Is this the correct usage of a comma?

Question

The parties were living together until 3/24/20, which is when Janet moved out.

Is the comma used correctly here?

DW256 · Answer

Yes, it's used correctly.

which is when Janet moved out is a supplementary relative, not an integrated, as it doesn't help to define 3/24/20.

The comma works to separate it prosodically from the rest of the sentence indicating a slight pause in speech.

In writing, the comma serves to mark the fact that the relative is not a modifier of the noun phrase it takes as its antecedent, but a supplement.

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