Stats & Algebra
Interpolation Calculator
Know two points on a line? Estimate any value between them — with the slope, the formula and the arithmetic all written out, plotted as you go.
Your numbers
Worked solution
y at x = 25
60
on the line through (10, 30) and (40, 90)
The line climbs 2 for every 1 step to the right, so at x = 25 the value is 60.
The working
3 stepsFind the slope between the known points
Linear interpolation assumes the value changes at a constant rate between the two points you know.
m = (90 − 30) ÷ (40 − 10) = 60 ÷ 30 = 2Walk along the line from the first point
y = y₁ + m·(x − x₁) = 30 + 2 × (25 − 10)Work out the result
y = 30 + 30 = 60- At x = 25
- 60
- Position between the points
- 50.0% of the way from x₁ to x₂
On the number plane
Use Left and Right Arrow, Home, or End to inspect data points.
Works instantly in your browser — nothing is uploaded, and the URL keeps your numbers so you can share the exact worked example.
Studying statistics or linear algebra? See every tool in the Stats & Algebra hub — variance, interpolation, RREF and eigenvectors, cross-linked.A proportion in disguise
Linear interpolation is just the proportion (y − y₁)/(x − x₁) = (y₂ − y₁)/(x₂ − x₁) solved for y — the same cross-multiplication you use for scaling recipes, applied to a line. If proportions click, interpolation is already familiar.
Frequently asked questions
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