How long should a conclusion be?

The 5–10% guideline — where it comes from

Conclusions run shorter than introductions because their job is smaller: no orientation needed, no question to set up — just the argument's landing. For a 1,500-word essay that's 75–150 words; for a 3,000-word paper, 150–300.

A conclusion that balloons past 10% is usually doing forbidden work: introducing new evidence, starting a fresh argument, or re-summarizing every section in order. If a point matters, it belongs in the body; the conclusion states what the body earned.

The 5–10% figure is a DESCRIPTIVE convention from academic writing guidance (university writing centres such as Harvard's and Purdue's, and editing guides like Scribbr, as of 2025) — Harvard is explicit that there is no single right answer: discipline and the paper's own path decide what the conclusion must do. Document types differ systematically: essays sit near the middle of the band, research papers push the top because the conclusion carries implications and limitations, and business reports often run shorter because a separate executive summary does the closing work. When a brief or rubric names a length, it beats any percentage.

What a conclusion actually does

Two moves, occasionally three: restate the thesis in the light of the evidence presented (not verbatim), state the answer's significance — why it matters beyond this essay — and, where the genre allows, one forward-looking sentence: a limitation, an open question, an implication.

The weakest conclusions start "In conclusion" and repeat the introduction with synonyms. Markers read hundreds of those; landing the significance instead is what separates strong finishes.

A worked structure (anonymized)

A 2,000-word literature essay closed in 138 words — about 7%: one sentence returning to the question (the «what»), two tying the argument's strands together, two on why the reading matters beyond the text (the «so what»), one closing line. Nothing new — no fresh quotation, no evidence the body hadn't earned. The strongest conclusions spend their words on significance, not summary.

That shape scales: a 500-word essay's conclusion does each job in a clause; an 8,000-word paper expands the «so what» into implications and limitations.

Can a conclusion be one sentence?

In short-form writing, yes — a decisive closing line can outperform a paragraph. In academic essays a single-sentence conclusion reads as abrupt; aim for at least 3–4 sentences that restate, contextualize and close.

Should the conclusion repeat the introduction?

It should mirror the introduction's promise, not repeat its words. The introduction says what you'll argue; the conclusion says what the argument established and why it matters — informed by everything between.

Is the 5–10% rule a real rule?

No — it's a convention that describes what most academic conclusions end up at, not a requirement anyone enforces. Harvard's writing centre explicitly declines to give one right answer; disciplines, formats and briefs override any percentage. Reports with executive summaries often close shorter; reflective essays sometimes longer. If your rubric names a length or structure, follow that.

Can I introduce new evidence in the conclusion?

No — a conclusion ties together what the body established and says why it matters. A new quotation or data point raises questions the essay no longer has room to answer; markers read it as a structural error. If the evidence matters, it belongs in the body.