Commas on the ACT do only four jobs: they set off an introductory element, they surround non-essential information in a matching pair, they separate items in a series, and they join two independent clauses when a FANBOYS conjunction is there to help. If a comma in an answer choice isn't doing one of those four things, it almost certainly doesn't belong. That one idea will carry you through most comma questions you see, and it's a lot friendlier than trying to memorize a list of twenty exceptions.
The four jobs a comma is allowed to do
- After an introductory element. Before the last round of edits, Maya reread her outline. The comma tells you where the setup ends and the real sentence begins.
- Around non-essential information. My chemistry teacher, who runs the robotics club, stayed late on Thursdays. Lift the middle out and the sentence still works, so it gets a pair of commas.
- Between items in a series. She packed granola bars, a water bottle, and two pencils.
- Before a FANBOYS conjunction joining two complete sentences. The bus was late, so we started the meeting without him. FANBOYS is for, and, nor, but, or, yet, so.
Non-essential information always travels in a pair
This is the rule students lose the most points on, and it's an easy fix. If you open a non-essential phrase with a comma, you have to close it with one too. Our coach, a former sprinter left before halftime is wrong because the phrase never closes. Our coach, a former sprinter, left before halftime is right. Try the deletion test: if you can remove the phrase and still have a working sentence, it needs commas on both sides.
Correct versus incorrect, side by side
- Incorrect: The students who finished early, went to the library. Correct: The students who finished early went to the library. The comma was splitting the subject from its verb.
- Incorrect: Jordan studied all weekend, he still felt nervous. Correct: Jordan studied all weekend, but he still felt nervous.
- Incorrect: After the storm passed we walked down to the pier. Correct: After the storm passed, we walked down to the pier.
- Incorrect: She wrote the essay, and revised it twice. Correct: She wrote the essay and revised it twice. Two verbs sharing one subject do not need a comma between them.
How the ACT actually tests commas
The most common trap is the extra comma. Test writers love to drop a comma between a subject and its verb, especially when the subject is long: The tall stack of library books that had been sitting by the window, finally toppled over. Your ear may want to pause there because the subject is long, but a pause is not a punctuation rule. Cut the comma.
The second trap is a set of answer choices that differ only in where the commas sit. When that happens, the question is purely about structure, so stop reading for meaning and start looking for clause boundaries. Knowing the difference between independent and dependent clauses turns most of these into quick, mechanical decisions. It also helps that each English item on the enhanced ACT comes with an explicit question stem, so you can see up front when a question is about punctuation.
A five-second self-check
When you hit a comma question, ask three things in order. First, is there a complete sentence on each side of the comma? If yes, a comma alone is not enough, and you may be looking at a comma splice. Second, is the comma part of a matching pair around information you could delete? If it opened a pair, it has to close one. Third, if neither is true, does the comma have any job at all? If you can't name the job, delete it.
Drill it until it feels automatic
Commas reward repetition more than almost anything else in the section. Work through short sets of questions, and after each one, say out loud which of the four jobs the comma was doing. thirty-six has concept quizzes built for exactly this kind of focused drilling, so you can hit twenty comma questions in a row instead of stumbling across one every few pages. When commas feel steady, widen out to the full set of ACT punctuation rules and see how the same clause logic shows up with semicolons, colons, and dashes. Remember that there's no penalty for a wrong answer, so even on the ones you're unsure about, make your best call and keep moving.
Start practicing
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This article offers general ACT prep guidance. The ACT can change from year to year, including its format, scoring, policies, test dates, and fees, so always confirm the latest details on the official ACT website at act.org before you make decisions. ACT® is a registered trademark of ACT, Inc. thirty-six is not affiliated with, endorsed by, or sponsored by ACT.