Half Birthday Calculator
Half birthday calculator works out Next half birthday and Falls on a from Date of birth, Find the next half birthday after and Half a year means. The default figures on this page give next half birthday of 2027-07-15; change any entry and the result, the working and the sources update together.
Your figures
Updates as you typeHow this is worked out
3 steps
- Birthday in play: 2027-01-15.
- Adding six calendar months gives 2027-07-15.
- 2026-09-14 to 2027-07-15 is 304 days; the age reached is 7 and a half.
Its 4 worked examples are re-run on every release, last on 15 September 2026. What changed
Sources and references
2 sources
What the half birthday calculator calculates
The date half a year from a birthday, the weekday it falls on, and the days until it. The calendar reading adds six months and clamps a non-existent day to the month end (31 August gives 28 February, or 29 in a leap year); the alternative adds half the days of the year, 182 or 183. The half birthday reported is the next one on or after the reference date.
How to use this half birthday calculator
Enter Date of birth, Find the next half birthday after and Half a year means. Next half birthday updates as you type, and “Use a worked example” loads checked figures you can adjust. Change one figure at a time to see what drives the result.
How the result is worked out
Open “How this is worked out” beside the result for the step-by-step calculation behind Next half birthday, Falls on a and Days until.
The method follows ISO 8601-1:2019, Date and time - Representations for information interchange and TC39 Temporal proposal, PlainDate.add with the "constrain" overflow behaviour.
A January birthday, six months on example
With Date of birth: 2020-01-15, Find the next half birthday after: 2026-01-01, the calculator returns Next half birthday: 2026-07-15, Days until: 195, Whole years of age then: 6. This example is checked against an independent source in the test suite.
What you can compare
Change one input at a time to see how it affects Next half birthday, Falls on a and Days until. The inputs you can vary are Date of birth, Find the next half birthday after and Half a year means.
Results are general information, not financial, tax, legal, medical or engineering advice. Check any decision that matters with a qualified professional.
See something wrong? Report a problem with this calculator
Frequently asked questions
How do you calculate your half-birthday?
The date half a year from a birthday, the weekday it falls on, and the days until it. Open “How this is worked out” beside the result to see each step for your own figures.
Is your half-birthday 6 months after your birthday?
The date half a year from a birthday, the weekday it falls on, and the days until it. Put your own figures in above and the working updates beside the result. For scale, the default figures on this page give 2027-07-15.
If my birthday is February 15, when is my half-birthday?
It needs Date of birth, Find the next half birthday after and Half a year means. Nothing else is required, and the figures stay in your browser.
Is November 30th considered a half-birthday?
The result gives Next half birthday, Falls on a, Days until, Age then, Whole years of age then and Previous half birthday, each labelled with its unit so the figure can be read on its own.
What information do I need for the half birthday calculator?
You need Date of birth, Find the next half birthday after and Half a year means. The page opens with default figures that give next half birthday of 2027-07-15, so you can see the scale before entering your own.
What does this half birthday calculator show?
It shows Next half birthday, Falls on a, Days until, Age then, Whole years of age then, Previous half birthday, Birthday it follows and Method, with the working and any warnings for your entries.