- First of all, Grammar Book cautions us that when hyphens are used to indicate a range, as in 30-40 yards away, a space is never used around the hyphen. Nor is it acceptable to substitute in a dash, either en or em, instead.
2. However, if the range is in years or pages, you should use an en dash instead of a hyphen. Ex: 1776─1976, pp.18─27.
3. Compound numbers. Numbers from twenty-one to ninety-nine should be hyphenated. I looked this up several places because I’d seen it recommended otherwise for chapter headings, but the overwhelming majority of sites recommended this, including Chicago Manual of Style.
In the interest of being complete, I did find one site that recommended not hyphenating the same compound numbers when they followed the noun, instead of preceding it, but they were the only one.
4. Fractions should be hyphenated according to Grammar Monster. Ex: One-and-a-half, three-quarters, and six-and-seven-eighths. One-and-a-half dozen would be hyphenated, otherwise you would technically be indicating 7 instead of 18. BE CAREFUL NOT TO INCLUDE THE FOLLOWING NOUN IN THE HYPHENATION. This is true even if the following noun is another number: Three-and-a-half thousand. One-and-a-half million. And dozens are tricky. Two-and-a-half-dozen eggs, but two-and-a-half dozen.
However, according to CMOS, if the fraction is not before a noun (and thus functioning as a compound adjective), then you do NOT hyphenate.
5. And not that this will happen very often, but when you have compound fractions in the numerator or denominator, for clarity, do NOT hyphenate the fraction. Ex: Forty-one fifty-sixths. Eighteen seventy-sixths.
6.When using a compound number larger than one hundred, only hyphenate the compound between twenty-one and ninety-nine. For example: Eight hundred and forty-three. Six thousand and twenty-one.
7. Ages. Three-year-old, forty-year-old woman, and eighty-one-year-old man are all hyphenated, according to Chicago Manual of Style. However, if the child is three years old (note plural), no hyphens are needed. Similarly, a woman can be forty years of age and not need a single hyphen. The most complex example is when you have an age range. The librarian was reading to a group of three- to ten-year-olds. Notice the space after the hyphen that follows three.
8. Percents are not hyphenated. Ten percent. A fifteen percent increase.
9. Centuries conform to the general rule for hyphenating a compound adjective. When it comes before the noun, include century in the hyphenation (in the case of twenty-first century and above). Afterward, do not (CMOS).
- It is now the twenty-first century.
- Eighteenth-century painting was realistic and ornate.
- Mid-twentieth-century architecture tended toward spare lines.
- Fourteenth-century monks were often scribes.
- Her writing style was nineteenth century.
- It was a half-hour session.
- The wait lasted a quarter hour.
I hope this was helpful. Keep writing. 🙂