Did Donald Knuth say "Premature optimization is the root of all evil"?

Q: Did Donald Knuth say "Premature optimization is the root of all evil"?

Yes. Knuth wrote the line, in these exact words, in "Structured Programming with go to Statements," published in ACM Computing Surveys in December 1974 — it sits on page 268 of the scanned paper. What almost never travels with it is the sentence that follows, in which Knuth insists the critical 3 of code should be optimized.

Who really said it

Premature optimization is the root of all evil

Written by Donald Knuth Born 1938 · American computer scientist · 1974 Turing Award

Verified In copyright

Knuth wrote the line, in these exact words, in “Structured Programming with go to Statements,” published in ACM Computing Surveys in December 1974 — it sits on page 268 of the scanned paper. What almost never travels with it is the sentence that follows, in which Knuth insists the critical 3% of code should be optimized.

Last verified 22 Jul 2026 · how we verify · spot an error?

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Verified quote & credit

“Premature optimization is the root of all evil” Donald Knuth, "Structured Programming with go to Statements," ACM Computing Surveys 6, no. 4 (December 1974): 261–301, at 268. Verified by Quotle.info.

Can you use it?

Still under copyright (rights held by Donald E. Knuth and the Association for Computing Machinery (publisher of Computing Surveys)). A short, credited quote is generally fine for talks, teaching, and internal decks; for commercial, published, or large-scale reuse, get permission.

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In context

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Provenance

The source, confirmed

Work: Structured Programming with go to Statements
Published: ACM Computing Surveys 6, no. 4 (December 1974): 261–301
Page: 268
Also in: “Computer Programming as an Art,” Communications of the ACM 17, no. 12 (December 1974) — a hedged variant

We should forget about small efficiencies, say about 97% of the time: premature optimization is the root of all evil. Yet we should not pass up our opportunities in that critical 3%. Excerpt

Quoted from page 268 of the scanned paper. The preceding sentences describe programmers wasting time on the speed of noncritical code; the following ones urge close attention to critical code — but only after it has been identified.

Read the 1974 paper (scan, PDF)

How we verified this

The exact sentence appears on page 268 of the December 1974 Computing Surveys paper — confirmed in the full scan ↗, under the running head “268 • Donald E. Knuth.”
Knuth used a softer version the same year in his Turing Award lecture, adding the qualifier “(or at least most of it) in programming” — visible in the archived lecture text ↗.
Wikiquote’s sourced entry ↗ carries both 1974 wordings and notes that Knuth called the saying “Hoare’s Dictum” in his 1989 paper “The Errors of TeX,” adding that the attribution to Hoare is doubtful.
Hoare, asked about it in 2004, said he had no recollection of how the quotation came about — reproduced in this provenance write-up ↗.

In copyright

This is a 1974 journal article, so it is well inside the term of US copyright — nothing here is public domain. The short excerpt above is reproduced for identification and verification, with full citation; longer reuse should go through the ACM or the author.

Rights status is our research, not legal advice — and copyright varies by country and edition. For commercial or published use, confirm with the rightsholder. See terms.

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Fact-check

The credit that keeps going to the wrong man

This one is unusual: the quote is genuine, the author is famous, and the misattribution was started by the author himself.

C. A. R. Hoare Doubtful

In his 1989 paper “The Errors of TeX” Knuth referred to the saying as Hoare’s dictum — apparently having forgotten he wrote it. Wikiquote records that reference and states plainly that the attribution to Hoare is doubtful ↗.

Edsger W. Dijkstra Unsupported

Asked in 2004 where the line came from, Hoare replied that he had no recollection of it and guessed he might himself have credited Dijkstra — a guess, not a source, as the provenance write-up documents ↗.

Donald Knuth (truncated) Mis-worded

The sentence is almost always quoted alone. In the 1974 paper ↗ it is preceded by “say about 97% of the time” and followed immediately by a warning not to pass up the critical 3%.

Knuth wrote it, in December 1974, on page 268 of “Structured Programming with go to Statements” ↗ — and then, in 1989, credited it to someone else.

Context

Why the missing half matters

Knuth was not telling programmers to stop caring about speed. The paragraph the line comes from is an argument for efficiency — he opens it by complaining that people were then “condemning program efficiency,” and he ends it by insisting the genuinely hot 3% of a program deserves careful attention, once you have measured which 3% it is. The famous sentence is the middle of a sandwich, served without its bread.

The same 1974 essay is where Knuth reports his own measurements of where programs actually spend their time, which is why the “97% / 3%” framing is not rhetorical decoration. Strip it away and the aphorism flips from “measure first” into “never optimize” — a reading Knuth spends the surrounding pages arguing against.

The quote is real. The version most people carry around is missing the half that makes it advice.

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More provenance-checked quotes on the same theme, each with its reuse status.

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Go further

Dig deeper

Trusted places to keep pulling the thread — primary archives, fact-checks, and scholarship. We show how we used each one before you leave.

Donald Knuth — Wikiquoteen.wikiquote.org

Sourced entry for both 1974 wordings, with the footnote that Knuth later called it “Hoare’s Dictum” and that the Hoare attribution is doubtful.

“Structured Programming with go to Statements” (1974 scan)pic.plover.com

Full scan of the Computing Surveys paper; the sentence appears on page 268.

“Computer Programming as an Art” (Turing lecture scan)cs.tufts.edu

Knuth’s 1974 Turing Award lecture, containing the hedged variant with “(or at least most of it) in programming.”

“Premature optimization is the root of all evil” — The Lumber Roomshreevatsa.wordpress.com

The standard provenance write-up: both 1974 citations, Knuth’s 1989 misattribution, and Hoare’s 2004 email disclaiming the line.

C. A. R. Hoare — Wikiquoteen.wikiquote.org

Lists the saying among quotes credited to Hoare while noting the quote is due to Knuth and the Hoare attribution is doubtful.

Donald Knuth — Wikipediaen.wikipedia.org

Biography: born 10 January 1938, Stanford professor emeritus, 1974 Turing Award.

The true author

Who was Donald Knuth?

Donald Knuth

Born 1938 · American computer scientist · Stanford professor emeritus

Donald Ervin Knuth (born 10 January 1938) is an American computer scientist and professor emeritus at Stanford University, best known for the multi-volume The Art of Computer Programming and for creating the TeX typesetting system. He received the ACM Turing Award in 1974 — the same year he published both texts in which this sentence appears. Knuth is a meticulous citer of sources, which makes the central irony here delicious: the one attribution he got wrong was his own.

For writers & researchers

Cite this

Cite this source

Knuth, Donald E. “Structured Programming with go to Statements.” ACM Computing Surveys 6, no. 4 (December 1974): 261–301, at 268.

This verification page

Quotle.info. “Who really said ‘Premature optimization is the root of all evil’?” Last verified 22 Jul 2026. https://quotle.info/who-said/premature-optimization-is-the-root-of-all-evil/