The term half day as two words is correct and is a noun that refers to half a day. E.g., “He worked a half day today because it is his birthday.” Also, the hyphenated one-word term half-day is correct as an adjective. E.g., “He worked a half-day shift today.”
There are two correct spelling versions of the term half day.
The non-hyphenated version, half day, is a noun that refers to half of an entire day. You often use this term to describe working patterns or the amount of time something will take.
- I asked for a half day off work next week so that I can go to the dentist.
In contrast, the compound word half-day is an adjective. That means it goes before another noun to describe that the noun will last half a day or that something occurs at the midway point of a day.
- I avoid caffeine in my half-day drink because otherwise, I have problems sleeping.
Furthermore, in writing that follows AP Style, you should use the above rule concerning the adjective and noun forms of half day.
In addition, the rule mentioned above is a standard grammar rule that does not vary between the UK and the US.
Making a mistake with compound words is easy, and even many native speakers are guilty of it. Therefore, you should read the rest of the page to discover more about the different forms of half day.
Half Day
The two-word term half day is correct as the noun form. Therefore, you can use it to refer directly to a period of half a day.
The most common times you use the term is when you talk about work, school, or any other scheduled activity that usually takes all day.
- We are doing a half day today because of our overtime last week.
As well as using the term to refer to a single half day, you can also refer to a plural number of half days.
- Since Maria had her baby, she has been working half days.
Half-Day
The term half-day is a compound adjective that you can use to describe nouns. When you use the hyphenated version of the term, the noun must always come directly after half-day.
The most common use for the term half-day is to refer to work or study periods, but you can also use it to describe things you either do or consume at a half-day point.
As shown in these examples:
- He worked a half-day shift today because he felt sick.
- He likes to have a half-day nap before returning to work in the afternoon.
Halfday
The term halfday as one word without a hyphen is incorrect, and you should avoid it at all costs.
Instead, there are two ways in which you can write the term correctly.
The first is as two words with no hyphen, in which case half day is a noun.
- Correct: I am going to the office for a half day tomorrow.
- Incorrect: I am going to the office for a halfday tomorrow.
The second way to write the term is with a hyphen, in which case half-day is a compound adjective, and the noun it describes comes straight afterward.
- Correct: She is taking a half-day first aid course.
- Incorrect: She is taking a halfday first aid course.