# Decode a long Excel formula with Evaluate Formula and an LLM

> Paste the formula into ChatGPT or Claude for a plain-English explanation, then confirm each part with Evaluate Formula and F9 so you aren't relying on a wrong answer.

- **Category:** [Excel](https://stepgleam.com/categories/excel)
- **Difficulty:** Beginner
- **Time:** ~20 minutes
- **Tools:** ChatGPT, Excel (Microsoft 365)
- **Reliability score:** 78/100
- **Steps:** 5
- **Last updated:** 2026-10-26
- **Published:** 2026-10-26

## Tools used

- [ChatGPT](https://chatgpt.com) — Explains the formula in plain English
- [Excel (Microsoft 365)](https://support.microsoft.com/en-us/excel) — Evaluate Formula and F9 confirm the actual results

## What you'll get

A formula you understand piece by piece, with each piece's result confirmed in Excel.

## Who this is for

Anyone staring at a nested formula someone else wrote.

## Before you start

On r/excel, a top answer to "best way to audit a complicated formula" was to paste it into ChatGPT. The pushback was about trust: answers that are confidently wrong. The workable version uses AI for the explanation and Excel's own tools to prove it.

## Steps

### Step 1: Paste the formula into an LLM and ask for a breakdown

**Tool:** ChatGPT

Copy the formula from the formula bar and ask for an explanation of each part. Users in the thread: *"Throw it in ChatGPT and ask it to do it"*, and *"when it comes to excel formulas, VBA and small Python scripts - AI shines."* Say what the referenced cells contain.

**Prompt:**

```
Explain this Excel formula part by part, innermost first. B2 is an order date, C2 is a region code, and Rates!A:B is a lookup table. Formula: <paste>
```

[Open step 1](https://stepgleam.com/guides/decode-a-long-excel-formula-with-evaluate-formula-and-an-llm#step-1)

### Step 2: Treat the explanation as a hypothesis

Another user's caution: *"I think the real issue is the hallucinated responses which remove the trust."* Check it before you rely on it.

[Open step 2](https://stepgleam.com/guides/decode-a-long-excel-formula-with-evaluate-formula-and-an-llm#step-2)

### Step 3: Step through it with Evaluate Formula

**Tool:** Excel (Microsoft 365)

Select the cell, then **Formulas → Formula Auditing → Evaluate Formula**. Select **Evaluate** to compute the underlined part; use **Step In** to open a referenced formula and **Step Out** to go back. Compare each intermediate result with what the AI said.

**Why this works:** This shows what Excel actually computes, in order.

[Open step 3](https://stepgleam.com/guides/decode-a-long-excel-formula-with-evaluate-formula-and-an-llm#step-3)

### Step 4: Check any piece with F9

**Tool:** Excel (Microsoft 365)

In the formula bar, select one complete piece of the formula and press **F9** to see its value, then press **Esc** so you don't replace the formula with the value. It's one of the tools r/excel users list for understanding individual formulas.

[Open step 4](https://stepgleam.com/guides/decode-a-long-excel-formula-with-evaluate-formula-and-an-llm#step-4)

### Step 5: Test any AI rewrite on a copy

**Tool:** Excel (Microsoft 365)

If you ask the AI to simplify the formula, test the new one next to the old one on a copy. One user rates the advice at *"like 75% good"* and says *"you'd definitely want to save a copy and try it before moving on since it sometimes cranks out some non working formulas."*

[Open step 5](https://stepgleam.com/guides/decode-a-long-excel-formula-with-evaluate-formula-and-an-llm#step-5)

## Pro tips

- Ask the AI to rewrite the formula over several indented lines; it is easier to read.
- Ctrl+[ jumps to the cells the formula reads.

## Common mistakes

- Pressing Enter after F9, which saves the value instead of the formula.
- Accepting the explanation without stepping through it.

## FAQ

### Does Evaluate Formula work on everything?

Microsoft notes some limits, e.g. Step In isn't available the second time a reference appears.

### ChatGPT or Claude?

Users in the thread mention both. Either way, confirm in Excel.

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Canonical guide: https://stepgleam.com/guides/decode-a-long-excel-formula-with-evaluate-formula-and-an-llm
Read this guide as Markdown: https://stepgleam.com/guides/decode-a-long-excel-formula-with-evaluate-formula-and-an-llm.md