Can "Once in a Blue Moon" Hurt Your IELTS Speaking Score?
Using “once in a blue moon” the wrong way can keep you at band 6. See what it means, why examiners notice it, and how to use it for a higher score.
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Can "Once in a Blue Moon" Hurt Your IELTS Speaking Score?
Today another student asked me, "Can I just use 'once in a blue moon' as my idiom for IELTS speaking?" The short answer is yes, but there's a catch. It is a real idiom, but using it too generically can actually hurt your score. Let's look at what it means, why so many students use it, and how to use it in a way that impresses the examiner.
What Does "Once in a Blue Moon" Mean?
"Once in a blue moon" means not often, or very rarely. You can easily replace it with "once in a while" or "rarely."
Why Do People Say It?
A blue moon is a rare event in the sky, so it doesn't happen often. When we say something happens "once in a blue moon," we mean it only happens on very rare occasions, just like that moon. The image makes the idiom easy to remember and easy to use, and that's exactly why so many IELTS students rely on it.
When Can You Use "Once in a Blue Moon"?
When describing something you do very rarely, like exercising early or eating out
When talking about rare events, like seeing an old friend
When you want to replace "rarely" or "not very often" with something more natural
In IELTS speaking, but only when it fits the answer naturally
Why Can It Hurt Your IELTS Score?
Because the idiom is so simple, too many students use it freely, and examiners notice. When the same idiom appears in answer after answer, the examiner starts to wonder: is this student really comfortable in English, or just using a memorized phrase?
Here's an example of how it can go wrong.
Examiner: "What do you usually do in the morning?"
Student: "Once in a blue moon in the morning I will wake up early and take a walk or do some exercise."
This answer isn't wrong, and the idiom is used correctly. But it sounds like a mental template, a memorized opening that could be used for almost any question. When an idiom can be dropped into most answers, it doesn't show real English ability. An answer like this usually reflects a band 6.
How to Use It the Right Way
Now let's use the same idiom, but properly.
Student: "Well, I usually don't do much in the morning except take a shower and eat a healthy breakfast. But once in a blue moon, I might wake up extra early and force myself to go for a run."
Do you notice the difference? The idiom now fits naturally into a real, complete answer. It compares a normal routine with a rare exception, so it actually makes sense in context. This is the kind of answer that can reach band 7 or higher.
Try reading both answers out loud a few times. After a few tries, I'm sure you'll hear the difference yourself!
Business English Example
A manager explains how often the team meets in person: "We usually work remotely, but once in a blue moon, we get everyone together in the office for a big planning session."
Everyday English Example
A friend asks if you watch TV often: "Not really. Once in a blue moon I'll binge a series on the weekend, but mostly I'm too busy."
Vocabulary and Expressions
Generically — in a general way that fits many situations, without real detail Example: He answered the question generically, so it didn't sound personal.
Proficient — skilled and comfortable at doing something Example: She is proficient in English and speaks with confidence.
Template — a fixed pattern you copy and reuse Example: Using the same template for every answer sounds memorized.
💡 Teacher's Tip
Don't treat an idiom as a decoration you add to the start of every answer. Use it when it truly fits your story, and give it a contrast or a reason, like "I usually do X, but once in a blue moon I do Y." That small structure makes your English sound natural, not memorized.
Practice
1. What does "once in a blue moon" mean?
A) Very often
B) At night only
C) Every full moon
D) Very rarely
2. Which answer uses "once in a blue moon" in the most natural way for IELTS?
A) I usually take the bus to work, but once in a blue moon I'll cycle if the weather is perfect.
B) Once in a blue moon, I like my job.
C) Once in a blue moon is my favorite idiom, so I use it here.
D) Once in a blue moon, yes.
Answers: 1) D 2) A
Build Your English Habit
This week, try using "once in a blue moon" in a full, natural sentence with a contrast, like the run example above. Then record yourself and listen back. If it sounds like a template, rewrite it until it sounds like you. Small improvements like this build real confidence for the speaking test.
✦ Go slow. Go fast. Just keep going.