• 2-minute read
• 6th May 2022

18th or Eighteenth? How to Write Centuries in Formal Writing

If you’re writing a research paper, marketing copy, or other professional document, you’ll want to know how to write dates and centuries correctly. Should you use numbers or words? Is it necessary to hyphenate or capitalize centuries? And, finally, just when did the 18th century take place? Read on for more!

Numbers Versus Words

There is no hard-and-fast rule about when to use numbers and when to use words in writing centuries, as long as you are clear and consistent. A guideline that is often adopted is that centuries after the tenth are represented using numerals (e.g., “16th century”), whereas earlier centuries are spelled out in words (e.g., “seventh century”); this is the rule that is followed by this blog post. If you’re using a style guide, however, it’s always worth checking its specifications.

When to Hyphenate Centuries

When centuries are used as adjective phrases preceding the nouns they modify, they are hyphenated:

It’s a 21st-century problem.

The ninth-century church is situated in the heart of the village.

However, when a century is used as a noun phrase, you should not use a hyphen:

The 20th century was an era of technological innovation.

Napoleon invaded Russia in the 19th century.

This is consistent with genera hyphenation rules.

When to Capitalize Centuries

There’s a simple answer to this question: never! While you may come across the capitalization of centuries in writing (e.g., “12th Century”), it’s never correct, as “century” is simply a measure of time and not a proper noun.

How to Number Centuries

This is a slightly more confusing issue. Many people assume that the 18th century, for example, lasted from 1800 to 1899; the clue’s in the name, right? Wrong! The first century started in the year 1 A.D. and lasted until the year 100, so therefore, the second century lasted from 101 to 200. Therefore, the 18th century consists of the 1700s rather than the 1800s.