About the Half Birthday Calculator
A half birthday falls six months after your birthday. For a child, being "seven and a half" is an achievement worth announcing; for adults, a half birthday is a fun excuse for a small celebration. Half birthdays are especially popular with people whose real birthday is awkward — close to Christmas or New Year, in the middle of the summer holidays when school friends are away, or on 29 February, which only comes round once every four years.
This half birthday calculator finds your half birthday date, counts the days until it arrives, tells you the age you will be, and also shows the exact midpoint between two birthdays by day count, which is not always the same date. It handles birthdays at the end of a month correctly, moving the half birthday to the last day of a shorter month when needed.
How to Use the Half Birthday Calculator
Enter your date of birth.
Optionally, enter a date to count from. Leave it blank to count from today.
Your next half birthday and the countdown appear below.
How the Half Birthday Is Found
half birthday = birthday + 6 calendar months
15 May → 15 November
3 January → 3 July
31 August → 28 February (29 February in a leap year)
29 February → 29 AugustAdding calendar months keeps the same day of the month whenever it exists. When it does not — there is no 30th or 31st of February — the half birthday moves to the last day of that month.
Step-by-Step Example
Born 15 May 1990, counting from 29 September 2026.
Birthday this year: 15 May 2026
Plus 6 months: 15 November 2026
Days from 29 September to 15 November = 47
Age then: 36½The half birthday is Sunday 15 November 2026, 47 days away.
The Exact Midpoint
Six calendar months is not exactly half a year. From 15 May to 15 November is 184 days, while from 15 November to the next 15 May is 181 days. The exact midpoint, half of the 365 days between birthdays, is 182.5 days after 15 May — noon on 13 November. For most people the difference of a day or two does not matter, but the calculator shows both so you can choose. The midpoint moves by half a day when a 29 February falls between the two birthdays, because the year then has 366 days.
Month-End Birthdays
Someone born on 31 August has no 31 February six months later, so the half birthday becomes 28 February, or 29 February in a leap year. Birthdays on 29 and 30 August do the same in common years. Birthdays on 31 March, May, October and December have half birthdays on 30 September, 30 November, 30 April and 30 June respectively, because those months have only 30 days. This end-of-month rule is the same one used by banks and spreadsheets when adding months to a date.
Leap-Day Babies
People born on 29 February face the opposite problem: their real birthday exists only in leap years, but their half birthday, 29 August, happens every year. Many leap-day babies make a point of celebrating the half birthday, and some jokingly count their age in real birthdays — a person born in 2000 had only their sixth true birthday in 2024.
Ideas for Celebrating
Half birthday traditions are informal. A half cake — literally a round cake cut in half — is a favourite. Some families serve half portions or celebrate with a half-sized party. At school, children with summer birthdays often mark their half birthday in class so they are not left out of the birthday celebrations their classmates enjoy during term time. For adults, a half birthday can be a quiet mid-year check-in on resolutions or goals.
Half Birthdays for Babies and Children
For babies, six months is a real milestone: many start solid foods and sit up around this age, and paediatric check-ups are often scheduled at six months. Parents sometimes mark each month with a photo; the half birthday is a natural halfway point before the first birthday. For young children, half years matter because a year is a large part of their life, and "and a half" makes the next birthday feel closer.
Understanding Your Result
The headline is the date of your next half birthday.
The countdown line gives the days to go, or wishes you a happy half birthday today.
The age line gives the age you will be.
The exact midpoint line gives the true halfway point between birthdays by day count.
When Should You Use This Calculator?
Use it to plan a half birthday party or classroom celebration.
Use it when your real birthday falls at an inconvenient time of year.
Use it to track a baby's six-month milestone.
Use it for fun, to see how close your half birthday is.
Common Mistakes
Adding 182 days instead of six months. The calendar date may differ by a day or two.
Forgetting month-end rules. 31 August plus six months is the end of February.
Counting from the wrong year. If this year's half birthday has passed, the next one is next year.
Assuming leap-day babies have no half birthday. 29 August exists every year, so they can celebrate it annually.
Mixing up day and month. Enter the date of birth in the year-month-day format, so that 5 June is not read as 6 May.