Use Goal Seek in Gnumeric to Find an Input Value

Goal Seek is useful when you know a desired formula output but not the input required to produce it. The Gnumeric manual places this feature under Tools → Goal Seek. It searches by changing one input value; it does not solve a multi-variable planning problem.

Build a tiny example

Enter these three cells in a blank Gnumeric worksheet:

Cell	Entry
B1	5
B2	=3*B1+2
B3	47 (target recorded for reference)

At first, B2 displays 17 because 3×5+2=17. The desired output is 47. Algebra gives B1 = (47 − 2)/3 = 15.

Configure Goal Seek

1. Open Tools → Goal Seek (the location in the official Gnumeric manual).
2. Identify the formula cell B2 as the output to match and set the desired result to 47.
3. Identify B1 as the numeric value the tool is permitted to change.
4. Run the search, then verify that it proposes a value near 15.
5. Inspect the formula again after accepting the suggestion: 3×15+2=47.

When the solver’s suggestion is misleading

A formula can have several solutions, no solution, or a discontinuity. The starting guess can affect whether an iterative search converges. For a single simple linear formula such as this example, the answer is unique; for X²=16, both +4 and −4 would solve the mathematical target.

If the formula cell does not depend on the allowed input, the solver has nothing useful to vary.

Further learning

For two inputs and capacity constraints, see Gnumeric Solver optimization. For a similar task in another program, see PlanMaker Goal Seek.

Verification: The exact algebraic solution was independently checked. Tool configuration is documentation-based; no Gnumeric application was run.

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Official documentation: Software manual or vendor release notes. The workflow follows the linked documentation; confirm the interface and outputs in your installed version because no native-application test is documented for this guide.