How to Write Complex Sentences for IELTS Writing (Band 7 Grammar)

Of the four criteria that make up your IELTS Writing score, Grammatical Range and Accuracy is worth a full 25% — and it is the one where candidates most often plateau at Band 6. The descriptors are specific: Band 6 allows "a mix of simple and complex sentence forms" with errors that rarely block meaning, while Band 7 demands "a variety of complex structures" together with "frequent error-free sentences." In other words, the jump is not about writing longer sentences. It is about controlling a wider range of structures accurately. This guide shows you the four complex sentence types examiners look for, how to build each one correctly, and the mistakes that quietly cost the band.

What "complex" actually means

A complex sentence is simply one main clause joined to at least one subordinate (dependent) clause. It is not a long sentence, a fancy sentence, or one stuffed with linking words. "Because prices rose, demand fell" is complex; "Prices rose and demand fell, therefore, in addition, the market changed" is just a simple idea buried in connectors. Examiners reward structural variety and accuracy — not word count — so your goal is a natural mixture of sentence types where most sentences contain no errors.

The four complex structures that raise your band

1. Relative clauses

Relative clauses add detail using who, which, that, whose, or where. They let you combine two facts into one controlled sentence:

• Simple: Governments fund public transport. It reduces congestion.
• Complex: Governments fund public transport, which reduces congestion.

Use a comma before which when the clause adds extra, non-essential information (a non-defining clause). Do not use commas — and do not use which for people — when the clause identifies who or what you mean: "Students who study abroad often adapt quickly."

2. Conditional sentences

Conditionals are ideal for Task 2 because they let you argue about cause, consequence and hypotheses. The two most useful in essays are:

• First conditional (real future): "If governments raise fuel taxes, drivers will use cars less."
• Second conditional (hypothetical): "If university were free, more students would enrol."

Keep the tenses consistent: a common Band 6 error is mixing them ("If governments would raise taxes, drivers use cars less"). Match the pattern exactly and the sentence stays accurate.

3. Adverbial (subordinate) clauses

These open with a subordinating conjunction — although, because, while, whereas, since, unless, as, when — and are the workhorse of a good essay. They express contrast, reason, time and condition in one clause:

• Contrast: "Although remote work saves commuting time, it can weaken team communication."
• Reason: "Air quality improved because fewer vehicles entered the city centre."
• Comparison: "Older employees value job security, whereas younger workers prioritise flexibility."

A powerful trick for variety is to move the clause to the front and add a comma, so your sentences do not all begin with the subject: "Because fewer vehicles entered the centre, air quality improved."

4. Participle clauses

These begin with an -ing or -ed form and are the structure that most clearly signals Band 7+ control: "Faced with rising costs, many families reduce spending." or "Governments should invest in renewables, reducing long-term emissions." The subject of the participle must match the subject of the main clause — otherwise you create a "dangling" modifier, so use these carefully and check that the doer is clear.

Common mistakes that cancel the benefit

Reaching for complex sentences is exactly when accuracy tends to slip. Watch for these:

1. Comma splices: joining two full clauses with only a comma ("Cars cause pollution, they should be taxed"). Use a full stop, a semicolon, or a conjunction such as so.
2. Run-on sentences: three or four clauses chained together until the reader loses the thread. If you cannot say it aloud in one breath, split it.
3. Double conjunctions: "Although it is expensive, but it is effective." English uses one, not both.
4. Every sentence the same shape: if all your sentences start with the subject, vary the openings using front-position adverbial and participle clauses.

For a fuller list of the accuracy errors examiners see most, see our guide to the most common grammar mistakes in IELTS Writing.

A three-step plan to build the skill

1. Combine, don't lengthen. Take two short sentences from any practice answer and join them with a relative, conditional, or adverbial clause. Do this ten times a day.
2. Vary your openings. In each body paragraph, deliberately start one sentence with a subordinate clause and one with a participle. Variety of sentence starts is part of "range."
3. Proofread for boundaries. Reserve the last three minutes of each task to check one thing only: where one clause ends and the next begins. This catches most comma splices and run-ons.

Check your grammar before test day

Because Grammatical Range and Accuracy is scored on real writing, the fastest way to improve is to see which errors you personally repeat. Our free AI writing checker gives detailed feedback on a full essay — note that the free tier is a single lifetime sample report, so save it for an essay you have written under timed conditions. Once you have an estimated Writing band, use the free band score calculator to see how it combines with your Reading, Listening and Speaking into an overall score. Fix the two error types you repeat most, add one new complex structure to your toolkit each week, and the grammar band tends to look after itself.