Linear Interpolation Calculator
Our linear interpolation calculator allows you to find a point lying on a line determined by two other points.
Interpolated y140interpolated within the known range
Fraction along40%
Slope10
Inside the known range?Yes
Equation of the liney = 10x + 0
The formula
y = y₁ + (x − x₁)(y₂ − y₁) ÷ (x₂ − x₁)
Interpolation versus extrapolation
Estimating between known points is interpolation and is usually safe. Estimating beyond them is extrapolation, and it assumes the straight-line trend continues — which is exactly the assumption most likely to be wrong. The calculator flags which one you are doing.