A question tag is a short check you add to the end of a sentence, to ask the other person to confirm it. Find the helping word (a form of be, or have, will, can…), flip it, and add it back: a positive sentence gets a negative tag.
Not "You're tired, are you?" — say "You're tired, aren't you?". A positive sentence takes a negative tag: aren't you, not "are you".
Try it: She is a teacher. Add the right tag. (Leave out the word you don't need.) Answer: She is a teacher, isn't she? — The sentence is positive (She is), so the tag is negative: isn't she? "Is she?" would repeat the positive instead of flipping it, so it's left out. A positive sentence takes a negative tag.
Negative sentence, positive tag
Flip it the other way too: a negative sentence gets a positive tag. Same helping word, flipped.
You aren't tired. → You aren't tired, are you?
He didn't call. → He didn't call, did he?
She can't drive. → She can't drive, can she?
Try it: He didn't call. Add the right tag. (Leave out the word you don't need.) Answer: He didn't call, did he? — The sentence is negative (didn't call), so the tag is positive: did he? "Didn't he?" would repeat the negative instead of flipping it, so it's left out. A negative sentence takes a positive tag.
No helping word? Use do / does / did
Some sentences have no helping word — just a plain present- or past-simple verb (She likes…, They live…, He left…). There is nothing to flip, so you bring in do, does, or did to build the tag. Match the person and time: does for he/she/it, do for the rest, did for the past.
She likes coffee. → She likes coffee, doesn't she?
They live here. → They live here, don't they?
He left early. → He left early, didn't he?
Not "She likes coffee, isn't she?" — say "She likes coffee, doesn't she?". "Likes" is not a form of be, so the tag can't use isn't. There's no helping word, so bring in does → doesn't she.
Try it: She likes coffee. Add the right tag. There's no helping word, so bring one in. (Leave out the word you don't need.) Answer: She likes coffee, doesn't she? — "Likes" has no helping word and isn't a form of be, so bring in does and flip it: doesn't she? "Isn't" would wrongly treat likes like a be-verb, so it's left out. No helping word → use do/does/did.
Match the helping word you already have
When the sentence already has a helping word — have, will, can, should, or a form of be — the tag reuses that same word, flipped. Don't swap in do/does/did here; only use those when there is no helping word.
They have finished. → They have finished, haven't they?
He will come. → He will come, won't he?
You can swim. → You can swim, can't you?
Try it: They have finished. Add the right tag. Match the helping word. (Leave out the word you don't need.) Answer: They have finished, haven't they? — The sentence uses have, so the tag uses have too, flipped to negative: haven't they? "Didn't" would bring in a different helping word that the sentence doesn't use, so it's left out. Match the helping word, then flip it.