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extrapolate

/ɪkˈstræpəleɪt//ɪkˈstræpəleɪt/·verb
to extend a known trend beyond the data to estimate the unknown
Fig. 1 — Up the ruler beside a young plant, three marks record where its tip stood each week, evenly stepped.
01Definition

To extrapolate is to take the pattern you can already see and carry it past the edge of what you know, in order to estimate what lies beyond. From a few years of sales you extrapolate next year's; from the visible arc of a thrown ball you extrapolate where it will land. The word is built from extra- ('outside') on the model of interpolate, and that contrast is its whole life: interpolating fills a gap between known points, while extrapolating reaches outside their range. Because the pattern is only assumed to hold where no data exists, an extrapolation is a reasoned guess, not a measurement.

02In use
  • iFrom three data points a modeller can extrapolate a trend, then derive a rough forecast for the decade.
  • iiDo not extrapolate national figures from a survey of one small town.
  • iiiEarly results looked strong, but it was reckless to extrapolate a cure from a single trial.
03Collocations
  • extrapolate from the data
  • extrapolate a trend
  • extrapolate into the future
  • dangerous to extrapolate
  • extrapolate beyond the range

Family extrapolation (noun) · extrapolated (adjective)

04Relations

=infer, project, generalize, predict, estimate

≠interpolate

06TOEFL & IELTS

A precise research verb both exams reward in data and science contexts. If a Task 1 chart already shows a projected or dotted trend, you can describe where it is heading — but do not project beyond the data the chart actually gives, since Task 1 marks accurate reporting, not your own forecasts. TOEFL reading passages use it for inference stretched past the evidence. Mind the stress — ik-STRAP-uh-late, not 'EXTRA-polate' — and keep it apart from interpolate: interpolate estimates between known points, extrapolate beyond them.

07Asked
What does extrapolate mean?
To extrapolate is to extend a known pattern beyond the data you have, to estimate what lies past its edge. From the visible part of a trend you reach into the unmeasured part — as in the scene above, where the steady spacing of a plant's weekly marks is carried past the last one, and a dashed line is set at a height nothing has measured yet. It is a reasoned projection, not a certainty, because the pattern is only assumed to continue.
What is the difference between extrapolate and interpolate?
Both estimate unknown values from known ones; the difference is where. Interpolate fills a gap between points you already have — reading a value that sits inside the measured range. Extrapolate reaches outside that range, projecting past the last known point. Guessing a temperature at 2:30 from readings at 2:00 and 3:00 is interpolating; guessing next year's from this year's is extrapolating, and riskier because nothing beyond the data confirms the pattern holds.
What does extrapolate mean in research or data?
It is the move from the tested to the untested — projecting a finding beyond your sample or measured range to conditions you never observed. A drug trialled on adults and extrapolated to children, or a dose-response curve read past its highest tested dose, are both extrapolations. It is how results get stretched to new populations or ranges, which is exactly why careful studies spell out the limits of the data they were built on.
How do you pronounce extrapolate?
ik-STRAP-uh-layt, /ɪkˈstræpəleɪt/, with the stress on the second syllable — STRAP. The common mistake is to say 'EXTRA-polate', hearing the everyday word extra at the front, but the beat falls on -strap-, not -ex-. The noun extrapolation moves the stress again, to the fourth syllable: ik-strap-uh-LAY-shun.
Why is extrapolation considered risky or unreliable?
Because it assumes the pattern you measured keeps holding where you have no measurements — and patterns often bend, level off, or reverse just outside the tested range. A straight line drawn on early data can shoot to absurd values if pushed far enough. This is why 'do not extrapolate too far beyond the data' is a standard caution: the further past the last known point you reach, the thinner the ground under the estimate.
What is the noun form of extrapolate?
Extrapolation — 'an extrapolation from current trends', 'linear extrapolation'. It names both the act of extending the data and the resulting estimate. The adjective extrapolated describes the projected value itself ('the extrapolated figure'). In careful writing the noun usually travels with a hedge — 'a rough extrapolation', 'a crude extrapolation suggests' — because the word itself admits the estimate is uncertain.