In Excel: =LET(name, value, calculation) — LET names a value or a sub-expression once inside the formula and lets you reuse that name instead of repeating the calculation, e.g. =LET(total, SUM(B2:B20), IF(total>1000,"Over budget","OK")).
On this page7
Confirm you're on Excel 365 or Excel 2021+ — LET is not available in Excel 2019 or earlier.
Start typing =LET( and enter a name for your first value (any valid name, not a cell reference), a comma, then the value or expression itself.
Add more name/value pairs as needed, each separated by a comma.
End with the final calculation, which can use any of the names defined earlier in the same LET.
Reuse a name anywhere the underlying expression would otherwise have to be repeated, to speed up calculation and avoid copy-paste drift between repeated copies.
Need it as an auditable file?
Ships inside the linked template — formula-driven, unlocked, audit-ready.
What this does
LET solves a specific, common problem: a formula that repeats the same sub-expression several times, once for every place it is needed, which is slow to calculate and easy to get inconsistent when you edit one copy and forget the others. LET lets you compute that sub-expression once, give it a name, and reference the name anywhere else inside the same formula. It takes pairs of name/value arguments (up to 126 pairs) followed by a final calculation that can use every name defined before it. LET is an Excel 365/2021+ function — it is not available in Excel 2019 or earlier, and a workbook using it opens with #NAME? errors in an older version. Most people learn this as a sequence of clicks and forget it by next week; learning it as a pattern instead is what lets you apply it to the next, slightly different version of the problem without starting from scratch. That is the difference this page is trying to make. The difference between a quick fix and a sheet you can trust is the extra minute you spend validating “let formula excel”. Start on a copy or a tiny sample, keep the affected formula visible, and compare the result with the tool above before you touch the real workbook. When a formula is involved, keep the inputs labelled beside it, reference cells instead of typing values, and apply number formatting only after the result checks out. The point is a calculation you can defend to a CFO or an auditor, but the practical win is that someone else can open the file and understand what happened without asking you.
A worked example
Without LET, checking whether a total exceeds budget and showing the overage means computing SUM(B2:B20) twice: =IF(SUM(B2:B20)>1000,SUM(B2:B20)-1000,0). With LET: =LET(total,SUM(B2:B20),IF(total>1000,total-1000,0)) computes the sum once, names it total, and reuses that name in both the comparison and the subtraction. With B2:B20 summing to 1250, both versions return 250 — but the LET version only evaluates SUM once. LET turns a formula that repeats the same lookup or calculation three or four times into one that computes it once — faster to calculate, and safer to edit because there is only one copy of the logic to update. A practical tip before you scale it up: build it once on a small block of test data, confirm the number against the tool on this page, and only then point it at your real sheet. That one habit catches almost every mistake while it is still cheap to fix, long before a wrong figure reaches a report or a colleague.
In Google Sheets
Some functions on this page are newer additions to Excel: they are in current Microsoft 365 and Excel for the web, while older perpetual Excel versions return #NAME?. Google Sheets maintains its own function list, so confirm each function exists there before relying on the same formula. Keep this page bookmarked for the next time the same question comes up. Better still, repeat the steps once in your own workbook — doing it yourself is what turns a copied answer into something you remember. Here is the takeaway for “let formula excel”: copy the answer if you are busy, but if you have a spare few minutes, rebuild the example in Excel yourself with the tool above open beside it. That single pass — type it, run it, watch the result move when you change an input — is what turns a formula you found into a technique you trust. Keep your inputs labelled and referenced, never hard-coded, and the same sheet stays correct and auditable as it grows. Done that way, you will not need to look this up again, and you will be the person others ask.
Common mistakes
- Using a name that collides with an existing defined name or a cell reference like
A1, which Excel rejects or resolves ambiguously. - Forgetting LET requires Excel 365 or 2021+, then sharing a workbook with someone on an older version who sees
#NAME?instead of a result. - Nesting LET incorrectly by adding a name/value pair after the final calculation argument — every pair must come before the last, calculation-only argument.
- Using LET purely to make a formula shorter to read when the sub-expression is only used once — LET's benefit is reuse, not brevity, so a single-use expression gains nothing from it.
Frequently asked questions
What does the LET function do in Excel?
It names a value or expression once inside a formula so you can reuse that name instead of repeating the calculation, making the formula faster and easier to maintain.
What Excel version do I need for LET?
Excel 365 or Excel 2021 and later. It is not available in Excel 2019 or earlier.
Does Google Sheets have LET?
Yes — Google Sheets has had its own LET() function since 2022, with the same name/value/calculation pattern as Excel's. The syntax and behavior match closely enough that most LET formulas can be copied between the two apps unchanged.