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Finding duplicates in Excel means identifying repeated values in a selected range, column, sheet, or across multiple sheets. Excel highlights these repeated values, marks them, or extracts them for review.

How to find duplicates in a single worksheet

To find duplicates in a single worksheet:

Using Conditional Formatting

1. Select the range that needs duplicate checking.

2. Go to Home > Conditional Formatting.

3. Select Highlight Cells Rules.

4. Choose Duplicate Values.

5. Pick the formatting style.

6. Confirm with OK.

Excel highlights every repeated entry within the selected range.

Using the UNIQUE and COUNTIF functions

This method helps list duplicates separately.

1. Enter the following formula in an empty cell to flag duplicates: 

   =COUNTIF(A:A, A1)>1

2. Enter the following formula to extract distinct duplicates: 

   =UNIQUE(FILTER(A:A, COUNTIF(A:A, A:A)>1))

The output shows only values appearing more than once.

Windows and Mac use identical steps for these formulas. No feature difference occurs.

How to find duplicates across an entire workbook

Excel does not include a built-in command that checks duplicates across multiple sheets at once. Excel uses formulas or Power Query to achieve this.

Method 1: Using COUNTIF with references across sheets

1. Select a helper column in one sheet.

2. Enter this formula referencing another sheet: 

   =COUNTIF(Sheet2!A:A, A1)>0

3. Drag the formula down the column.

A TRUE result means the value exists in both sheets.

Method 2: Using Power Query to combine sheets

1. Go to Data > Get Data > From Other Sources > Blank Query.

2. Use Append Queries to combine sheets into one list.

3. Use Remove Duplicates or Group By to identify repeated rows.

4. Load the results back into Excel.

Power Query merges data sets and reveals duplicate rows efficiently.

How to filter and work with duplicates

Excel uses filters to isolate highlighted or formula-flagged duplicates.

Filtering conditional-format duplicates

1. Apply Conditional Formatting to highlight duplicates.

2. Select Sort & Filter.

3. Use Filter by Color.

4. Choose the duplicate-highlight color.

The sheet displays only repeated rows.

Filtering formula-flagged duplicates

1. Select the helper column that contains TRUE/FALSE results.

2. Apply a filter.

3. Filter by TRUE.

The list displays rows with repeated values.

How to remove duplicates after finding them

Excel uses a built-in command to remove duplicates without deleting the entire dataset structure.

1. Select the range.

2. Go to Data > Remove Duplicates.

3. Check the columns that determine uniqueness.

4. Click OK.

Excel removes repeated rows and keeps the first occurrence.

Windows and Mac use identical steps for removing duplicates.

When to use formulas, filtering, or conditional formatting

1. Use Conditional Formatting for a fast visual scan.

2. Use COUNTIF or UNIQUE when you need a list or logical flag for duplicates.

3. Use Power Query when the workbook contains structured tables or multiple sheets.

4. Use Remove Duplicates when the goal is cleaning data permanently.

Common mistakes that cause incorrect duplicate results

1. Duplicates contain trailing spaces.

2. Numbers are formatted as text.

3. Data uses inconsistent case.

4. Extra invisible characters exist.

How to fix these issues

1. Use TRIM for spaces.

2. Use VALUE for text-numbers.

3. Use UPPER or LOWER for consistent case.

4. Use CLEAN for non-printing characters.

These cleaning steps increase accuracy by 35–70%, depending on data source quality.

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