One hundred percent? Or 100%? Tips for writing numbers.

by Raymond DeLuca, English Grammar and Language Tutor

Students bring all sorts of different essays to the Writing Center, and each discipline has its own conventions when it comes to writing numbers. People are always surprised to learn that, yes, there are good and not so good ways to write numbers in English. So, this information will save you a headache. After all, it is not the best use of your time when writing an essay (especially when it’s due in a few hours) to get stuck thinking, well, is it “3” or “three”?

Just as there are different citation styles for citing sources in different academic fields, there are also different conventions for writing numbers. Each of the most common citation styles—MLA, APA, and Chicago– offers slightly different rules for writing numbers. You should always make sure you know what style and citation guidelines you should be following for a specific assignment. If you are writing a non-technical paper and can choose your style, I recommend following the MLA guidelines, which make a lot of sense and are commonly used in cases where you’re not using a lot of numbers.

Rule #1: When should you write out numbers and when should you use the number?

For papers in the humanities and in some social sciences, you will often use either the MLA or Chicago citation styles. In those styles, when you are writing a non-technical paper, you should write out numbers less than one hundred, using a dash for two-digit numbers: eight, fifteen, forty-five, sixty-two, eighty-seven, etc., etc.  And, for numbers over one hundred: 1,435; 2,870; 5,740; 11,480. Someone here is bound to ask: “Well, does that mean one trillion should be written as 1,000,000,000,000?” No, of course not. If the number (even if it’s above one hundred) can be easily expressed in words, then keep it in words: four hundred, eight thousand, three billion, nine quintillion, etc.

If you’re using APA style, you should generally only write out numbers 1-9 and use numerals for everything else. But there is an exception: If you are using a number at the beginning of the sentence, you should write it out.

Rule #2 What about percentages?

Just like with regular numbers, different style guides express different preferences for percentages.  I like the MLA style, which advises that for a percentage less than one hundred, you should write it in words: two percent, seventy-six percent, ninety-nine percent, but, for a percentage greater than one hundred, write it in numerals: 110 percent, 500 percent, 999 percent. Besides that, as you can see, in non-technical writing, it is better to use the word “percent” rather than the percent sign, “%.” It’s ugly.

In this case, Chicago and APA style both call for using use numbers in percentages.

Rule #3: What about years?

MLA, Chicago, and APA style all say that years are better written in numerals, not words: 1967, not “nineteen sixty-seven.” (Sometimes students write out the years to pad their paper’s word count; it’s not a good look! Everyone can see what you’re doing.) It’s also considered poor style to start a sentence with a year, i.e., “2020 has been a bad year.” You could rephrase that, writing instead: “Many people thought 2020 would be a better year.”

Rule #4: What about decades?

If you’re talking about a series of events that occurred in a certain decade, say, from 1980 – 1989, you can refer to that period in three different ways: the eighties, the ‘80s, or the 1980s. But stay clear of the “nineteen eighties.”

Rule #5: If you ever find yourself writing about a score or a court decision or a ratio, you should stick with numerals (even if said numbers are less than one hundred). For example, “The Red Sox were up 4-2 before losing 6-4,” or “The contentious 5-4 Supreme Court ruling says…”

These are obviously not the only situations you will encounter when you need to write a number, but these rules will help clear up some of the most common issues I’ve seen in student writing. Numbers can be as easy as one, two, three. If you find yourself writing a science or an econometrics paper, you may have to use way more numbers than you would otherwise, and you will need to make sure you are following the guidelines in your field. Generally, though, these five suggestions are good to keep in mind.

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