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Interpolation Calculator

Estimate a value between known data points using linear or polynomial interpolation.

Interpolate a value

Interpolated y: —
Method: — · Points: —
Linear mode joins the nearest two points; polynomial mode fits a Lagrange curve through every point.

How to use the Interpolation Calculator

  1. Type your data points, one x,y pair per line.
  2. Enter the x value you want to estimate and choose the method.
  3. Read the interpolated y value and the points that were used.

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Frequently Asked Questions

Common questions about the free online interpolation calculator.

Interpolation estimates a value that lies between known data points, which is useful for filling gaps in tables and measurements.
Type the pairs as numbers, such as 0, 0; 10, 100. Separate the numbers with commas or spaces and the pairs with semicolons.
Linear mode joins the two nearest points with a straight line, while polynomial mode fits a Lagrange curve through every point.
The tool extrapolates using the closest segment and reminds you that the answer lies beyond the data you supplied.
Answers are exact for linear data and mathematically exact for polynomial fits, with the display rounded to four decimals.
No. Two points sharing the same x value make polynomial interpolation undefined, so the tool asks you to fix them first.
No. The data points you type stay in your browser and every calculation runs locally on your own device.
Use linear for a quick estimate between two nearby readings, and polynomial when your points follow a smooth curve.

Last updated: October 10, 2026