Howard Levy, principal of Red Rooster Group, asks the following questions about proper style for percentages and time:
When you have a range of numbers referred to in a sentence, do you use an en dash or the word “to”? As in “20 to 40%” or “20 – 40%”?
Also, would you use the % sign after both the 20 and the 40?
What about time ranges? Do you need to use the :00 in all cases, even if some times start at :30, as in 6 – 7:30 pm vs. 6:00 – 7:30?
All excellent questions. As is typical when dealing with English grammar rules and style guidelines, the answers depend on the circumstances.
- When working with a technical document, the standard convention calls for a numeral and the percentage sign. Ex. The control group experienced a 5%–7% reduction in discomfort.
- In nontechnical text, the convention is to use the numeral with the word percent. Ex. Marci predicted a 75 percent chance that John would cancel their date.
- That being said, The Chicago Manual of Style advocates use of the percentage symbol in nontechnical text that’s chock-full of percentages. Direct-response marketing copy, which relies heavily on specific proof, falls into this category. (Plus, testing shows that the percentage sign does a better job of grabbing readers’ attention.) Ex. This little-known stock produced gains of 286% after only six months.
Beyond that, using “to” versus an en dash or opting for one or two percentage signs depends on house style or client preference. The style selected simply needs to be consistent—certainly within the document and preferably throughout the organization’s materials.
Time of Day
Use numerals—including the zeros for even hours—when emphasizing exact time. (Times ranges fall in this category.) Ex. The meeting was scheduled to start at 6:00 p.m. and end at 7:30 p.m.
When referring to time of day in even, half or quarter hours, spell it out. Ex. The wedding ceremony begins at two thirty.
If you’re curious, the appropriate style for abbreviating ante meridiem and post meridiem is either lowercase with periods (a.m. and p.m.) or small caps without periods (which I can’t figure out with WordPress’s limited formatting options).