Grammar is one of the four criteria you are marked on in both the Writing and Speaking tests. In the Writing test, grammatical range and accuracy account for 25% of your score. That means even if your ideas are excellent and your vocabulary is strong, grammatical errors can hold you back from the band score you need.
In this guide, I will cover the most common grammar mistakes that IELTS candidates make and show you how to avoid them.
Mistake 1: Subject-Verb Agreement
This is one of the most common errors in IELTS writing. The subject and verb of a sentence must agree in number — singular subjects take singular verbs, and plural subjects take plural verbs.
Incorrect: “The number of students have increased significantly.”
Correct: “The number of students has increased significantly.”
The subject here is “the number” (singular), not “students” (plural). This is a common trap because “students” is closer to the verb, but it is not the subject.
Incorrect: “People who lives in cities often face pollution.”
Correct: “People who live in cities often face pollution.”
Here, the relative pronoun “who” refers to “people” (plural), so the verb must be plural.
Mistake 2: Article Errors
Articles (a, an, the) are a persistent problem for many candidates, especially those whose first language does not have articles. Here are the basic rules:
Use “a/an” for singular countable nouns when you are talking about something for the first time or when it is one of many. “A government should invest in education.”
Use “the” when you are talking about something specific or something that has already been mentioned. “The government should invest in education” (referring to a specific government).
Use no article for plural nouns and uncountable nouns when you are talking in general. “Education is important” (not “The education is important”).
Mistake 3: Sentence Fragments
A sentence fragment is an incomplete sentence — it is missing a subject, a verb, or both. In IELTS writing, fragments often occur when candidates try to write complex sentences and lose track of the structure.
Incorrect: “Because the government should invest more in education. This would benefit society as a whole.”
Correct: “Because the government should invest more in education, this would benefit society as a whole.”
Or better: “The government should invest more in education because this would benefit society as a whole.”
Mistake 4: Run-On Sentences
A run-on sentence is two or more complete sentences joined without proper punctuation or conjunctions. This is the opposite of a fragment.
Incorrect: “The population is increasing this causes many problems.”
Correct: “The population is increasing, and this causes many problems.”
Or: “The population is increasing. This causes many problems.”
Or: “The increasing population causes many problems.”
Mistake 5: Incorrect Use of Tenses
Using the wrong tense is a common error, especially when describing trends in Task 1 or discussing past and present in Task 2.
Incorrect: “In 2000, the number of cars has increased.”
Correct: “In 2000, the number of cars increased.”
Use the past simple for completed actions in the past. Use the present perfect for actions that started in the past and continue to the present. Use the present simple for general truths and current situations.
Mistake 6: Confusing Similar Words
English has many words that look or sound similar but have different meanings. Here are some common confusions:
Affect vs Effect: “Affect” is usually a verb meaning to influence. “Effect” is usually a noun meaning a result. “Pollution affects health” (verb). “Pollution has a negative effect on health” (noun).
Economic vs Economical: “Economic” relates to the economy. “Economical” means good value for money. “The economic situation” (correct). “An economical car” (correct).
Principle vs Principal: “Principle” is a rule or belief. “Principal” means main or most important. “The principal reason” (correct). “Moral principles” (correct).
How to Improve Your Grammar
Read widely. The best way to internalise correct grammar is to read high-quality English. Pay attention to sentence structure, article usage, and tense choices.
Write regularly. Write something in English every day — even just a few sentences. The more you write, the more natural correct grammar will feel.
Get feedback. Have a teacher or a native speaker check your writing and point out your most common errors. Focus on fixing one or two errors at a time rather than trying to fix everything at once.
Learn from your mistakes. Keep a record of the errors you make most often. Review this record regularly and make a conscious effort to avoid these errors in your writing.
Grammar is not about memorising rules — it is about developing a feel for the language. With consistent practice and attention to detail, you can significantly improve your grammatical accuracy and boost your IELTS Writing score. Good luck!
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