Use AI to Explain and Fix Excel Formulas and Errors

Every office has a spreadsheet nobody understands: a file built years ago, full of long formulas, that everyone is afraid to touch. AI is excellent at explaining these formulas in plain language, and at finding out why one has stopped working.

Explain a formula

Click the cell, copy the formula from the formula bar, and ask:

Explain this Excel formula to someone who knows basic Excel. Go step by
step from the inside out, then say in one sentence what it returns.

=IFERROR(INDEX(Rates!$C:$C, MATCH(1, (Rates!$A:$A=B2)*(Rates!$B:$B=C2), 0)), "Check rate")

The AI will explain that it looks up a rate in the Rates sheet where both column A matches B2 and column B matches C2, and shows "Check rate" if no match is found.

Add context for a better explanation: "Sheet Rates has Supplier in A, Product in B and Rate in C."

Explain a whole sheet

For a complicated sheet, paste several formulas together with their cell addresses:

These are the formulas in my costing sheet. For each one, explain what
it does in one line, then tell me how the cells depend on each other.

D5: =B5*C5
E5: =D5*VLOOKUP(A5,GST!A:B,2,FALSE)
F5: =D5+E5
F20: =SUM(F5:F19)

Fix an error

Excel errors each mean something different:

Error	Usually means
`#N/A`	A lookup did not find the value
`#VALUE!`	Wrong type of data, often text where a number or date is expected
`#REF!`	The formula points to cells that were deleted
`#DIV/0!`	Dividing by zero or an empty cell
`#NAME?`	A misspelt function, or a function your Excel version does not have
`#SPILL!`	A formula that returns several results is blocked by cells that are not empty

Give the AI the formula, the error, and what the cells contain:

This formula in E5 shows #N/A:
=VLOOKUP(A5, GST!A:B, 2, FALSE)
A5 contains "Desk Lamp ". The GST sheet has "Desk Lamp" in column A.
Why is it failing and how do I fix it?

The AI will spot the extra space after "Desk Lamp" in A5 and suggest TRIM(A5), or cleaning the data (covered in the next lesson).

Find the cause yourself, with AI as a guide

Excel has built-in tools that the AI can walk you through:

Formulas → Evaluate Formula steps through a formula one part at a time.
Formulas → Trace Precedents draws arrows to the cells a formula uses.
Selecting part of a formula in the formula bar and pressing F9 shows its value. Press Esc afterwards, or the formula will be replaced by the value.

Walk me through using Evaluate Formula to find where this formula goes
wrong: [paste formula]

Fix safely

Before changing an inherited sheet:

Save a copy of the file first.
Change one cell, check the result, then copy the fix to other cells.
Compare totals before and after. If a total changes, find out why before you continue.
Write a short note in the sheet (a comment or a "Notes" tab) about what you changed.

Practice task

Find the longest or most confusing formula in a spreadsheet you use. Ask the AI to explain it step by step. Then break it on purpose in a copy of the file (for example, add a space to a lookup value) and ask the AI to diagnose the error from the formula and the cell contents.

Key takeaways

Paste a formula and ask for a step-by-step, inside-out explanation.
Each error type points to a typical cause; give the AI the formula, error and cell contents.
Use Evaluate Formula, Trace Precedents and F9 (then Esc) to find problems.
Always work on a copy, change one cell first and compare totals.