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Extrapolation - GCSE Maths Definition

Reviewed by: Mark Curtis

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What is extrapolation?

In GCSE Maths, extrapolation means extending a line of best fit on a scatter graph beyond the region of points plotted on the scatter graph, then using the extended line of best fit to predict values. It should not be confused with interpolation, which is using the line of best fit to predict values within the regions of points plotted on the scatter graph.

Graph showing a blue best-fit line with extrapolation and interpolation areas marked. Interpolation is between x=1-7; extrapolation extends beyond x=7.
A line of best fit being used for interpolation (blue) and extrapolation (red).

Extrapolation is often unreliable, as you don’t know if the linear relationship between the two variables will continue beyond the set of data given. The further you extrapolate, the less reliable the estimates become!

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Mark Curtis

Reviewer: Mark Curtis

Expertise: Maths Content Creator

Mark graduated twice from the University of Oxford: once in 2009 with a First in Mathematics, then again in 2013 with a PhD (DPhil) in Mathematics. He has had nine successful years as a secondary school teacher, specialising in A-Level Further Maths and running extension classes for Oxbridge Maths applicants. Alongside his teaching, he has written five internal textbooks, introduced new spiralling school curriculums and trained other Maths teachers through outreach programmes.

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