Excel LET Function: Name Your Calculations for Cleaner Formulas

The Problem LET Solves

Consider this formula that checks a discount tier:

=IF(SUM(A1:A10)>1000, SUM(A1:A10)*0.1, IF(SUM(A1:A10)>500, SUM(A1:A10)*0.05, 0))

SUM(A1:A10) appears four times. Excel calculates it four times. The formula is hard to read.

How LET Works

Syntax: =LET(name1, value1, name2, value2, ..., calculation)

The same formula with LET:

=LET(total, SUM(A1:A10), IF(total>1000, total*0.1, IF(total>500, total*0.05, 0)))

total is calculated once and reused. Shorter, faster, clearer.

Multiple Names

LET can define multiple names:

=LET(sales, SUM(A:A), costs, SUM(B:B), profit, sales-costs, IF(profit>0, profit*0.3, 0))

Each name can use previously defined names. profit uses both sales and costs.

When to Use LET

• Repeated calculations: Any time you'd copy-paste a sub-formula
• Complex logic: Break down confusing formulas into named steps
• Performance: Expensive calculations (lookups, large ranges) should only run once

LET + Dynamic Arrays

LET shines with dynamic arrays. Calculate a filtered result once, then use it multiple ways:

=LET(filtered, FILTER(A:D, B:B="Active"), ROWS(filtered))

Filter once, count the results. Without LET, you'd have to filter twice.

Official Resources

• LET function — Microsoft's LET guide
• LAMBDA function — creating custom functions