# How to Compare Two Columns and Highlight Duplicate Values in Excel

Suppose we have two lists, list A contains some products serial numbers, list B also contains some products serial numbers, and some of them are found in list A as well. So, there are some duplicate values in list A and list B. If we want to find them out, we can though compare the two list to find out the duplicate values. Actually, in our work we often meet the situations that we need to compare two lists and find out the duplicate values. In this tutorial, we will help you to fix this issue by two ways, the first one, we can use Conditional Formatting function in excel; the second one, we can use formulas.

**Precondition:**

Prepare two columns. Column A and column B list product serial number. There are some duplicate values.

**Method 1: Compare Two Columns and Highlight Duplicate Values by Conditional Formatting Function**

**Step 1:** Select List A and List B.

**Step 2: **Click **Home** in ribbon, click **Conditional Formatting** in **Styles** group.

**Step 3:** In **Conditional Formatting** dropdown list, select **Highlight Cells Rules->Duplicate Values**.

**Step 4:** In **Duplicate Values** dialog, select **Duplicate** in dropdown list. Keep default value in **values with** dropdown list. Then click **OK**.

**Step 5:** Verify that all duplicate values in both column A and column B are marked with dark red properly.

**Method 2: Compare Two Columns and Highlight Duplicate Values by Formulas**

**Step 1: **Insert a new column between column A and column B. Then in B2, enter the formula **=ISNA(VLOOKUP(A2,$C$2:$C$12,1,FALSE))**. Click **Enter**, and we get **FALSE**.

In this formula, we can through **VLOOKUP** function to know whether value in column A exists in column B, if yes, **VLOOKUP **function will return matching value, otherwise it will return blank value, then we can use **ISNA** function (check whether a value is N/A) to get **TRUE** or **FALSE** value finally.

**Step 2:** Drag the fill handle down. Verify that B3:B12 are filled with **TRUE **or **FALSE** accordingly.

**Step 3:** Create a filter on column B. Click **Data** in ribbon, select **Filter** in **Sort & Filter** group.

**Step 4:** Click filter arrow in B1. Only check on **FALSE**, click **OK**.

**Step 5:** After above settings, duplicate values are filtered. Fill them with yellow.

**Step 6:** Clear column B, then in B2 enter the formula **=ISNA(VLOOKUP(C2,$A$2:$A$12,1,FALSE))**.

**Step 7:** Repeat above steps#2-#5 to highlight duplicate values in column C.

**Step 8:** Clear filter in column B. And delete column B. Verify that all duplicate values are highlighted.

**Comment:**

We can also use **COUNTIF** function here. Enter **=COUNTIF($C$2:$C$12,A2)** in B1, then we can get 1 for duplicate values or 0 for unique values.

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