Calculation Issues

How to Calculate the Missing Percentage for a Target Average in Excel

Maira Mehtab Sep 27, 2026 870 views

Question details

The user needs to find the specific percentage required on a second day to achieve a desired overall average, given the known percentage of the first day.

Product: Excel
Device & OS: not provided
Scenario: Calculating a missing data point required to achieve a predetermined target average.
Observed behavior: The user needs a mathematical formula or an Excel tool to reverse-engineer an average calculation and find a missing component.

Before you start

Ensure that the cells you are working with are formatted as Percentages so the calculated decimal values display correctly, or remember to treat 22% as 0.22 in your formulas.

Solution 1Recommended

Use a Simple Algebraic Formula

Manually reverse the average calculation using basic algebra to find the missing percentage value.

The standard formula for an average of two numbers is (Value1 + Value2) / 2 = Target Average. To solve for the missing Value2, the equation can be algebraically rearranged to: Value2 = (2 * Target Average) - Value1.

Understand the numerical values

Convert your percentages to decimals for the formula. For example, a target average of 22% becomes 0.22, and the known Monday value of 26% becomes 0.26.

Enter the formula

Select a blank cell in your worksheet and type `=2*0.22-0.26`.

Calculate the result

Press Enter. The cell will output 0.18. Format this cell as a percentage to display it as 18%.

Dynamic References: Instead of typing the numbers directly, you can replace the numbers with cell references (e.g., `=2*B1-A1`) so the result updates automatically if your target or known value changes.

Solution 2

Use the Goal Seek What-If Analysis Tool

Utilize Excel's built-in Goal Seek feature to automatically find the missing value without manually rewriting the mathematical equation.

Calculate Averages Faster

Solve Target Averages Seamlessly with WPS Spreadsheet

You can easily calculate missing values and perform What-If Analyses using WPS Spreadsheet. It offers the exact same Goal Seek functionality and formula support as Microsoft Excel, making complex calculations effortless and accurate.

1. Open WPS Spreadsheet: Launch WPS Office, open a new spreadsheet, and enter your known percentage values.
2. Set up your AVERAGE formula: Create an `=AVERAGE()` formula that includes both your known cell and the empty target cell.
3. Access What-If Analysis: Go to the Data tab on the top ribbon and click on What-If Analysis > Goal Seek.
4. Find the missing percentage: Set your average formula cell to your target percentage, select the blank cell to change, and click OK to solve instantly.

Fully compatible with Microsoft Excel (.xlsx) formats and formulas.Built-in Goal Seek tool for advanced target average calculations.Lightweight software that calculates large datasets instantly.Free to use with a familiar, user-friendly tabbed interface.

microsoft office alternative - wps office

Frequently Asked Questions

How do I format my formula results as a percentage?

Select the cell containing your decimal result (like 0.18), go to the Home tab, and click the '%' icon in the Number formatting group. Alternatively, you can use the keyboard shortcut Ctrl+Shift+%.

Can Goal Seek find a missing value for an average involving more than two numbers?

Yes. If you have known values for three days and need the fourth day's value for a target average, set up the formula `=AVERAGE(A1:D1)`. Point Goal Seek to this formula cell, enter your target, and choose the empty fourth cell as the one to change.

Why is my algebraic formula returning a standard decimal instead of a percentage?

By default, Excel performs mathematical operations in standard number formats, calculating percentages as decimals. A result of 0.18 is mathematically equivalent to 18%; you just need to apply the Percentage number format to the cell to display the percentage symbol.

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