Are Million, Billion, and Trillion Capitalized?

With all the recent talk about millionaires, billionaires, stock markets and wealth gaps you might be wondering about how to properly write about those topics: is millionaire capitalized? How should I write the number as a word?

While spelling out numbers and using figures is a little bit of a gray area and left to the writers’ discretion, for example when it comes to hyphenating large numbers or spelling them outright vs using abbreviations.

Are These Words Capitalized?

However, a golden rule of writing numbers is that you don’t capitalize the word when spelling them out: that would be incorrect. So, million, billion, hundred, thousand are NOT capitalized, and neither are the words “billionaire” or “millionaire” as they are considered to be professions, and they follow the spelling rules of that class.

However, the first letter of million can be capitalized when abbreviated, as in “his net worth is well over $1,000,000MM” or “The stock market received an injection of $3,697,834Mil to keep it from collapsing”.

Origin of These Words

The term “billion” has been around since the sixteenth century, originally having a very direct meaning of “million to the power of two” or a thousand million. The word was of Latin origin and didn’t enter the English language until around the end of the seventeenth century. There was a brief period of time, specifically in British English, when the word referred to a million millions, and while the word has lost that meaning in the UK, it actually never had that definition in American English. When it comes to whether or not the word is capitalized, you have to look at its positioning in what you’re reading. Should “billion” be in a title, you would capitalize it as all nouns are capitalized in titles, the same is true if billion happens to be the first word in a sentence. Billion by itself in the middle of a sentence, however, is left lower case due to it not being a proper noun.


Capitalize My Title is a dynamic title capitalization tool used to make sure your titles or headlines use proper capitalization rules according to various style guides include APA, AP, MLA, and Chicago. It also counts your words and checks for grammar issues.

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