Half Birthday Calculator is a free, independent website that tells you the exact date of your half birthday and explains how half birthdays work, from the month-end rule to leap years. Everything here is written and maintained by the Half Birthday Calculator Team.
What you can do here
- Find your half birthday in seconds. Enter a date of birth and the calculator shows your next half birthday, the day of the week, how many days are left and how old you will be.
- Understand the rules. Our method page explains exactly how the date is worked out, including birthdays on the 29th, 30th and 31st and on 29 February.
- Plan the day. Our guides cover what a half birthday is, ideas to celebrate, gifts, cakes, a baby’s halfway to one milestone and half birthday twins.
- Look up any date. The half birthday chart lists the half birthday for every date of the year, and our 6 months from today, months to years and age calculators handle the date maths around it.
- Use it in your language. The calculator is available in English, German, Spanish, French, Russian and Portuguese.
Why this site exists
A half birthday sounds simple: six months after your birthday. In practice people get stuck on the details. What happens if you were born on 31 August, when February has no 31st? Is a half birthday six calendar months later, or exactly 182 days later? What about people born on 29 February?
Many date tools answer these questions differently or not at all. We built this site to give one clear, consistent answer, to explain the rule behind it, and to keep the guides around it practical and easy to read.
How we keep the dates accurate
- One published rule. The calculator follows the calendar method described on our method page: same day, six months later, moved to the last day of the month when that day does not exist.
- Tested examples. Before a change goes live, we check the calculator against dates that hit every rule, including the end of each month, 29 February and the change of year.
- Reliable sources for everything else. Where a guide touches on health or child development, such as baby milestones at six months, we follow official public guidance and link to it. Those guides are general information, not medical advice.
- Dated updates. Guides show when they were last updated, and we revise them when rules, guidance or reader questions change.
Read our full editorial policy for how we research, write, review and correct content.
Your privacy
The calculator runs in your browser. The date of birth you enter is used only to work out the result on your screen; it is not stored or sent to us. See our privacy policy for details about cookies and analytics on the rest of the site.
How the site is funded
The calculator and guides are free to use. The site may show advertising, which helps pay for hosting and new content. Advertisers do not choose, review or influence what we write, and we do not publish paid or sponsored articles.
Who maintains the site
The site is run by the Half Birthday Calculator Team, an independent team that writes the guides, maintains the calculator and answers reader messages. We are not affiliated with any event, party-supply or gift company.
Get in touch
Found a date that looks wrong, or have a question we have not answered? Contact us and we will look into it. Corrections are always welcome.
Last updated: 4 November 2026.