ACT English Comma Rules: The Only 6 Uses That Matter

Why Commas Are the Most Valuable Punctuation on the ACT

If there's one punctuation mark that can single-handedly move your student's ACT English score, it's the comma. Comma questions appear more frequently than any other punctuation concept on the ACT English section — typically 8 to 12 times per test. That's roughly 10-15% of the entire English section riding on whether your student knows when to use a comma and, just as importantly, when not to use one.

Here's what makes comma questions both frustrating and fixable: most students have a vague sense of comma rules from years of English class, but that vague sense leads to guessing. And guessing on comma questions is essentially a coin flip. The difference between a student who "sort of knows" comma rules and one who actually knows them can be 4-6 points on the English section.

At nGenius Prep, we've boiled comma usage down to exactly six rules. These six rules cover every legitimate comma use that appears on the ACT. If a comma doesn't serve one of these six functions, it doesn't belong in the sentence. Period.

Let's walk through each one.

The Golden Rule: Default Is NO Comma

Before we cover the six uses, your student needs to internalize this principle: the default is no comma. A comma should only appear if it has a specific job to do. If your student can't point to one of the six rules below and say "this is why the comma is here," the comma should be removed.

This is the opposite of how most students approach comma questions. They read a sentence, pause where it "feels right," and drop in a comma. The ACT punishes this approach ruthlessly. Unnecessary commas are wrong answers, and the ACT includes them as tempting traps in nearly every set of answer choices.

Teach your student to think of commas like tools in a toolbox. You don't grab a hammer unless you have a nail. You don't place a comma unless it's doing one of these six jobs.

Rule 1: Separating Items in a List

The Rule: When three or more items appear in a series, use commas to separate them.

Examples:

• •She packed her calculator, pencils, and a snack for test day.
• •The ACT tests reading, English, math, and science.
• •Students should arrive early, find their seat, and review their notes.

What the ACT tests: The ACT consistently uses the Oxford comma (the comma before "and" in a list), so your student should always include it. The trickier list questions involve items that are themselves phrases:

The study plan included reviewing grammar rules, practicing with timed sections, and analyzing mistakes from previous tests.

Each "item" is a full phrase, but the same rule applies — commas separate the items.

Watch out for: Two-item lists don't get a comma. "She packed her calculator and pencils" has no comma because there are only two items. The ACT loves offering answer choices that add a comma between just two items.

Rule 2: Joining Two Independent Clauses with a Coordinating Conjunction

The Rule: When two independent clauses (complete sentences) are joined by a coordinating conjunction (and, but, or, nor, for, so, yet), place a comma before the conjunction.

Examples:

• •Sarah studied for three weeks, and her score improved by four points.
• •The math section felt difficult, but Marcus finished every question.
• •You can take the ACT in April, or you can wait until June.

What the ACT tests: The key question is whether both sides of the conjunction are independent clauses. If the second part isn't an independent clause — if it doesn't have its own subject — no comma is needed.

Compare:

• •Sarah studied hard and improved her score. (No comma — "improved her score" isn't an independent clause; it shares the subject "Sarah.")
• •Sarah studied hard, and she improved her score. (Comma — "she improved her score" is an independent clause with its own subject.)

This distinction is one of the most frequently tested comma concepts on the entire ACT. Your student should practice identifying whether the words after "and" or "but" form a complete sentence on their own.

Memory trick: Cover everything before the conjunction. Can the remaining words stand alone as a sentence? If yes, add the comma. If no, don't.

Rule 3: After Introductory Elements

The Rule: When a sentence begins with an introductory word, phrase, or clause, follow it with a comma before the main clause begins.

Examples:

• •Unfortunately, the test center was overbooked. (Introductory word)
• •After three months of preparation, Eliana felt confident. (Introductory prepositional phrase)
• •When the proctor announced the start of the reading section, students opened their booklets. (Introductory dependent clause)
• •Running late to the test center, James nearly forgot his ID. (Introductory participial phrase)

What the ACT tests: The ACT primarily tests longer introductory elements — phrases and clauses, not single words. The most common pattern is an introductory dependent clause (starting with when, if, because, although, after, before, since, while) followed by a comma and then the main clause.

Critical distinction: When the dependent clause comes after the main clause, you typically don't need a comma:

• •Eliana felt confident after three months of preparation. (No comma needed)
• •After three months of preparation, Eliana felt confident. (Comma needed)

This front-vs-back distinction trips up students who think dependent clauses always need commas. Position matters.

Rule 4: With Adverbs and Adverbial Phrases

The Rule: When a transitional adverb or adverbial phrase interrupts the flow of a sentence, set it off with commas.

Examples:

• •The reading section, however, proved more challenging than expected.
• •Her math score, as a result, improved dramatically.
• •The test, in fact, was easier than the practice exams.

Common transitional words tested: however, therefore, moreover, furthermore, in fact, for example, on the other hand, as a result, in addition, nevertheless, consequently

What the ACT tests: Two main patterns:

1. 1.Mid-sentence transitions: These need commas on both sides. "The test however was easy" is wrong. "The test, however, was easy" is correct.

1. 1.Sentence-starting transitions: These need a comma after them. "However the test was easy" is wrong. "However, the test was easy" is correct.

The trap: Not every adverb gets commas. Short adverbs that are essential to the meaning of the sentence don't get set off. "She also studied science" doesn't need commas around "also." The commas are for transitional words that could be removed without changing the sentence's core meaning.

Test it: Remove the adverb or adverbial phrase. Does the sentence still make grammatical sense and convey its essential meaning? If yes, the commas belong. If removing the word changes the meaning significantly, skip the commas.

Rule 5: Isolating Non-Essential (Nonrestrictive) Phrases

The Rule: When a phrase adds extra information about a noun but isn't necessary to identify which noun you're talking about, set it off with commas.

Examples:

• •Dr. Martinez, who has taught AP Biology for fifteen years, recommends starting test prep early.
• •The ACT, which is accepted by all US colleges, is offered seven times per year.
• •My sister, a junior at Madison Academy, scored a 31 on her first attempt.

What the ACT tests: This is the essential vs. non-essential distinction, and it's one of the highest-value comma concepts on the test.

Essential (restrictive) — NO commas: Students who study consistently score higher on the ACT.

Here, "who study consistently" is essential because it tells us which students. Removing it changes the meaning — we'd be saying all students score higher, which isn't the intended claim.

Non-essential (nonrestrictive) — USE commas: Maria, who studied consistently, scored higher on the ACT.

Here, "who studied consistently" is extra information about Maria. We already know who we're talking about (Maria). Removing the phrase doesn't change which person we mean.

The test: Ask: "Does this phrase identify the noun, or does it just add extra detail about an already-identified noun?" If it identifies, no commas. If it just adds detail, use commas.

The "which" vs. "that" shortcut: On the ACT, "that" typically introduces essential clauses (no commas), while "which" typically introduces non-essential clauses (with commas). This isn't an absolute rule in all writing, but it's a reliable pattern on the ACT:

• •The book that I borrowed is on the table. (No commas — "that I borrowed" identifies which book)
• •The book, which I borrowed last week, is on the table. (Commas — extra detail about an already-identified book)

Rule 6: Setting Off Parenthetical Expressions

The Rule: When a word, phrase, or clause is inserted into a sentence as an aside or additional comment — an expression that interrupts the sentence's grammatical flow — set it off with commas.

Examples:

• •The ACT, unlike the SAT, includes a science reasoning section.
• •Test day, believe it or not, went smoothly.
• •Our tutor, Kyle, has helped hundreds of students improve their scores.
• •Madison, Alabama, is home to several excellent high schools.

What the ACT tests: Parenthetical expressions must have commas on both sides (unless they appear at the very beginning or end of a sentence). This is where students make their most common mistake — they add one comma but forget the other.

Think of parenthetical commas like parentheses: they always come in pairs. If you open the parenthetical aside with a comma, you must close it with one too.

Wrong: The ACT, unlike the SAT includes a science section. Wrong: The ACT unlike the SAT, includes a science section. Right: The ACT, unlike the SAT, includes a science section.

How to spot them: Remove the expression from the sentence. If the sentence still makes perfect grammatical sense and says what it needs to say, the expression is parenthetical and needs commas.

The ACT includes a science reasoning section. ✓ — Works fine without "unlike the SAT," confirming it's parenthetical.

Common ACT Comma Traps

Trap 1: Comma Between Subject and Verb

The ACT frequently offers answer choices that place a comma between a subject and its verb. This is almost always wrong.

• •Wrong: The student who studied the hardest, earned the highest score.
• •Right: The student who studied the hardest earned the highest score.

No matter how long and complex the subject is, don't separate it from its verb with a lone comma.

Trap 2: Comma Before or After a Preposition

Random commas before or after prepositions (of, in, at, for, with, to, by) are usually wrong unless another rule justifies them.

• •Wrong: She scored well on the test, in spite of her nerves.
• •Right: She scored well on the test in spite of her nerves.

Trap 3: Comma in a Compound Element (Not a Compound Sentence)

A compound verb (one subject, two verbs) doesn't get a comma:

• •Wrong: She studied for the ACT, and improved her score.
• •Right: She studied for the ACT and improved her score.

Remember: the comma-before-conjunction rule (Rule 2) only applies when both sides are independent clauses.

Trap 4: Too Many Commas

The ACT often includes answer choices that are littered with unnecessary commas. If an answer choice has commas everywhere and your student can't identify what job each comma is doing, that choice is probably wrong. Cleaner is almost always better.

Putting It Into Practice

Here's a practice approach we use with our ACT Edge students:

Step 1: The Comma Audit

Take any ACT English passage and circle every comma. For each one, identify which of the six rules it serves. If a comma doesn't fit any rule, it shouldn't be there. This exercise builds the habit of questioning every comma rather than accepting them passively.

Step 2: The Removal Test

For any comma question, try reading the sentence without the comma. Then with it. Which version follows the rules? Remember — the default is no comma. You need a reason to add one.

Step 3: The Pair Check

Every time your student places a comma for Rules 4, 5, or 6 (adverbs, non-essential phrases, parenthetical expressions), they should check: is there a matching comma on the other side? If they're adding one comma for a mid-sentence interruption, they need two.

Step 4: Timed Practice

Once the rules are solid, practice under time pressure. The English section demands speed — 36 seconds per question. Comma rules need to become automatic, not something your student reasons through slowly each time.

How Many Points Are We Talking About?

Let's be specific. If the ACT English section has 75 questions and roughly 8-12 of them involve comma decisions, that's 10-16% of the section. For a student currently scoring a 22 on English, getting just 6 more comma questions right could push that to a 25 or 26.

And here's the thing: comma questions are among the most learnable questions on the ACT. They're not testing reading comprehension or critical thinking — they're testing whether your student knows six specific rules. That's it. The rules don't change. The patterns don't change. The comma questions on the test your student takes next month will follow the same six rules as the questions on every ACT for the past decade.

This is pure preparation paying off.

What's Next

Comma rules are a piece of the larger ACT English puzzle. Once your student has these six uses mastered, they should move on to the other high-frequency grammar concepts: subject-verb agreement, verb tense, pronoun agreement, and apostrophes.

For structured, expert-led preparation that covers all of this in a clear sequence, explore our ScoreJump ACT prep program. Our approach breaks the test down into exactly what your student needs to know — no more, no less — and builds skills in the order that produces the fastest score improvement.

Have questions about where your student should start? Reach out to us — we're happy to help you figure out the best path forward.