31, on = 2028-01-10 gives next = 2028-02-29, turning = 26.5.
4. birth = 2000-02-29, on = 2026-03-01 gives next = 2026-08-29, every = August 29, countdown = 181 days to go.
5. birth = 2010-03-31, on = 2026-09-30 gives next = 2026-09-30, days = 0, countdown = today, turning = 16.5, every = September 30.

## FAQ

### 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.

## Sources

- The Python Standard Library, datetime: Basic date and time types (proleptic Gregorian calendar; date differences in days), used to check the worked examples, retrieved 2026-10-02. https://docs.python.org/3/library/datetime.html