Everyday Tools

Linear Interpolation Calculator

Estimate an intermediate y value from two known points and a target x value.

Updated April 14, 2026
Free online tool
Planning and research use

Why this page exists

Intermediate values are easier to estimate when two points are turned into a straight-line result instead of being worked out by hand each time. This calculator helps visitors estimate a y value at a target x using linear interpolation.

Interactive tool

Run the estimate

Enter your numbers and read the result first, then use the sections below to understand what affects the outcome.

Calculator

Linear interpolation calculator

Estimate an intermediate y-value between two known points at a target x-value using linear interpolation.

Result

30.000000

Estimated interpolated y-value at the target x-position based on the two points entered.

Interpolated y value30.000000

Input points used(10.0000, 24.0000) and (18.0000, 40.0000)

Target x used13.0000

Slope across points2.000000

Moving from (10.0000, 24.0000) to (18.0000, 40.0000) and evaluating x = 13.0000 gives an interpolated y near 30.000000.
This treats the interval between the two points as a straight line, so it is most useful when a linear assumption is reasonable.
Use the result for quick math, engineering, or table-look-up checks when you need an intermediate value between two known points.

This is a standard straight-line interpolation estimate. It assumes the change between the two known points is linear over the interval used.

Planning note

Last updated April 14, 2026. Use this tool to compare scenarios and plan ahead, then confirm important details with the lender, employer, insurer, contractor, or other qualified provider involved in the final decision.

How it works

What the calculator is doing

Enter the two known points and the target x value.

The calculator applies the standard linear-interpolation formula across the two points.

It shows the interpolated y value, the points used, and the target x value.

Understanding your result

This is a straight-line estimate. It works best when a linear change between the two known points is a reasonable assumption for the interval used.

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Examples

Ways people use this tool

Example scenarios help turn a quick estimate into a more useful comparison or planning step.

Estimate a value between table entries

Linear interpolation can make chart and table lookups faster when the exact x value is not listed.

Check engineering or lab values quickly

Two known points can often be enough to estimate a nearby value without a full spreadsheet model.

Use it with coordinate tools

Interpolation often fits naturally beside slope, midpoint, and distance tools when you are working through graph-based problems.

FAQ

Common questions

How is linear interpolation calculated here?

The calculator uses the two known points to define a straight line and then estimates the y value that matches the target x position on that line.

What happens if the target x is outside the two points?

The math still works, but the result is really a straight-line extrapolation rather than an in-between interpolation estimate.

Why do the two x values need to be different?

If both known points share the same x value, a unique straight-line interpolation slope cannot be calculated from that pair.

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Keep comparing

Use these related tools to compare nearby scenarios, check a second estimate, or keep narrowing down the right decision.

Everyday ToolsUpdated April 12, 2026