Enter a date of birth to find the half birthday, exactly 6 months after the birthday. You also get the weekday, the age you turn and how many days are left.
Born on the 31st: there is no 31 February, so the half birthday moves to the last day of February.
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This half birthday calculator is for parents, teachers, friends and anyone planning a half year celebration. It adds 6 months to a date of birth, handles short months correctly, and counts the days from today, or from any date you choose, to the next half birthday.
When Is My Half Birthday?
Your half birthday is 6 calendar months after your birthday, on the same day number. Someone born on 20 April has a half birthday on 20 October. If that day does not exist, it moves to the month’s last day, so a 31 August birthday gives 28 February, or 29 February in a leap year like 2028.
How Do You Calculate a Half Birthday?
Add exactly 6 calendar months to the birth date, keeping the same day of the month, and if that month is too short, use its last day instead.
if the day does not exist in that month, use the month’s last day
A half birthday is the day you are exactly half a year older than on your birthday. Counting by calendar months, not by 182 or 183 days, keeps the same day number, so 20 April becomes 20 October. This month end rule is the same one spreadsheet programs use when adding months, such as the EDATE function in Microsoft Excel, which returns the last valid day when the target month is shorter.
When Is the Half Birthday for Someone Born on August 31?
Someone born on 31 August has a half birthday on 28 February, or on 29 February in a leap year, because February never has 31 days.
A leap year adds 29 February every 4 years, with century years only counting when divisible by 400, under the Gregorian calendar rule. So a person born on 31 August 2010 had their first half birthday on 28 February 2011, has one on 28 February 2027, and gets 29 February in 2028. The same rule moves 31 March, 31 May, 31 October and 31 December birthdays to the 30th of the month six months later.
Half Birthday Date Table
Results from this tool for common birth dates:
| Birthday | Half birthday |
|---|---|
| 15 January | 15 July |
| 20 April | 20 October |
| 30 June | 30 December |
| 29 August | 28 February (29 in leap years) |
| 31 August | 28 February (29 in leap years) |
| 31 March | 30 September |
| 31 December | 30 June |
| 29 February | 29 August |
Why Do People Celebrate Half Birthdays?
People often celebrate half birthdays when the real birthday is hard to mark, such as a birthday on or near a big holiday like 25 December, or a summer birthday that falls when school is closed. Parents also mark a baby’s 6 month milestone this way. To see your exact age in years, months and days, use the age calculator, and to count the days to any other date, try the days between dates calculator.
Worked Example
Mia was born on 31 August 2010 and wants to plan her next half birthday from 10 October 2026. Enter the two dates. The tool shows Sunday, 28 February 2027, which is 141 days away, when she turns 16 and a half. It also notes that August 31 moves to the end of February. Counting from 10 October 2027 instead gives Tuesday, 29 February 2028, 142 days away, because 2028 is a leap year. For someone born on 20 April 1992 the next half birthday after 10 October 2026 is Tuesday, 20 October 2026, just 10 days away.
How Do You Use the Half Birthday Calculator?
Enter the date of birth
Pick the birth date. Any year from 1800 onwards works.
Check the count from date
It fills in today from your device. Change it to plan ahead.
Read the next half birthday
See the date and weekday of the next half birthday.
See the extra details
Check the days to go, the age you turn and the yearly half birthday date.
Frequently Asked Questions
Is a half birthday exactly 6 months or 182 days?
This tool uses 6 calendar months, so the day number stays the same, such as 15 January to 15 July. Counting 182 days would give a different date in most years, often off by one to three days.
What is the half birthday for 29 February?
Someone born on 29 February has a half birthday on 29 August every year. August always has 31 days, so the date never needs to move, even though the birthday itself only appears in leap years.
What is the half birthday for 31 December?
A 31 December birthday has a half birthday on 30 June, because June has only 30 days. The tool applies the month end rule and moves the date to the last day of the shorter month.
How many days until my half birthday?
Enter your birth date and the tool counts from today's date on your device. For a 31 August birthday, counting from 10 October 2026 gives 141 days to Sunday, 28 February 2027.
When is a baby's first half birthday?
A baby's first half birthday is 6 months after birth. A baby born on 1 October 2026 turns 6 months old on 1 April 2027, which the tool shows as the first half birthday and the age of 0 and a half.
Why does the count from date use my device?
The tool reads today's date from your phone or computer clock, so it never needs the internet. If your device date is wrong, or you want to plan ahead, simply type a different count from date.
Sources and Further Reading
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Last reviewed: October 2026