When to Use a Comma before a Conjunction

The Quick Answer
When to use a comma before a conjunction.

If you're merging two sentences into one with a conjunction, then use a comma before the conjunction (e.g., I like fish, and I like chips. )

With lists, if there are just two list items, don't use a comma before the conjunction. With three or more, use a comma if you're an American.
  • Fish, chips, and peas ()
  • Fish, chips and peas ()
Brits should not use a comma.

However, if your organization advocates the Oxford Comma, use a comma. Also, if breaking convention makes your text clearer, then break convention.

Comma before And

This page is about when to use a comma before a conjunction (i.e., a word like and, or, and but).

Unfortunately, there is no simple rule like: always use a comma before and or never use a comma before and.

Use a Comma to Join Two Independent Clauses

When two standalone sentences (or independent clauses) are joined together using a conjunction (e.g., and, but, or), the conjunction should be preceded by a comma.

Examples (the conjunctions are shaded):
  • Our team was given 2 minutes' notice, but theirs had been training for weeks.
    • (When two complete "sentences" are merged into one using a conjunction, the conjunction should be preceded by a comma.)
  • I have spoken to Sarah, and she has confirmed the delivery date.
    • ("I have spoken to Sarah." + "She has confirmed the delivery date". The conjunction and is correctly preceded by a comma.)
  • I have spoken to Sarah, and confirmed the delivery date.
    • ("I have spoken to Sarah." + "confirmed the delivery date".
    The conjunction and should not be preceded by a comma in this example because confirmed the delivery date is not a complete sentence, i.e., it is not an independent clause. This is just a list with two list items: spoken to Sarah and confirmed the delivery date.)
  • We eventually found the cave, but Jack was not there.
  • We built the hut in an hour and then painted it.
    • (This is correct with no comma.)

Don't Use a Comma to Join Two List Items

When there are two items in a list, there is no need to separate the list items with a comma.

Examples:
  • Fish and chips
  • She would only eat ham and eggs.
  • I have never been to London, or Paris.
    • (With two list items, there is no need for the comma.)

With Three List Items, Use a Comma If You're an American (or an Advocate for the Oxford Comma)

When there are three or more list items, things start to get complicated. There a two conventions. Generally speaking (more on this below), Americans will use a comma, but Brits won't.

Examples:
  • Fish, chips, and peas ()
  • Fish, chips, and peas ()
  • Fish, chips and peas ()
  • I have never been to London, New York, or Paris. () ()
The comma before a conjunction in a list is called an Oxford Comma. Be aware that – despite the national conventions outlined above – lots of Brits use it, and lots of Americans omit it. So, the national conventions explained above are not strictly followed in either country. There are also times when you should break whatever convention you're following to make your text clearer.

The Oxford Comma causes great debate amongst grammarians. The bottom line is this: use the convention that will least annoy your boss (or readers) and then be consistent throughout your document.

Read more about commas in lists.
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See Also

What are conjunctions? What is an Oxford Comma? Commas in lists Conjunctions and semicolons