How to Use Commas: Rules, Examples, and Common Mistakes

Why Commas Matter More Than You Think

The comma is the most frequently used punctuation mark in English, and it is also the most frequently misused. A single comma can change the meaning of a sentence entirely. Consider the difference between "Let's eat, Grandma" and "Let's eat Grandma." One is an invitation to dinner. The other is a horror movie.

That example gets passed around a lot, but it illustrates something real: commas carry meaning. They tell readers where to pause, how to group words together, and which parts of a sentence are essential. When you place commas correctly, your writing becomes clearer and more professional. When you place them incorrectly, your sentences become confusing or say something you did not intend.

This guide covers every major comma rule you need to know, with plenty of examples along the way. If you want to check your comma usage automatically, Rephrasely's comma checker can scan your writing and flag errors in seconds.

Commas in Lists and Series

The most familiar comma rule is probably this one: use commas to separate three or more items in a list. The items can be single words, phrases, or even clauses.

• Words: She bought apples, oranges, and bananas.
• Phrases: The dog ran through the yard, across the street, and into the park.
• Clauses: He said that he was tired, that he wanted to go home, and that he would call in the morning.

This rule is straightforward, but there is one part of it that sparks more debate than almost any other punctuation question: the Oxford comma.

The Oxford Comma Debate

The Oxford comma (also called the serial comma) is the comma placed before the conjunction in a list of three or more items. In the sentence "She bought apples, oranges, and bananas," the comma after "oranges" is the Oxford comma.

Some style guides require it (Chicago Manual of Style, APA). Others discourage it (AP Style). So who is right? Both sides have valid arguments, but the Oxford comma does prevent ambiguity in certain situations.

The safest approach is to use the Oxford comma consistently. It rarely causes confusion, and leaving it out sometimes does. If you are writing for a publication or organization, follow their style guide. Otherwise, pick a convention and stick with it throughout your document.

Commas in Compound Sentences (The FANBOYS Rule)

When you join two independent clauses with a coordinating conjunction, place a comma before the conjunction. The seven coordinating conjunctions are easy to remember with the acronym FANBOYS: For, And, Nor, But, Or, Yet, So.

An independent clause is a group of words that can stand alone as a complete sentence. If both sides of the conjunction could work as separate sentences, you need a comma.

Here is the part that trips people up: do not use a comma before a conjunction if the second part is not an independent clause.

• No comma needed: I wanted to go for a run but changed my mind. ("Changed my mind" is not a complete sentence on its own.)
• No comma needed: She washed the dishes and dried them. ("Dried them" cannot stand alone.)

If you drop the conjunction entirely and just smash two independent clauses together with only a comma, you create a comma splice, which is one of the most common grammatical errors in English. More on that later.

Commas After Introductory Elements

When a sentence starts with a word, phrase, or clause that comes before the main subject and verb, follow that introductory element with a comma. This is one of the most useful comma rules because it immediately makes your writing easier to read.

Introductory Words

Single introductory words like "however," "meanwhile," "unfortunately," "yes," "no," and "well" take a comma after them.

• Unfortunately, the flight was delayed by three hours.
• Yes, I would love to come to the party.
• Meanwhile, the cat had knocked over the vase.

Introductory Phrases

Prepositional phrases, participial phrases, and infinitive phrases at the beginning of a sentence usually need a comma.

• Prepositional: After the long meeting, everyone went to lunch.
• Participial: Running late for work, she skipped breakfast.
• Infinitive: To finish the project on time, they worked through the weekend.

There is a minor exception: very short prepositional phrases (two or three words) sometimes drop the comma if there is no risk of misreading. "In June we moved" is acceptable, though "In June, we moved" is also fine. When in doubt, include the comma. It never hurts clarity.

Introductory Dependent Clauses

When a dependent clause comes before the main clause, use a comma to separate them. A dependent clause starts with a subordinating conjunction like "because," "although," "when," "if," "since," "after," or "while."

• Because the roads were icy, school was canceled.
• Although he studied hard, he did not pass the exam.
• When the timer goes off, remove the cake from the oven.

Notice that this rule only applies when the dependent clause comes first. When the main clause comes first, you generally do not need a comma: "School was canceled because the roads were icy."

Commas with Nonrestrictive (Nonessential) Clauses and Phrases

This rule is one of the trickiest, but once you understand the logic behind it, it becomes much easier. The key question is: Is this information essential to the meaning of the sentence, or is it extra?

A nonrestrictive (nonessential) element adds information that is interesting or helpful but could be removed without changing the core meaning of the sentence. Set it off with commas.

A restrictive (essential) element is necessary to identify exactly who or what you are talking about. Do not use commas around it.

A useful shortcut: "which" clauses are usually nonrestrictive (use commas), and "that" clauses are usually restrictive (no commas). This is not an absolute rule, but it holds true most of the time in American English.

Commas with Appositives

An appositive is a noun or noun phrase that renames or describes another noun right beside it. When the appositive is nonessential, surround it with commas. When it is essential for identification, leave the commas out.

• Nonessential: Barack Obama, the 44th president, wrote a memoir. (There is only one Barack Obama, so "the 44th president" is extra information.)
• Nonessential: My dog, a golden retriever, loves swimming. (If you have only one dog, the breed is additional detail.)
• Essential: The novelist Toni Morrison won the Nobel Prize. ("Toni Morrison" identifies which novelist. Without the name, the sentence is too vague.)

The test is the same as for nonrestrictive clauses: can you remove the appositive and still know exactly who or what the sentence is about? If yes, use commas. If no, skip them.

Commas for Direct Address

When you address someone by name (or by a title, nickname, or other identifier), set that name off with commas. This rule is what saves grandmothers everywhere.

• Sarah, can you pass me the salt?
• I think, Professor, that you may be mistaken.
• Thank you for your help, Dr. Patel.
• Ladies and gentlemen, welcome to the show.

Notice that the comma goes before the name when it appears at the end, after the name when it appears at the beginning, and on both sides when it appears in the middle of the sentence.

Commas with Dates, Addresses, and Numbers

Commas have several conventional uses in dates, geographical names, addresses, and large numbers. These rules are not about grammar so much as formatting, but getting them wrong looks sloppy.

Dates

In the month-day-year format, use commas after the day and after the year (if the sentence continues).

• She was born on March 15, 1990, in Portland.
• The event is scheduled for December 1, 2026, at the convention center.

If you write only the month and year, no comma is needed: "She graduated in May 2020."

If you use the day-month-year format (common in British English), no commas are needed at all: "She was born on 15 March 1990 in Portland."

Addresses and Geographical Names

Use commas to separate the parts of an address or place name. Also place a comma after the last element if the sentence continues.

• She lives in Austin, Texas, with her family.
• The office is at 42 Oak Street, Suite 300, Denver, Colorado, near the park.

Do not place a comma between the state and the ZIP code: "Denver, Colorado 80203."

Numbers

Use commas in numbers with four or more digits to separate groups of three, counting from the right: 1,000; 52,345; 1,000,000. Exceptions include years (2026), page numbers, and addresses (1520 Elm Street).

Commas with Coordinate Adjectives

When two or more adjectives independently modify the same noun, they are called coordinate adjectives, and you should separate them with commas.

• She wore a long, elegant dress.
• It was a cold, rainy morning.
• He is an honest, reliable employee.

But not all adjacent adjectives are coordinate. Sometimes the first adjective modifies the combination of the second adjective plus the noun, rather than modifying the noun on its own. These are called cumulative adjectives, and they do not take commas.

• She wore a beautiful red dress. (Not "beautiful, red dress.")
• He drives an old pickup truck. (Not "old, pickup truck.")

There are two quick tests to tell whether adjectives are coordinate:

1. The "and" test: Can you put "and" between the adjectives and have the sentence still sound natural? "Long and elegant dress" works. "Beautiful and red dress" sounds awkward.
2. The swap test: Can you reverse the order of the adjectives? "Elegant, long dress" works. "Red beautiful dress" does not.

If both tests pass, the adjectives are coordinate and need a comma. If either test fails, they are cumulative and should not have one.

Commas with Quotations

When you introduce a quotation with a phrase like "she said" or "he wrote," use a comma to separate the attribution from the quoted material.

• She said, "I will be there by noon."
• "I will be there by noon," she said.
• "I will be there by noon," she said, "if the traffic is not too bad."

If the quotation is introduced with "that," do not use a comma: She said that she would be there by noon.

Also, if the quoted material is a question or exclamation, the question mark or exclamation point replaces the comma: "Are you coming?" she asked. (Not "Are you coming?," she asked.)

Commas with Conjunctive Adverbs and Transitional Phrases

Conjunctive adverbs like "however," "therefore," "moreover," "furthermore," "nevertheless," and "consequently" are not conjunctions. They cannot join two independent clauses with just a comma the way FANBOYS conjunctions can. Instead, use a semicolon before the conjunctive adverb and a comma after it, or start a new sentence.

For a full breakdown of how semicolons work alongside commas, see our guide on semicolon rules.

Commas to Prevent Misreading

Sometimes a sentence is grammatically complete without a comma, but a comma is still needed so the reader does not stumble. If a sentence could be misread on first pass, add a comma for clarity.

• Confusing: After eating the dog took a nap.
• Clear: After eating, the dog took a nap.

• Confusing: Outside the snow was falling.
• Clear: Outside, the snow was falling.

• Confusing: For most the rules are straightforward.
• Clear: For most, the rules are straightforward.

This is less of a formal rule and more of a general principle: when clarity and correctness conflict, choose clarity. A comma that makes a sentence instantly readable is always the right call, even if a strict grammarian might say it is optional.

Common Comma Mistakes

Knowing the rules is half the battle. The other half is knowing where commas do not belong. Here are the mistakes that come up most often.

1. The Comma Splice

A comma splice happens when you join two independent clauses with nothing but a comma. It is one of the most common errors in English writing.

• Wrong: The sun was setting, we headed home.
• Right: The sun was setting, so we headed home. (Add a FANBOYS conjunction.)
• Right: The sun was setting; we headed home. (Use a semicolon.)
• Right: The sun was setting. We headed home. (Make two sentences.)

Comma splices are easy to produce when you are writing quickly. If you suspect your writing might contain some, run it through a punctuation checker for a fast review.

2. Comma Between Subject and Verb

Do not place a comma between a subject and its verb, even when the subject is long.

• Wrong: The teacher who organized the field trip, reminded students to bring lunch.
• Right: The teacher who organized the field trip reminded students to bring lunch.

• Wrong: Running five miles every morning before work, is exhausting.
• Right: Running five miles every morning before work is exhausting.

This error often happens because the writer "hears" a pause after a long subject and wants to reflect it in punctuation. Resist the urge. The reader does not need a comma there, and inserting one breaks the sentence's grammatical backbone.

3. Comma Before "That" in Restrictive Clauses

As discussed earlier, restrictive "that" clauses do not take commas.

• Wrong: The book, that she recommended, was excellent.
• Right: The book that she recommended was excellent.

4. Comma After a Coordinating Conjunction

The comma goes before the FANBOYS conjunction in a compound sentence, not after it.

• Wrong: I wanted to go but, it was raining.
• Right: I wanted to go, but it was raining.

5. Overusing Commas with Short Introductory Elements

While commas after introductory elements are generally a good idea, stacking unnecessary commas around very short phrases or single adverbs midsentence can make writing feel choppy.

• Choppy: Then, she, suddenly, ran, out of the room.
• Better: Then she suddenly ran out of the room.

Not every adverb needs to be fenced off with commas. Use them when they genuinely improve readability, not out of habit.

6. Comma Before "Because" When It Creates Ambiguity

Usually, you do not place a comma before "because" when the main clause comes first. However, there is an exception when a negative main clause plus "because" could be misread.

• Ambiguous: She did not leave because she was afraid. (Did she stay because of fear, or did she leave for a different reason?)
• Clear: She did not leave, because she was afraid. (The comma clarifies: she stayed, and the reason was fear.)

Quick-Reference Comma Cheat Sheet

Frequently Asked Questions About Commas

What is the Oxford comma, and should I use it?

The Oxford comma is the comma placed before the conjunction in a list of three or more items (e.g., "apples, oranges, and bananas"). Whether you should use it depends on the style guide you follow. AP Style generally omits it, while Chicago and APA require it. If no style guide governs your writing, using the Oxford comma is the safer choice because it prevents ambiguity in sentences where list items could be confused with appositives.

What is a comma splice, and how do I fix one?

A comma splice occurs when two independent clauses (complete sentences) are joined with only a comma and no conjunction. For example, "I love coffee, I drink it every morning" is a comma splice. You can fix it by adding a coordinating conjunction ("I love coffee, and I drink it every morning"), using a semicolon ("I love coffee; I drink it every morning"), or splitting the clauses into two sentences. Our comma splice guide walks through this in greater detail.

Do I always need a comma before "and"?

No. You need a comma before "and" in two specific situations: when it joins two independent clauses in a compound sentence, and when it appears before the last item in a list of three or more (if you use the Oxford comma). You do not need a comma before "and" when it connects two words, two phrases, or two dependent clauses: "She sings and dances" needs no comma.

Should I put a comma before "because"?

Generally, no. When "because" introduces a reason after a main clause, no comma is needed: "She left early because she was tired." However, add a comma when a negative main clause might create ambiguity: "He did not call her, because he was busy" (the comma clarifies that busyness was the reason he did not call, rather than suggesting he called for a different reason).

How do I know if adjectives are coordinate and need a comma?

Apply two tests. First, try inserting "and" between the adjectives. If the sentence still sounds natural ("long and winding road"), they are coordinate. Second, try reversing their order. If the sentence still works ("winding, long road"), they are coordinate and need a comma. If either test fails ("big and red barn" sounds off), the adjectives are cumulative, and no comma is needed.

Is it ever wrong to use a comma after an introductory word?

Very rarely. Commas after introductory words like "however," "therefore," and "unfortunately" are standard and expected. Some writers omit the comma after very short introductory elements like "Then" or "So" at the start of a sentence, and this is acceptable when no misreading is possible. But in formal or academic writing, including the comma is almost always the right move.

Can I use a comma before "which"?

Yes, and in American English, you usually should. "Which" typically introduces a nonrestrictive (nonessential) clause, which means it needs a comma: "The car, which was red, sped past." If you find yourself writing a restrictive clause, use "that" instead of "which" and skip the comma: "The car that was red sped past." British English is more flexible about using "which" in restrictive clauses, but the comma distinction still applies.

How can I check my writing for comma errors?

Reading your work aloud is a good first step. If you pause naturally, a comma may be needed. If you stumble over a comma, it may be unnecessary. For a more thorough check, use an automated tool like Rephrasely's comma checker, which scans your text and highlights misplaced, missing, or unnecessary commas so you can fix them quickly.