The way you type centuries, dates and numerals in essays, term papers and other written work generally depends on the style guide you’re expected to follow. Some of the accepted styles you might encounter are Chicago Manual of Style (Chicago), Modern Language Association (MLA), and APA, the style guide of the American Psychological Association. Be sure to always follow the most updated guidelines for your specific style guide. The APA has a few rules when it comes to writing centuries, dates and numerals in general.
How to Write Out Numerals in APA Style
Generally, the APA requires numerals from one to nine to be spelled out as words, and numerals 10 and above to be written as numbers. For example:
- James has eaten nine apples.
- Maggie has sharpened 15 pencils.
The only exception is when the double-digit number appears at the beginning of the sentence. Since a sentence cannot begin with a numeral, spell out both single-digit and double-digit numbers if they appear as the first word in a sentence. For example:
- Fifteen years ago, he immigrated to the United States (correct)
- 15 years ago, he immigrated to the United States (incorrect)
How to Write Out Centuries in APA Style
When it comes to writing dates, ages and units of time in general, the rules differ from writing numerals in general. In these cases, the APA requires writing numerals regarding of the number. Thus, a century is written as a number, regardless of whether it is under ten or above 10.
The first example follows the APA guidelines, but the second one does not:
- The internet was invented in the 20th century. (correct)
- The internet was invented in the twentieth century. (incorrect)
Similarly, the first example follows the APA guidelines, but the second does not:
- The Early Medieval Period started in the 6th century. (correct)
- The Early Medieval Period started in the sixth century. (incorrect)
In other words, don't type out the century in APA format, but always write it as a numeral.