Extrapolation Calculator

Extend a trend beyond the observed data and quantify the growing uncertainty.

About Extrapolation Calculator

Extrapolation assumes the observed relationship continues unchanged. Uncertainty grows faster than linearly with distance beyond the data, which the widening multiple makes explicit. Extrapolating twice the observed range roughly triples the prediction interval, which is usually the point at which a forecast stops being useful.

Formula

Extrapolation

Extrapolation uses the fitted slope; uncertainty grows with distance beyond the observed range

uncertainty multiple: Factor by which the prediction interval widens outside the data

Worked example

With the default values below, Extrapolation Calculator returns Extrapolated Value of 290.00000. Change any input above and every figure here is recalculated in your browser.

Inputs used

First x value: 1
First y value: 100
Second x value: 10
Second y value: 190
Target x value beyond the data: 20
Residual standard errorminimum 0: 8

Results

Extrapolated Value: 290.00000
Distance Beyond the Observed Range: 10.0000
Uncertainty Multiple Against In-Range Prediction: 2.1688
Lower Bound: 255.9938
Upper Bound: 324.0062

Step by step

1Values used
2Extrapolation
3Extrapolated Value= 290.00000
4Distance Beyond the Observed Range= 10.0000
5Uncertainty Multiple Against In-Range Prediction= 2.1688
6Lower Bound= 255.9938
7Upper Bound= 324.0062

Assumptions and limits

The result is derived only from the 6 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 5 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

How is Extrapolation calculated?

Extrapolation uses the fitted slope; uncertainty grows with distance beyond the observed range Extrapolation assumes the observed relationship continues unchanged. Uncertainty grows faster than linearly with distance beyond the data, which the widening multiple makes explicit.

Why does Extrapolation matter?

Extrapolating twice the observed range roughly triples the prediction interval, which is usually the point at which a forecast stops being useful.

What values do I need to enter?

This calculator takes 6 inputs: First x value, First y value, Second x value, Second y value, Target x value beyond the data, Residual standard error. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.