Short answer: idioms belong in IELTS Speaking, not Writing. The Speaking band descriptors refer to idiomatic language directly at band 7 and above; the Writing descriptors never do.
Two or three natural idioms across an 11–14 minute interview is the right amount, and an idiom that makes you pause to retrieve it costs more in Fluency than it earns.
Why idioms help in Speaking and hurt in Writing
At band 7 the Speaking descriptors credit a candidate who "uses some less common and idiomatic vocabulary", with some awareness of style.
Writing Task 2 asks for an academic register, where an idiom is a register mismatch — "the government should pull its socks up" is not band 8 language, it is informal language in a formal task.
So the rule is simple: idioms are a Speaking asset and a Writing liability. If you have limited study time, learn them for the interview and leave them out of the essay entirely.
Where in the interview idioms belong
| Part | Fits? | Why |
|---|---|---|
| Part 1 (short answers on familiar topics) | Rarely | Answers are 2–3 sentences. An idiom in the first minute reads as prepared, because there has been no time for anything else. |
| Part 2 (the long turn) | Yes, one or two | You are telling a story for two minutes, which is where natural figurative language actually occurs. |
| Part 3 (abstract discussion) | Yes, one or two | Discussion invites evaluation, and several natural idioms are evaluative. |
Forty that sound natural
Talking about time and habit
every now and then · once in a blue moon · from time to time · on the spur of the moment · in the long run · around the clock · a matter of time
Talking about difficulty
easier said than done · a steep learning curve · an uphill battle · out of my depth · take its toll · a tall order
Talking about opinions and disagreement
see eye to eye · beg to differ · on the fence · take something with a pinch of salt · have mixed feelings about · there is no denying that
Talking about effort and success
put in the hours · pay off · get to grips with · go the extra mile · pick something up quickly · make headway · get off the ground
Talking about money and cost
cost an arm and a leg · on a shoestring · value for money · make ends meet · tighten our belts
Talking about feelings
over the moon · a weight off my shoulders · in two minds · get on my nerves · miss the point · lose track of time · second nature to me
Twelve that give you away
These are not wrong. They are so heavily taught in coaching centres that examiners hear them dozens of times a week, and using several together is a recognisable pattern rather than evidence of range.
| Over-used | Why it stands out | Natural alternative |
|---|---|---|
| It's a piece of cake | The single most-coached idiom in IELTS preparation. | It's straightforward · I find it easy enough |
| It's raining cats and dogs | Rarely said by fluent speakers, and never in an interview. | It's pouring · it's absolutely tipping down |
| Hit the nail on the head | Appears in every idiom list; almost never fits the question asked. | That's exactly right · that's precisely the issue |
| Once in a blue moon (over-used) | Fine once. Candidates use it for anything infrequent, including things that happen monthly. | Hardly ever · very occasionally |
| Every cloud has a silver lining | A proverb rather than an idiom, and it rarely answers the question. | There was an upside · it worked out in the end |
| Kill two birds with one stone | Extremely over-taught, and often forced into an answer that does not need it. | It solves both problems at once |
| The tip of the iceberg | Common in coaching, and usually over-claims the scale of what is being discussed. | That's only part of it |
| Burn the midnight oil | Dated in most varieties of English. | Stay up late working · put in long nights |
| A blessing in disguise | Fine in principle, but reached for automatically after any negative story. | It turned out to be useful |
| Break the ice | Over-taught and frequently used for situations with no awkwardness in them. | Get the conversation going |
| At the end of the day (as filler) | Natural, but candidates use it three or four times as a stalling device. | Ultimately · on balance — and only once |
| Last but not least | A signposting cliché in both Speaking and Writing. | And finally · the other thing is |
The rule that matters more than the list
Fluency and Coherence is where most band 6 candidates lose their half band, and retrieval pauses are what cost it. If an idiom arrives without effort, use it.
If you have to search for it, the search itself is the more expensive mistake — the descriptors reward speech that is sustained and connected, and hesitation to find language is named explicitly as a limiting feature.
Which means the honest advice is: learn ten idioms properly rather than sixty loosely, and use them only where they fit the question.
You can rehearse that under a clock with the timed Part 2 practice, and get a band per criterion on a full three-part interview with the Speaking test — Fluency is reported separately, which is the only way to see whether your vocabulary is helping or costing you.