IELTS Writing Task 1 Grammar: Trends, Comparisons and Processes

Academic Task 1 asks you to describe a chart, graph, table, or process diagram objectively, and its grammar demands are specific: trend language, comparison, and — for process diagrams — the passive voice. General Training Task 1 is a letter instead, with its own register concerns (formal, semi-formal, or informal openings and closings) that don't overlap much with chart description.

This guide focuses on Academic Task 1, because its grammar is the most technical and rule-bound of any IELTS writing task — get the tense and the trend vocabulary wrong, and the data description becomes factually inaccurate as well as ungrammatical. General Training candidates should read the letter-writing conventions in their task instructions instead of the chart-specific advice below.

Every trend has three grammatical forms worth knowing, because varying between them — rather than repeating the same verb sentence after sentence — is itself a range signal. The verb form carries the main clause ('sales rose steadily'), the noun form pairs with 'a' or 'an' and a describing adjective ('a steady rise in sales'), and the adverb modifies the verb to show speed or size of the change. Examiners notice when a report leans on only one of the three forms for the entire response.

The chart's own time frame decides the tense, not personal preference. If every data point sits in the past — a chart covering 1990 to 2010, for instance — the past simple describes every change: 'Car ownership doubled between 1990 and 2010.' If the chart's final data point is the present moment, or the trend explicitly continues beyond the chart, the present perfect is correct instead: 'Renewable energy use has risen steadily since 2010.'

The present simple appears only for a chart with no time dimension at all — a single snapshot, like a pie chart of current spending categories — where you are stating a fact rather than describing change over time: 'Housing accounts for the largest share of household spending.' Mixing these three inappropriately is one of the most common Task 1 accuracy errors, because it makes the timeline of the data unclear.

• Car ownership has doubled between 1990 and 2010.(the period is entirely finished, so the past simple is required)
• Car ownership doubled between 1990 and 2010.
• Renewable energy use has risen steadily since 2010.(the trend reaches the present, so the present perfect is correct)

Bar and pie charts almost always require comparison between categories, and comparatives and superlatives are the grammar that carries it: 'Spending on housing was higher than spending on transport' compares two categories directly, while 'Housing accounted for the highest proportion of spending' picks out one category from the whole set.

A frequent error is comparing without a clear second term — 'Housing spending was more higher' both doubles the comparative and drops the 'than' clause it needs. Keep the comparison explicit: state both categories, and use 'than' every time you use a comparative adjective, never a superlative.

• Housing spending was more higher than transport spending.('more' and '-er' cannot both mark the comparative)
• Housing spending was higher than transport spending.

Process diagrams describe a sequence of steps — manufacturing, recycling, a natural cycle — where the person or machine performing each step is usually unknown or irrelevant. This is precisely what the passive voice was built for: 'The raw material is transported to the factory, where it is sorted and cleaned' keeps the focus on the material moving through the process, not on an invented worker.

Sequencing language pairs naturally with the passive here — first, next, after this, once X has been done, finally — and the present simple passive is the default tense for a diagram showing a general, repeating process rather than a one-off past event.

• The raw material is transported to the factory, where it is sorted and cleaned.(present simple passive — a general, repeating process)
• Once the water has been filtered, it is stored in a holding tank.

The most frequent Task 1 error is tense mismatch with the chart's time frame — using the present perfect for a chart that ends in the past, or the past simple for one that reaches the present. A close second is a missing or wrong article before a percentage or category name: 'percentage of the population increased' needs 'the percentage' or simply 'the population'.

A third recurring error is overusing 'increase' and 'decrease' as the only trend verbs in the whole report, which flattens the range an examiner is looking for; rotating through the synonyms in the table above, plus varying sentence position (starting with the trend, or with the time period), demonstrates far more control.