Goal Seek runs a formula backward: you already know the answer you want, and it finds the input that produces it. On the Data tab, select What-If Analysis, then Goal Seek, and fill three boxes. Set cell points to the cell holding your formula, To value is the numeric result you want that formula to reach, and By changing cell is the one input cell Goal Seek may adjust. Select OK, and Excel changes that input until the formula lands on your target.
It sits alongside Scenario Manager and Data Tables under What-If Analysis, but this page stays on Goal Seek itself: the three boxes, the single-input rule, why the answer often is not a round number, and the fact that it writes its result straight over your input cell.
What does Goal Seek actually do?
Most of the time you feed a formula its inputs and read off the result. Goal Seek reverses that. As Microsoft frames it, Goal Seek takes a result and determines possible input values that produce that result. You supply the target and the formula, and Excel searches for the input value that gets the formula there.
That maps onto the three boxes in the dialog:
- Set cell holds the formula you want to resolve. This box must point at a cell that contains a formula, not a plain typed number, because Goal Seek needs something to compute.
- To value is the number you want that formula to equal. You type the target here, not into the worksheet.
- By changing cell is the single input the formula depends on. Goal Seek adjusts the value in this cell, and Microsoft notes that it has to be a cell the Set cell formula actually refers to. If the formula does not use that cell, changing it moves nothing.
How do I use Goal Seek? A worked example
Say you are pricing a product at 25 per unit and want to know how many units you have to sell to bring in revenue of 10000. Put the units in B1, the price in B2, and the formula =B1*B2 in B3. Then run Goal Seek with Set cell B3, To value 10000, and By changing cell B1.
| A | B | |
|---|---|---|
| 1 | Units sold | 400 |
| 2 | Price per unit | 25 |
| 3 | Revenue | 10000 |
To open the dialog, on the Data tab select What-If Analysis, then Goal Seek. On Windows the What-If Analysis button lives in the Forecast group; on a Mac it sits on the Data tab directly. Enter B3 in Set cell, type 10000 in To value, enter B1 in By changing cell, and select OK. Because B2 stays fixed at 25, the only lever Goal Seek has is B1, and it settles on 400.
Why is the answer often not a round number?
This example lands on a clean 400 because the model is a straight multiplication. Most models are not that tidy. Goal Seek reaches your target by controlled iteration, trying values and closing in, rather than by solving the equation on paper. Microsoft groups it with Solver on that point: “Both commands use iteration in a controlled way to obtain desired results.” So on a model with interest, growth, or anything nonlinear, the value Goal Seek writes into the changing cell is usually a long decimal rather than a neat figure.
Two things follow. First, Excel reports whether the run succeeded, and on some models it stops near the target without matching it exactly, so it is worth checking the result cell against the value you asked for. Second, the answer is only as good as the model: Goal Seek finds an input that makes the formula hit the number, which is not the same as finding the input you meant if the formula itself is off.
What Goal Seek will not do
Goal Seek handles exactly one variable. Microsoft is explicit that it solves for a single input at a time, so you get one By changing cell and one To value. If you need to solve for two inputs at once, or keep an input within a range, the Solver add-in is the tool for that: Microsoft describes Solver as a close relative of Goal Seek that can take on more variables.
The other catch is that Goal Seek is destructive to your input cell. It writes the result over the value in the By changing cell in place, and the workbook keeps no record of what was there before. If the original number matters, save a copy of the file first. Point By changing cell at a genuine input, one that holds a value rather than a formula, because whatever was in that cell is replaced by the number Goal Seek settles on.
The remaining two What-If tools are out of scope here. Scenario Manager stores named sets of input values so you can switch between them, and a Data Table shows how a formula responds across a row or column of inputs. Both answer a different question from Goal Seek’s single backward solve, and each is its own topic.
The short version
- What it is: Goal Seek finds the input value that makes a formula reach a result you choose. Open it from Data > What-If Analysis > Goal Seek.
- The three boxes: Set cell is the cell holding the formula, To value is the numeric target you want that formula to reach, and By changing cell is the one input cell Goal Seek may adjust.
- The formula must use the input: the cell in By changing cell has to be referenced by the formula in Set cell, or changing it does nothing.
- One variable only: a single changing cell and a single target. For several inputs or constraints, use the Solver add-in.
- It overwrites in place: the result is written over the value in By changing cell with no copy of the original, so save the file first if that number matters.
- Approximate by design: Goal Seek reaches the target by iteration, so the answer is often a non-round number, and it reports whether it found a solution.
- Not the same as: Scenario Manager (named sets of inputs) or a Data Table (a grid of results), the other What-If Analysis tools.
