Time and Numbers

A           D       F                         M   N   O   P               T               Y  

A

ages
Age terms are hyphenated in both noun and adjective forms (except as in the last two examples below). The examples apply equally to ages expressed as numerals. (chicago 16, 7.85, p.375)

a three-year-old
a five-year-old car
a two-and-a-half-year-old child
a fifty-five-year-old woman
a group of eight- to ten-year olds

but
seven years old
eighteen years of age

D

dates (in text)
On October 6, 1999, he withdrew from the race.
The April 1, 2002, report showed no decline in sales.
In March 2003 he graduated high school.
The March 2003 graduation was a stunning success.
 
decades
Decades are either spelled out (as long as the century is clear) and lowercased, or expressed in numerals. Chicago calls for no apostrophe to appear between the year and the s unless the less formal version is used.

the nineties
the 1980s and 1990s (or, less formally, the 1980s and '90s)

(Chicago Manual of Style 16, 9.34)

F

fewer — less
Use “fewer” when describing a (noun) that can be counted. Use “less” when describing a (noun) that cannot be counted:

We have fewer students in the class than last year.
There is less tension among students than ever before.

 
fractions

Simple fractions
Simple fractions are spelled out and hyphenated in noun, adjective, and adverb forms, except when the second element is already hyphenated. In the rare event that individual parts of a quantity are emphasized, as in the last example, the fraction is spelled open. (chicago 16, 7.85 and 9.14)

one-half, two-thirds, one twenty-fifth
one and three-quarters, a two-thirds majority
three-quarters done
a one twenty-fifth share
She has read three-fourths of the book.
Four-fifths of the students are boycotting the class.
A two-thirds majority is required.

but
We divided the cake into four quarters; I took three quarters, and my brother one.

Whole numbers plus fractions
Quantities consisting of whole numbers and simple fractions may be spelled out if short but are often better expressed in numerals (especially if a symbol for the fraction is available, as in the examples here. Also, as in the last example, if the number is used as a modifier, the entire phrase is hyphenated. (chicago 16, 9.15)

We walked for three and one-quarter miles.
I need 6¾ yards of the silk fabric.
Lester is exactly 3 feet 5¼ inches tall
Letters are usually printed on 8½″ x 11″paper.
They just finished a two-and-a-half-mile run.

M

midnight
See “noon and midnight” under “time of day” (below).
 
money

dollar amounts
five dollars
11 dollars
$5 [for less formal purposes]
$40 million
from $5.74 to $6.00

more to come . . .

monthlong
 

N

noon
See “noon and midnight” under “time of day” (below).
 
numbers in text
Numbers one through nine should be written out in formal writing:
There are five students absent today.

Numbers greater than nine should not be written out:

There are 35 trainees in the program.

But
When the number begins the sentence, write it out:

Thirty-five students are enrolled in the program.

If a number less than nine is used with a number greater than nine, use your best judgment in each scenario, erring on the side of consistency within the sentence:

He requested that we keep the price between nine and ten dollars.
His speed increased from 0 to 90 in a matter of seconds.

O

one-on-one (adj, n)
 
one-to-one (adj)
The water-to-salt content was a one-to-one ratio.

P

part time (adv)
She goes to school part time.
 
part-time (adj)
All were part-time employees.
 
part-timer (n)
 
per
See “a, per”
 
percentages
Spell out “percent” in text. It is OK to use the percent symbol (%) in charts and graphs or when the majority of the textual content is scientific, mathematical, or statistical (such as research reports and summaries). (Chicago 16, 9.18, p. 470)

Fewer than 3 percent of the employees used public transportation.
With 90–95 percent of the work complete, we can relax.
A 75 percent liklihood of winning is worth the effect.
The treatment resulted in a 20% to 25% increase in reports of night blindness.

 
telephone numbers
Always format phone numbers like this:

(617) 555-1212.

Don't use the format 617-555-1212 or 1-617-555-1212.

Do not put a comma before the extension.

(617) 555-1212 ext. 1234.

T

time of day

Numerals versus words
Times of day in even, half, and quarter hours are usually spelled out in text. With o'clock, the number is always spelled out:

The meeting lasted until half past three.
The family always ate dinner at seven o'clock.
He left the office at a quarter of four. [The a is optional when using quarter.]

But numerals are used (with zeros for even hours) when the exact time is emphasized. The Chicago Manual of Style recommends lowercase a.m. and p.m., though these can also be set in small capitals, with or without periods.

The first train leaves at 5:22 a.m. and the last at 11:00 p.m.
She caught the 6:20 p.m. flight.
Please attend a meeting in Grand Rapids, Michigan, on December 5 at 10:30 a.m. (EST).

Noon and midnight
Except in the 24-hour system, numbers should never be used to express noon or midnight (except, informally, in an expression such as twelve o'clock at night). The term 12:00 p.m. is ambiguous, if not illogical. In the second example, note the double date for clarity:

The meeting began at 9:45 a.m. and was adjourned by noon.
Rodriquez was born at midnight, August 21–22.

 
time sheet (n)
Don't forget to turn in your time sheet.
 
timetable (n)
According to the attached timetable…
 
timeline (n)
A rough timeline follows.
 
two-faced (adj)
That is a two-faced argument.
 
twofold (adj)
The reason for this is twofold.

Y

year-round (adj)
Our students work hard year-round.