Intro to Excel’s LET Function: Simplicity + Efficiency

Bottom Line: Simplify your Excel formulas and improve performance with the LET function. Learn how LET reduces repetitive calculations and makes complex formulas easier to read.

Skill Level: Intermediate

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Follow along with the same workbook used in this post.

It Pays to Learn the LET Function

The LET function is a game-changer for anyone looking to simplify complex formulas or improve performance in Excel. By allowing you to assign variables within your formulas, LET makes your work easier to read and significantly more efficient.

In this post, we’ll walk through an example of how LET can streamline your calculations, using a scenario from the logistics world.

What Is the LET Function?

At its core, the LET function allows you to:

1. Simplify formulas: Avoid duplicating repetitive logic, making formulas easier to understand.
2. Improve performance: Reduce the number of calculations Excel has to process.

Real-World Example: Calculating Shipping Weights

Imagine you’re managing logistics for a company that ships a wide variety of products. To streamline operations, the shipping department needs to know the weight of each product. This helps them decide whether to prepare the item for regular shipping or flag it for bulk freight.

You have a product list on one sheet that includes product IDs and their respective weights. On another sheet, there’s a list of orders that need shipping. The goal is to perform a lookup to retrieve the weight for each product and populate it in the orders list.

However, there’s an additional requirement:

• If the weight of a product is 40 pounds or more, it should be flagged as “BULK” instead of showing the actual weight. This informs the shipping department that the product requires special handling.

To achieve this, you’ll write a formula that dynamically retrieves the product weight and applies the bulk freight condition. Let’s see how we can handle this efficiently, first without using LET and then with LET.

Without LET

Here’s the formula:

=IF(XLOOKUP([@[Product ID]],tblProducts[Item],tblProducts[Weight])<40,XLOOKUP([@[Product ID]],tblProducts[Item],tblProducts[Weight]),"BULK")  

This approach duplicates the XLOOKUP logic, meaning Excel performs the same calculation multiple times, which is inefficient for large datasets.

With LET

Using LET, we can store the XLOOKUP result in a variable called "weight” and reuse it where needed:

=LET(weight,XLOOKUP([@[Product ID]],tblProducts[Item],tblProducts[Weight]),
IF(weight<40,weight,"BULK"))

Benefits of this approach:

• The XLOOKUP formula is only calculated once, improving performance.
• The formula is cleaner and easier to read.

How Does the LET Function Work?

Now that we’ve seen LET in action, let’s break it down. The LET function lets you define variables and assign them values within a formula. These variables can then be reused, making your calculations both cleaner and more efficient.

Arguments of the LET Function

The LET function uses these components:

1. Name1: The first variable name. We defined weight as the variable name.
2. NameValue1: The value or formula assigned to the variable. The result of XLOOKUP([@[Product ID]],tblProducts[Item],tblProducts[Weight]) is stored in the variable name weight.
3. Calculation: The final formula or calculation that uses the variable(s). Our example formula checks whether weight is less than 40. If true, it returns the value; otherwise, it returns “BULK”.

Here’s the formula again for reference:

By storing XLOOKUP in the variable weight, we avoid recalculating it multiple times, improving efficiency and clarity.

If you wanted to add multiple variables, you could do so by adding more Name and NameValue arguments before the final calculation.

How Much Faster Is It?

In a dataset with 1,000 rows, using LET reduced the number of calculations by 42%, significantly speeding up processing time.

I have a separate video that explains how to calculate this percentage change formula. You can access it here:

Key Takeaways

The LET function offers both clarity and efficiency, making it invaluable for modern Excel users. While it requires a bit of a learning curve, the payoff in performance and readability is well worth it.

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