Rule 1: If “once” acts as an adverb, you should use a comma.
For these sentences, “once” means “on one occasion.”
- Correct: Once, I went to Paris with my wife.
- Incorrect: Once I went to Paris with my wife.
Rule 2: If “once” is used to mean “when” or “as soon as,” you do not need to use a comma.
For these sentences, “once” can appear at the start or in the middle of the sentence.
- Correct: Send me a message once you get there, so I know you arrived safely.
- Incorrect: Send me a message once, you get there, so I know you arrived safely.
Rule 3: When the word “once” forms part of a “once phrase,” you should not use a comma after “once.”
However, you should use a comma at the end of the phrase.
- Correct: Once upon a time, there was a big bad wolf.
- Incorrect: Once, upon a time, there was a big bad wolf.
Keep reading so you can learn more about the different rules regarding “once” and see more examples of when to include or omit the comma.
When to Use a Comma After “Once”
When deciding whether to use a comma after “once,” please see Rule 1.
Rule 1: Use a comma after “once” when you use it to mean “on one occasion.”
These sentences always refer to the past, and “once” is similar to saying, “One time, this happened…”
The word “once” can appear at the start of the sentence or the end of a clause.
- Once, I left the house still wearing my slippers.
- She said she had been there once, but she couldn’t remember how to get there.
When to Avoid a Comma After “Once”
On most occasions, it is not necessary to put a comma after “once.” However, the following two rules explain precisely when you do not need a comma after “once.”
Rule 2: You shouldn’t use a comma after “once” when you use it to mean “when” or “as soon as.”
On these occasions, “once” appears at the start or the middle of the sentence and is never followed by a comma.
- She said that once she got there, she would call.
- Once I see him, I will tell him what I think of his plan.
Rule 3: You shouldn’t use a comma after “once” when it forms part of a “once clause” or “once phrase.”
Once clauses are short phrases in which the other words of the phrase are essential to the meaning of “once.”
On these occasions, you should not put the comma after “once,” but you do need to use a comma after the phrase itself.
- Once upon a time, there was a beautiful princess.
- Once again, he has let us all down.
- Once in a while, I like to walk alone on the beach.
Conclusion
Use a comma after “once” when it means “on one occasion.” However, if “once” means “when” or “as soon as,” you do not need a comma. Furthermore, in “once phrases” such as “once upon a time,” the comma is at the end of the phrase, not after the word “once.”