ACT English · Punctuation
Comma Rules on the ACT: Every Rule, Named and Explained
Comma questions affect every single student who takes the ACT, whether you have a 21 on the English section or a 33. They make up about 12% of the ACT English section, and, believe me, they trick even the best grammar students.
This page covers every single comma rule on the ACT, including the most common mistakes our tutors see students make.
Important note about commas on the ACT: even the best grammar students miss easy comma questions. The reason is simple. The ACT is really good at making the wrong answer look correct. The wrong answer “sounds right” when you read the sentence out loud. If you read a sentence on the ACT out loud and it “sounds right,” you should immediately be suspicious. They might be trying to trick you.
Rules covered in this guide
| Rule | Named Method | Frequency |
|---|---|---|
| Joining two independent clauses (comma splices) | Comma-Clause Check | Very High |
| Commas with coordinating conjunctions (FANBOYS) | FANBOYS Split Test | High |
| Commas after introductory elements | Subject-First Test | Low |
| Commas around nonessential clauses and appositives (Comma Sandwiches) | Remove-and-Test Check | Very High |
| Commas in a series (the Oxford comma) | Series Scan | Medium |
| When NOT to use a comma: subject and verb | Subject-Verb Bridge Rule | Low |
| When NOT to use a comma: before “that” | That/Which Dividing Line | Low |
| Commas between dependent and independent clauses | Dependent Clause Detector | Medium |
Rule 1
Comma Splices — Joining Two Independent Clauses
Very High FrequencyA comma alone cannot join two independent clauses. An independent clause has a subject and a verb and can stand alone as a sentence. Joining two of them with only a comma creates a comma splice, which is always wrong on the ACT.
Named Method
The Comma-Clause Check
When you see a comma in an underlined portion, ask: is there a complete sentence on each side? If yes, a comma alone is not enough. You need a period, a semicolon, or a comma + FANBOYS conjunction to fix it.
✗ Incorrect
She studied all night, she passed the exam.
✓ Correct
She studied all night, so she passed the exam.
ACT-style practice question
The new library opened last spring, students immediately began using its expanded research database.
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Rule 2
Commas with Coordinating Conjunctions (FANBOYS)
High FrequencyWhen a coordinating conjunction (for, and, nor, but, or, yet, so) joins two independent clauses, place a comma before the conjunction. Do not use a comma before a conjunction that joins two phrases or two words — only two full independent clauses.
Named Method
The FANBOYS Split Test
Use your finger to cover up the conjunction and the comma before it. Read what’s on the left of the comma + FANBOYS. Read what’s on the right of the comma + FANBOYS. If each side is a complete sentence that can stand on its own (and they don’t have the exact same subject), using a comma + FANBOYS is correct.
So, just to review the FANBOYS Split Test: Step one is to split the sentence in half by placing your finger over the comma + FANBOYS. Step two is to read the clauses to determine if they are complete sentences. If they are complete sentences, use a comma followed by FANBOYS to join the clauses.
✓ Correct — two independent clauses
The coach gave a speech, and the team took the field.
✗ Incorrect — two verbs, one subject
The coach gave a speech, and took a bow.
ACT-style practice question
Marcus trained for months but the race was canceled due to weather.
Rule 3
Commas After Introductory Elements
Low FrequencyWhen a sentence begins with an introductory phrase or clause — before the main subject arrives — place a comma after it to separate it from the rest of the sentence. This applies to introductory adverb clauses, participial phrases, prepositional phrases, and transitional words.
Named Method
The Subject-First Test
Find the main subject of the sentence. If anything comes before it — a phrase, a clause, a transitional word — that opening material needs a comma after it. Ask: where does the main subject first appear? Everything before it is introductory.
✓ Correct
After the storm passed, the roads were cleared quickly.
✗ Incorrect
After the storm passed the roads were cleared quickly.
ACT-style practice question
Having reviewed all the evidence the jury reached a unanimous verdict in under two hours.
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Rule 4
Commas Around Nonessential Clauses and Appositives (aka Parenthetical Phrases aka Comma Sandwiches)
Very High FrequencyThis is super important. Comma Sandwiches are everywhere on the ACT. Don’t worry! They’re actually simple.
A Comma Sandwich is a clause or phrase that is “sandwiched” between two commas. Here’s an example: “My brother, who lives in Denver, visits every summer.” The phrase “who lives in Denver” is a comma sandwich. Here’s the key: Comma Sandwiches must use the same punctuation marks, meaning the phrase or clause must be surrounded by two commas, two dashes, or two parentheses. The phrase cannot be surrounded by one comma and one dash on either side.
Here’s an example of an incorrect comma sandwich: My brother – who lives in Denver, visits every summer.
How to Get Comma Sandwich Questions Correct Every Time
The Remove-and-Test Check
Information that is in a comma sandwich (like “who lives in Denver”) must be nonessential. This means that you should be able to remove that information — that phrase — from the sentence without changing the meaning or clarity of the sentence. If the sentence becomes vague or loses critical meaning, that information is essential and should not be surrounded by commas.
In the following example, test the “Remove-and-Test Check” method on the sentences about “My brother.” When you remove “who lives in Denver” from the sentence, the sentence still makes sense. That’s the point!
“My brother visits every summer” is a complete thought that does not need the clause “who lives in Denver.” So, “who lives in Denver” needs a comma sandwich around it.
✓ Nonessential — commas required
My brother, who lives in Denver, visits every summer.
✓ Essential — no commas
Students who miss the exam will receive a zero.
ACT-style practice question
The novel, which was published in 1851, remains one of the most studied works in American literature.
Rule 5
Commas in a Series (The Oxford Comma)
Medium FrequencyWhen listing three or more items in a series, separate each item with a comma. The ACT consistently uses the Oxford comma — the comma before the final “and” or “or” in a list. Treat this as required, not optional, on the ACT.
✓ Correct — Oxford comma included
She packed a tent, a sleeping bag, and a flashlight.
✗ Incorrect — Oxford comma missing
She packed a tent, a sleeping bag and a flashlight.
ACT-style practice question
The chef prepared a menu featuring roasted salmon braised short ribs, and a seasonal vegetable medley.
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Rule 6
When NOT to Use a Comma: Between Subject and Verb
Low FrequencyNever place a comma directly between a subject and its verb when nothing nonessential comes between them. This is one of the most common comma errors on the ACT — students add a comma because the subject is long, but length never justifies a comma before the verb.
Named Method
The Subject-Verb Bridge Rule
Find the subject. Find the main verb. Is there a comma between them with no nonessential phrase to justify it? If yes, that comma is wrong — delete it. The subject and verb are bridged; nothing interrupts them unless a set of paired commas wraps a nonessential phrase.
✗ Incorrect — comma between subject and verb
The results of the three-year study, surprised the research team.
✓ Correct — no comma
The results of the three-year study surprised the research team.
ACT-style practice question
The decision to relocate the company’s headquarters to Austin, surprised longtime employees and investors alike.
Rule 7
When NOT to Use a Comma: Before “That” in Restrictive Clauses
Low Frequency“That” introduces essential (restrictive) clauses — clauses that define or limit the noun they follow. Because these clauses are essential, they never get commas. “Which,” by contrast, introduces nonessential clauses and does take commas. This that/which distinction is a reliable ACT pattern.
Named Method
The That/Which Dividing Line
“That” = essential = no commas. “Which” = nonessential = commas. If you can swap “which” for “that” without losing meaning, you likely have a restrictive clause and shouldn’t use commas. If removing the clause makes the noun vague, it’s restrictive — use “that,” no commas.
✗ Incorrect — comma before “that”
The policy, that was passed last year affects all employees.
✓ Correct — no comma before “that”
The policy that was passed last year affects all employees.
ACT-style practice question
The bridge that engineers had flagged as structurally deficient was finally closed to traffic.
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Rule 8
Commas Between Dependent and Independent Clauses
Medium FrequencyA dependent clause cannot stand alone as a sentence — it depends on an independent clause to complete its meaning. When a dependent clause comes before the independent clause, use a comma to separate them. When the dependent clause comes after the independent clause, no comma is needed. The position of the dependent clause determines whether you use a comma.
Named Method
The Dependent Clause Detector
Find the subordinating conjunction — words like “although,” “because,” “since,” “when,” “while,” “if,” “unless,” “after,” “before,” and “even though.” These words signal a dependent clause. Then ask: does the dependent clause come first or second in the sentence?
Dependent clause first → comma required. Independent clause first → no comma. A simple way to remember it: if the sentence starts with a subordinating conjunction, it needs a comma. If the subordinating conjunction appears in the middle, it usually does not.
✓ Correct — dependent clause first
Although she studied for weeks, she still found the exam difficult.
✓ Correct — independent clause first
She still found the exam difficult although she studied for weeks.
ACT-style practice question
Because the city council had not approved the budget revision the construction project was delayed until the following spring.
Quick-Reference Summary: All 8 ACT Comma Rules
| Rule | Named Method | Frequency |
|---|---|---|
| Joining two independent clauses (comma splices) | Comma-Clause Check | Very High |
| Commas with coordinating conjunctions (FANBOYS) | FANBOYS Split Test | High |
| Commas after introductory elements | Subject-First Test | Low |
| Commas around nonessential clauses (Comma Sandwiches) | Remove-and-Test Check | Very High |
| Commas in a series (the Oxford comma) | Series Scan | Medium |
| When NOT to use a comma: subject and verb | Subject-Verb Bridge Rule | Low |
| When NOT to use a comma: before “that” | That/Which Dividing Line | Low |
| Commas between dependent and independent clauses | Dependent Clause Detector | Medium |
How to Approach Comma Questions on Test Day
Tip 1
Find independent clauses. Knowing where the main subject and main verb are in the sentence is critical. Once you know where the main subject(s) and verb(s) are and how many independent clauses there are, the questions become much easier.
Tip 2
There is only one right answer. Only one answer choice can be grammatically correct. Do not let the ACT trick you into thinking two options are “okay.”
Tip 3
When you practice, review the questions you get wrong. Read the explanations for the wrong answers. Understand why the answer choice you selected is incorrect on the ACT. The ACT is essentially the same test every time. So, if you learn from your mistakes, you won’t make them when you see the same type of question next time.
Common Questions About ACT Comma Rules
This ACT trick is known as the compound predicate trap. The subject, “I,” is the subject of both predicates (both of the verbs). This is a common ACT trick. There is only one independent clause, so there is no need for the comma + FANBOYS.
Corrected version: “I went to lunch on Saturday but had no time to look over the menu.”
This ACT trick is called the conjunctive adverb trap. That just means that words like “however,” “therefore,” and “nevertheless” are NOT part of FANBOYS.
Here’s how to use “however” correctly on the ACT:
Option 1 — Following a period: “Julius wanted to cross the river. However, his troops were not thrilled with this idea.”
Option 2 — Following a semicolon: “Julius wanted to cross the river; however, his troops were not thrilled with this idea.”
Option 3 — Middle of the sentence (but not taking the place of FANBOYS): “Julius wanted to cross the river. His troops, however, were not thrilled with the idea.”
Option 4 — End of a sentence: “Julius wanted to cross the river. His troops were not thrilled with the idea, however.”
Cross out all of the unnecessary information with a pencil. Seriously. If there is a phrase that is not part of the underlined section and does not have the main subject or the main verb in it, physically cross it out with your pencil. This will strip the confusing clutter from the sentence and help you understand what’s happening in the sentence.