Half birthday calculator

A half birthday falls six months after a birthday, or the point where someone is a whole number of years and six months old. Enter a date of birth to get the next one, the age at that moment and the countdown.

Type dates as YYYY-MM-DD, for example 1990-05-15.
Next half birthdaySun, Nov 15, 2026
Days to wait12 days
Age on that day
36 years 6 months
36 years 6 months
Sun, Nov 15, 2026
37 years 6 months
Mon, Nov 15, 2027
38 years 6 months
Wed, Nov 15, 2028
39 years 6 months
Thu, Nov 15, 2029
40 years 6 months
Fri, Nov 15, 2030

Runs in your browser: nothing you enter is sent anywhere.

How to use it

  1. Enter the date of birth as YYYY-MM-DD.
  2. The second date is the day to search from. Change it to look ahead or back.
  3. Read the next half birthday, the days to wait and the age on that day. The list below shows the following five.

How it works

The half birthday after k whole years is the date of birth moved forward by 12 × k + 6 calendar months. The first of these on or after the search date is the answer. When the day of the month does not exist in the target month, the month’s last day is used.

Worked example

Born on 15 May 1990, searching from 3 November 2026: the 36th year and six months ends on Sunday, 15 November 2026. That is 12 days after 3 November, and the person is then 36 years and 6 months old.

Ideas

  • Celebrate children’s half birthdays, which are popular for those born near a holiday.
  • Use it for pets, when the exact birthday is known.
  • For the exact age on any day, use the age calculator.

Frequently asked questions

How is a half birthday calculated?

It is the date of birth plus 6 months plus any number of whole years. Someone born on 15 May has half birthdays on 15 November, in every year.

What if the birthday is on the 31st or on 29 February?

When the target month is shorter, the last day of that month is used. A birth date of 31 August gives 28 February, or 29 February in a leap year.

Is today counted if it is my half birthday?

Yes. The search starts on the date you enter and includes it, so the countdown shows 0 days on the day itself.

Does a half birthday mean 182 or 183 days?

No. The calculator adds six calendar months, so the number of days varies between 181 and 184 depending on the months passed.

More in Date & time

All tools in this category: Date & time ·Updated November 3, 2026

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