Does a comma go before "since"? The short answer is: it depends on the structure of your sentence. "Since" can act as a subordinating conjunction introducing a time clause or a reason clause, and the comma rule shifts depending on whether that clause opens the sentence or closes it. Once you see the pattern, the decision takes about two seconds.
What "since" actually does in a sentence
"Since" carries two distinct meanings in English. First, it marks a point in time: "She has worked here since 2019." Second, it signals a reason, functioning much like "because": "Since the report is ready, we can proceed." Both meanings are standard in professional writing. The comma rule applies to both in the same way, so you don't need to worry about which meaning is in play.
The word "since" introduces a dependent clause. A dependent clause can't stand on its own as a sentence. That fact is the key to understanding where the comma goes.
When you don't need a comma before "since"
Skip the comma when the "since" clause comes at the end of the sentence, after the main clause.
- "The team has used the new system since January."
- "Revenue has grown since the restructure took effect."
- "She hasn't replied since I sent the proposal."
In each case, the main clause comes first and the "since" clause follows. No comma is needed. Adding one would interrupt a natural flow that the reader's eye doesn't need help navigating.
This is the most common structure in business writing, so in practice you'll omit the comma more often than you'll include it.
When you do need a comma after "since"
Use a comma when the "since" clause opens the sentence. The dependent clause comes first, the main clause follows, and a comma separates them.
- "Since the deadline has moved, we need to revise the schedule."
- "Since 2020, the company has doubled its client base."
- "Since you asked, here's the full breakdown."
The comma here is doing real work. It tells the reader that the introductory clause has ended and the main statement is starting. Without it, the sentence can stall while the reader works out where one thought ends and the next begins.
This rule applies broadly to using commas with introductory clauses and phrases. "Since" is simply one of the conjunctions that triggers it.
A comma before "since" in the middle of a sentence
Sometimes writers place a "since" clause in the middle of a sentence, bracketed by commas. This is less common in business writing but grammatically fine when the clause is genuinely parenthetical.
"The proposal, since it covers three departments, will need sign-off from each head." Here both commas are required because the "since" clause interrupts the main clause. Remove it and the sentence still stands: "The proposal will need sign-off from each head."
If the "since" clause is not interruptive, don't add mid-sentence commas. Write the sentence so the clause lands at the front or back instead. Restructuring is almost always cleaner than parenthetical insertion.
Common mistakes to avoid
The most frequent error is adding a comma before "since" at the end of a sentence. "Revenue has grown, since the restructure took effect" is wrong. The comma suggests a pause that the sentence doesn't need and doesn't earn.
The second error is omitting the comma when "since" opens the sentence. "Since the deadline has moved we need to revise the schedule" makes the reader work harder than necessary. The comma after "moved" costs nothing and saves a beat of confusion.
A third mistake is confusing "since" with "because" and treating them as interchangeable in every context. They're close in meaning when signaling a reason, but "since" carries a mild implication that the reason is already known to the reader. Use "because" when the reason is new information or when you want no ambiguity. The comma rule is the same for both, so this is a tone question, not a punctuation one.
How this connects to the broader comma-before-conjunction question
"Since" is a subordinating conjunction, not a coordinating one. Coordinating conjunctions (and, but, or, nor, for, yet, so) follow a different comma rule: they take a comma before them when joining two independent clauses. Subordinating conjunctions like "since," "because," "although," and "when" don't take a comma before them in end position. They do take a comma after them in opening position.
If you've already worked through the rules for using a comma before and after "but", you'll recognize the underlying logic. The junction type determines the rule.
Keep this distinction clear and you'll handle most comma decisions without stopping to second-guess yourself. The test is always the same: where does the dependent clause sit? Front gets a comma after it. End gets none.
Quick reference
"Since" clause at the end: no comma. "The project has run smoothly since the kickoff meeting."
"Since" clause at the front: comma after the clause. "Since the kickoff meeting, the project has run smoothly."
"Since" clause in the middle (parenthetical): commas on both sides. "The project, since the kickoff meeting, has run smoothly."
One word, three positions, and a consistent logic behind each. That's the full rule.