Calculators
Linear Interpolation Calculator
Estimate y from two known points and a target x, with interpolation and extrapolation identified privately in your browser.
Estimate a value between two known data points.
Linear interpolation assumes a straight line between (x₁, y₁) and (x₂, y₂). Calculate t = (x − x₁) / (x₂ − x₁), then y = (1 − t)y₁ + ty₂. For points (0, 0) and (10, 100), x = 5 gives t = 0.5 and y = 50. Known points may be entered in either order, but their x coordinates must differ. Targets outside the known x range are labeled extrapolation; extending a line beyond measured data may be unreliable. This method assumes a linear relationship and does not fit curves or estimate uncertainty. Enter finite numbers without thousands separators; signed decimals and scientific notation are supported. Results use browser floating-point arithmetic and display up to 12 significant digits. All processing stays in your browser.
Frequently Asked Questions
Everything you need to know about this tool, how it works, and privacy.
How do you calculate linear interpolation?
Calculate t = (x − x₁) / (x₂ − x₁), then y = (1 − t)y₁ + ty₂. Between (0, 0) and (10, 100), a target x of 5 gives y = 50.
Can I extrapolate outside the two points?
Yes. A target outside the known x range extends the same straight line and is labeled extrapolation. Its accuracy depends on whether the underlying relationship remains linear.
Can the points be reversed or have equal x values?
Reversing the points gives the same mathematical result. Equal x coordinates are rejected because they do not define a unique y for a target x.
How precise are the results?
The calculator uses browser floating-point arithmetic and displays up to 12 significant digits. Extreme magnitudes can exceed the numeric range and produce a validation message. Data stays in your browser.