AI in your spreadsheet: Claude for Excel, Copilot and ChatGPT for finance work

Until recently, using AI on a spreadsheet meant copying cells into a chat window and pasting the answer back. Now all three of the big assistants run inside Excel itself, in a side panel that can read the workbook, write formulas and change cells. For finance work that changes what's worth handing over.

This guide covers what each one is, the jobs they do well, where they go wrong, and the habit that keeps a model you'd sign.

The three assistants

As of September 2026, from each vendor's own page:

• Claude for Excel (Anthropic). An add-in from the Microsoft Marketplace, included on all paid Claude plans. It can explain any cell, change assumptions without breaking formulas, and build a model from scratch. It works in PowerPoint, Word and Outlook too, and it can use connectors to reach other data. Anthropic's page.
• Copilot in Excel (Microsoft). Built into Excel. Its Agent Mode can plan and make multi-step edits. It needs a Microsoft 365 Copilot license, or a Personal, Family or Premium subscription, and availability varies by region. Microsoft's guide.
• ChatGPT for Excel (OpenAI). An add-in for Excel and Google Sheets, with limited use on the free plans. It asks before it changes cells. OpenAI's help page.

Plans and features change every few months, so check the vendor's page before you choose. For most finance teams the deciding factors are dull: which one your firm has approved for client data, and which one you already pay for.

What they're good at

Reading a model you didn't build. Ask "walk me through how revenue is calculated on the Forecast sheet" and you get the chain of formulas in plain English, cell by cell. Of everything here, this is the job AI does most reliably, and it's where to start.

Finding the errors people make. Hardcoded numbers typed over formulas, SUM ranges that stop a row short, a growth rate that's different in one column. The formula audit skill does this as a structured review.

First drafts of structure. "Build a 13-week cash flow with receipts by customer and payments by vendor category" gets you a layout with formulas in a minute. It won't be your layout, but editing is faster than starting blank.

The formulas you look up every time. XLOOKUP with two criteria, a dynamic array that spills a filtered list, a date function for fiscal quarters that don't start in January.

Commentary from numbers. Variance commentary, a summary for the owner, notes on a board slide. See the variance commentary skill.

Where they go wrong

Arithmetic in prose. An assistant writing a sentence about the numbers can state a figure that isn't in the workbook. A number in a cell produced by a formula is safe; a number written into commentary is a claim to check.

Plausible structure, wrong logic. A generated model can look right and be wrong: interest calculated on the opening balance when it should be the average, or a tax line that ignores losses carried forward. Check every formula it wrote for a line that matters.

Intent it can't know. A formula that changes partway across a row may be a mistake or a deliberate change in policy. The assistant can flag it, but only you know which.

Data it shouldn't have. Everything in the workbook goes to the vendor. Client names, payroll, anything under an NDA: know your firm's policy and the plan's data terms before you open a client file with an assistant running.

The review habit

The assistants all make their edits visible. Use that:

1. Ask it to change nothing first. Start with questions and reviews. Let it write only once you've seen how it reads the model.
2. One change at a time. "Add a scenario toggle" is reviewable. "Improve this model" isn't.
3. Re-tie the outputs. After any change, check that the numbers that matter (net income, ending cash, the covenant ratio) moved only where you expected, and write down why.
4. Keep your name on it. The assistant drafts; the person who signs the model checks it. That's also the answer when a client asks whether AI built their forecast.

When the spreadsheet is the wrong place

A spreadsheet assistant works on the numbers in the workbook, which are an export: a snapshot of the books as of whenever someone pulled it. For questions about the books themselves (why margin fell, which transactions make up a balance, what next year looks like if you hire), an assistant connected to the ledger reads the source instead of a copy. The connected skills show what that looks like, and RoboLedger is how we set it up for our own books.