We can use the **Excel SUMPRODUCT function** to check **conditional formatting dates overlap in an array**. In easy steps, we will teach you how to use this function to handle array comparisons seamlessly.

*Figure 1: Result of using the Excel SUMPRODUCT function to check conditional formatting dates overlap*

**General Formula**

**=SUMPRODUCT((start_date<=end_dates)*(end_date>=start_dates))>1**

**Formula**

**=SUMPRODUCT(($C5<=$D$5:$D$9)*($D5>=$C$5:$C$9))>1**

**Setting up the Data**

- We will set up a list of
**Courses**in**Column B** **Column C**will contain the list of**Start Dates**for these courses- We will input the
**End date**for our list of Courses in**Column D** **Column E**will be titled**Overlap**. This is where we will insert the formula to check conditional formatting overlap and return the result as**TRUE**or**FALSE.**

* Figure 2: Setting up the Data*

**Applying the Excel SUMPRODUCT function**

- We will click on
**Cell E5** - We will insert the formula below into
**Cell E5**

**=SUMPRODUCT(($C5<=$D$5:$D$9)*($D5>=$C$5:$C$9))>1** **We will press the enter key**

* Figure 3: Using the Excel SUMPRODUCT function*

- We click again on
**Cell E5**and use the fill handle tool (a plus sign found at the base of**Cell E5**) to drag down the formula into the other cells.

*Figure 4: Result of applying the SUMPRODUCT function to check conditional formatting dates overlap in Excel*

**Explanation**

**=SUMPRODUCT(($C5<=$D$5:$D$9)*($D5>=$C$5:$C$9))>1**

The **Excel SUMPRODUCT function** can multiply ranges or arrays together to return with the sum of products. In our above illustration, we used the **Excel SUMPRODUCT function** to highlight cells where their dates overlap. It literally checks the start and end date of each course, against all start and end dates in our excel sheet respectively. However, this formula depends on two conditions to return with a **TRUE** result:

- The Start Date must be less than or equal (<=) to at least one other end date and the entire list or range.
- The End Date must be greater than or equal to (>=) to at least one other date in the data.

The formula works by:

- Checking a
**Course Start Date**against the other End Dates using the expressionThis will return with an outcome like this:`($C5<=$D$5:$D$9)`

.`{1,1,1,1,1}`

. - Next, it checks the
**Course start date**against other start dates using the expressionThis will return with an outcome like this:`($D5>=$C$5:$C$9)`

.`{1,1,0,0,0}`

.

It is solved like this:

**=SUMPRODUCT({0;1;1;1;1}*{1;1;1;0;0})>1**

**=SUMPRODUCT({0;1;1;0;0})>1**

**=TRUE**

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