The main rule

A question tag is a short question added to the end of a statement. The rule is simple:

Positive statement + negative tag?
"It's warm today, isn't it?"

Negative statement + positive tag?
"She can't drive, can she?"

The tag uses the same auxiliary verb as the main sentence (or do/does/did if there is no auxiliary). The subject of the tag is always a pronoun.

Question tag auxiliaries

StatementTagExample
is / am / areisn't / aren'tShe's a doctor, isn't she?
was / werewasn't / weren'tIt was cold, wasn't it?
do / doesdon't / doesn'tYou know her, don't you?
diddidn'tThey won, didn't they?
will / won'twon't / willYou'll help, won't you?
can / can'tcan't / canShe can swim, can't she?
have / hashaven't / hasn'tHe's left, hasn't he?
wouldwouldn'tYou'd like some, wouldn't you?
mustmustn't / don'tWe must leave, mustn't we?

Special cases

CaseExample
I am → aren't I? I'm late, aren't I? (not "amn't I")
There is/are → isn't/aren't there? There's a problem, isn't there?
Imperatives (requests) → will you? / won't you? Open the door, will you? · Have a seat, won't you?
Nobody / nothing → they/it? Nobody called, did they? · Nothing happened, did it?
Let's → shall we? Let's go, shall we?
Intonation matters: Falling intonation (↘) on the tag = you expect agreement: "Nice day, isn't it↘?" Rising intonation (↗) on the tag = genuinely asking / not sure: "You've met her, haven't you↗?"

Exercises

Choose the correct question tag.

1. She works in London, ___?

2. They haven't finished yet, ___?

3. It was a great party, ___?

4. I'm next, ___?

5. Let's take a break, ___?