Comma rules

The comma is the most used and most misused punctuation mark. You do not need every rule — the handful below covers most everyday writing.

What it is

A comma is a small pause or a separator. It is not a "get tired, pause" mark; it signals structure within a sentence.

The main uses

To separate items in a list. "I bought bread, milk, and eggs." (Whether to include the last comma before "and" depends on style — see the note below — but most style guides advise the serial comma.)

To separate two full clauses joined by and, but, yet, or, so. "She read the brief, and then she wrote the reply." The comma goes before the conjunction.

After an introductory word or phrase. "After the meeting, we reviewed the notes." "However, the plan changed."

Around extra information (a non-essential clause). "My sister, who lives in Lagos, called yesterday." The commas mark information you could remove and keep the sentence complete.

To separate two adjectives of the same kind. "A long, tedious report." (Only if "and" could go between them.)

In dates and addresses. "On 3 September 2026, the office opened."

Step-by-step guide

Read the sentence aloud. If you naturally pause, a comma may belong there — but always confirm against a rule.

Identify the clause. If the comma separates a full clause (subject + verb), you likely need the conjunction too.

Check whether the extra phrase can be removed. If it can, wrap it in commas; if it cannot, use no commas.

Be sparing. Too many commas make writing choppy. When in doubt, prefer a short sentence or a period over a comma salad.

Common comma mistakes

The comma splice. Two full sentences joined by only a comma: "The report was ready, it was sent to the client." This is a run-on. Fix by adding a conjunction, using a semicolon, or splitting into two sentences.

Missing comma after an intro. "After the meeting the notes were shared" is clearer as "After the meeting, the notes were shared."

Commas where they are not needed. Putting a comma between a subject and its verb, or before "that."

The serial comma debate. Some styles (Oxford) use it, some do not. Pick one and be consistent within a document.

Practical tips

• When you have used three or more commas in a sentence, rewrite it.
• If two commas are not separating a removable phrase, check that they are needed.
• Consistency matters more than which rule you follow.

Checklist

• I separated list items correctly.
• I used a comma before the conjunction in compound sentences.
• I added a comma after introductory phrases.
• I wrapped removable information in commas.
• No comma splices.
• I used commas sparingly and consistently.