Answer

To find duplicates in multiple columns in Excel, use conditional formatting, helper formulas, or advanced filtering, depending on whether the duplicate must match across all selected columns or within any individual column.

Method 1: Find Duplicates Across Multiple Columns Using Conditional Formatting

This method identifies rows where the combined values across multiple columns appear more than once.

Steps

1. Select the full data range that contains all relevant columns.

2. Go to Home → Conditional Formatting → New Rule.

3. Select Use a formula to determine which cells to format.

4. Enter the formula below, adjusting column letters and row numbers to match the dataset:

   =COUNTIFS($A:$A,$A1,$B:$B,$B1,$C:$C,$C1)>1

5. Click Format, choose a highlight style, then select OK.

Explanation

• COUNTIFS evaluates duplicates using all specified columns as a single combined key.

• A result greater than 1 confirms duplication.

• Entire rows that share identical values across the selected columns are highlighted.

Windows vs Mac

• No functional difference.

• Menu names and formula behavior remain identical.

Method 2: Find Duplicates in Any of Multiple Columns

This method highlights duplicate values that repeat within any column independently.

Steps

1. Select all relevant columns.

2. Go to Home → Conditional Formatting → Highlight Cells Rules → Duplicate Values.

3. Choose Duplicate.

4. Select a format style.

5. Click OK.

Explanation

• Excel evaluates each column separately.

• A value repeating in one column triggers highlighting.

• Cross-column comparison does not occur.

Method 3: Use a Helper Column for Exact Row Duplication

This method flags duplicate rows using a visible indicator.

Steps

1. Insert a new column to the right of the dataset.

2. Enter the formula below in the first row of the helper column: 

   =COUNTIFS(A:A,A1,B:B,B1,C:C,C1)

3. Fill the formula down.

4. Filter the helper column for values greater than 1.

Explanation

• The helper column displays frequency counts.

• Values greater than 1 confirm duplication across all specified columns.

• Filtering isolates duplicate rows instantly.

Method 4: Use Advanced Filter to Extract Duplicates

This method extracts duplicates into a separate area.

Steps

1. Select the full dataset including headers.

2. Go to Data → Advanced.

3. Select Copy to another location.

4. Check Unique records only to isolate non-duplicates.

5. Compare extracted results against the original dataset.

Explanation

• Advanced Filter processes entire rows.

• Comparison across columns occurs row by row.

• This method suits audit and review tasks.

Windows vs Mac

• Windows: Data → Advanced appears directly.

• Mac: Data → Advanced Filter appears under the Sort & Filter group.

Method 5: Use Power Query for Large Datasets

This method handles large datasets with higher accuracy and repeatability.

Steps

1. Select the dataset.

2. Go to Data → From Table/Range.

3. Load the data into Power Query.

4. Select the relevant columns.

5. Choose Remove Rows → Remove Duplicates or Keep Duplicates.

6. Load results back into Excel.

Explanation

• Power Query compares rows across selected columns.

• Processing occurs outside the worksheet.

• Refresh capability maintains accuracy as data changes.

Windows vs Mac

• Windows supports full Power Query features.

• Mac supports Power Query with limited interface controls.

Key Accuracy Rules for Duplicate Detection

1. Blank cells count as valid values during duplicate evaluation.

2. Leading and trailing spaces create false uniqueness.

3. Text case does not affect duplicate detection.

4. Numeric formatting does not affect duplicate evaluation.

5. Formula results are evaluated, not the formulas themselves.

Best Method Selection

• Conditional Formatting suits visual review.

• Helper columns suit validation and reporting.

• Advanced Filter suits extraction.

• Power Query suits large or recurring datasets.

Each method produces deterministic results when column ranges remain consistent.

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