Analysing Excel with AI: Copilot, ChatGPT or an AI agent

What are the three routes, and how do they differ?

The three routes differ mainly in where the file is and whether the AI changes the original. Copilot works in the open workbook, ChatGPT and Claude calculate with an uploaded copy at the provider, and an AI agent such as Biwak reads the file in a folder on your computer and saves the result next to it.

Three routes compared (as of September 2026)
	Copilot in Excel	ChatGPT or Claude (upload)	AI agent in the folder, for example Biwak
Where the file is	In the open workbook	As a copy at the provider	In the working folder on your computer; content used goes to the language model
What changes	In edit mode, the workbook itself; in chat mode, nothing	Nothing in the original; result as an answer, chart or download	Result as a new CSV or HTML file; Biwak backs up the folder beforehand
Strengths	Formulas, PivotTables and charts directly in the workbook	Calculates with Python and shows the code	Several files at once, repeatable tasks, result as a file
Prerequisite	Suitable Microsoft 365 licence	Account with the provider; for Excel files in Claude, code execution switched on	Biwak account, internet connection, desktop app for macOS or Windows
Training on your data	Business accounts: according to Microsoft, no training of the foundation models; with Claude models, processing outside the EU Data Boundary	Personal accounts: depends on settings; business plans: not by default	No; processing happens in the EU, at Microsoft Azure in the EU Data Zone, or as a fallback via Prem AI (PREM SA, Switzerland)

What can Copilot in Excel do, and which licence do you need?

Copilot in Excel answers questions about your data, writes and explains formulas, creates PivotTables and charts and can edit the workbook directly. According to Microsoft's help pages, there are three modes (as of September 2026): in edit mode, Copilot changes the workbook; in plan mode, it first proposes a plan; in chat mode, the file stays unchanged. All three run in Excel on Windows, on the Mac and on the web. One of these licences is required:

a Microsoft 365 or Office 365 business subscription eligible for Copilot Chat, which gives standard access,
a commercial Microsoft Copilot subscription, i.e. the add-on licence with priority access,
for consumers, Microsoft 365 Premium or a Personal or Family subscription with an AI credits plan.

There are three points you should know beforehand. In edit mode, Copilot changes the file directly; according to Microsoft, anyone with access to the file sees the saved changes, including during co-authoring, and you can go back via Undo or earlier versions. So try Copilot on a copy first. In addition, Microsoft recommends in its FAQ on Copilot in Excel not to use Copilot for decisions in sensitive areas such as finance, law or medicine. And besides GPT models, Copilot in Excel also uses Anthropic's Claude models. In that case, according to Microsoft Learn (as of 3 September 2026), processing takes place outside the EU Data Boundary. For Microsoft 365 tenants in the EU, EFTA and the United Kingdom set up after 25 March 2026, the setting for this is switched on by default in Word, Excel and PowerPoint; for older tenants, Microsoft refers to the Message Center. Have your administrators check how it is set for you.

How do ChatGPT and Claude analyse an Excel file?

ChatGPT and Claude analyse an uploaded spreadsheet by writing and running Python code; the result appears as an answer, table, chart or downloadable file. According to OpenAI's help pages, ChatGPT accepts .xls, .xlsx and .csv files, spreadsheets may be around 50 MB depending on row width, and the free plan allows three uploads per day (as of September 2026). In Claude, code execution and file creation must be switched on for Excel files; Claude can then also create .xlsx files with formulas. For the Pro, Max, Team and Enterprise plans, there is also an Excel add-in called Claude for Excel.

The advantage: you see how the result was calculated. OpenAI itself recommends checking code, outputs and assumptions before relying on a result. The disadvantage: the file leaves your organisation. With personal ChatGPT accounts, OpenAI may use content for training as long as you do not switch off “Improve the model for everyone”; with Claude Free, Pro and Max, you decide yourself whether your data is used for training. ChatGPT Business, ChatGPT Enterprise, and Claude Team and Enterprise do not use inputs for training by default.

Twelve monthly exports, one overview: when does an agent in the folder fit?

An AI agent working in a folder fits when you analyse several files together, repeat a task every month or need the result as a separate file, such as an annual overview from twelve monthly exports. This is how Biwak works too: the spreadsheets sit in a working folder, the result is created next to them as a CSV file or HTML report, and the folder is backed up before every task. For Excel work, this means:

File formats: Biwak reads .xlsx, .xlsm, .ods and .csv, but not the old .xls format. Save such files as .xlsx in Excel first.
CSV instead of a finished Excel file: the desktop app reliably creates CSV, HTML and Markdown files; you open the CSV in Excel and continue working there. We do not promise finished .xlsx files for the desktop app; the tools for that exist only in the browser workspace, a preview feature.
Formulas in the workbook: if you want formulas, PivotTables or charts directly in your file, Copilot in Excel serves you better.
A checkpoint is not a backup: it only covers the working folder and keeps older states for a limited time only. So work with a copy of the original file.
Data path: the file stays on your computer; the rows used for the task go to the language model. So a customer list should only go in with customer numbers instead of names, as long as you have not assessed the processing.

Which analyses are suitable for AI?

Analyses whose result you can check with a simple test are well suited. The table shows typical tasks and the matching check.

Typical analyses and how to check them
Analysis	Example task	How to check
Totals by month and category	“Sum the amounts per month and cost centre for 2026.”	Grand total of the overview against `=SUMME()` (SUM) of the source column, one month with `=SUMMEWENNS()` (SUMIFS)
Plan vs. actual variances	“List all cost centres whose actual figure is more than 10% above plan.”	Recalculate two cost centres by hand; check whether rows without a plan value are missing
Duplicates	“Mark invoices that appear more than once with the same number and the same amount.”	Cross-check with the conditional formatting rule “Duplicate Values”; only mark, don't let anything be deleted
Classifying free text	“Assign each complaint to one of six categories and justify the assignment in a separate column.”	Classify 20 rows yourself and compare; have rows without a matching category listed separately

With free text, AI is genuinely ahead of a formula: categories, reasons or sentiment from comment columns. A PivotTable calculates plain totals just as well, without data leaving your organisation. In that case, have the AI build the formula or the PivotTable rather than just give you the figure.

How do you write an analysis as a task?

A good task names the file and sheet, the columns, the period, the desired result and the check to be supplied with it.

Task

Analyse the file “umsatz-2026.xlsx”, sheet “Bookings”. Only include rows dated from 1 January to 31 August 2026. Total the “Net” column per month and per cost centre and write the result to “auswertung-2026.csv”. At the end, state the number of rows read and excluded, with the reason, and the grand total. Do not change the original file.

Input: A bookings export as .xlsx with the columns Date, Cost centre, Account, Net and Booking text
Result: A CSV file with month, cost centre and total, plus a short report with row counts and the grand total.
Check: Grand total against =SUMME() (SUM) of the Net column for the same period, row count against =ANZAHL2() (COUNTA), recalculate two months with =SUMMEWENNS() (SUMIFS).

Have it calculated, not copied: ask for a formula, a PivotTable or the calculation path so you can see where a figure comes from.
Have exclusions named: empty rows, cancellations and subtotals should be counted and named, not silently dropped.
Specify German formats: decimal comma, dates as DD.MM.YYYY and, for CSV, a semicolon as separator, so that German Excel also opens the file correctly on a double-click.
Ask for German formula names: in German Excel it is SUMMEWENNS instead of SUMIFS, and a semicolon separates the arguments.

How do you check an AI analysis before passing it on?

Check every AI result against the source data before it goes into a report or a decision. Microsoft, OpenAI and Anthropic themselves point out in their help pages that results can be wrong.

Five checks for every analysis

Row count: does the number of rows processed match =ANZAHL2() (COUNTA) in the original, minus the exclusions named?
Grand total: do all subtotals together add up to the total of the source column, to the cent?
Samples: recalculate three values yourself, such as a large one, a small one and one from a month at the edge of the period.
Formulas: have every new formula explained and test it on a row whose result you know. Watch out for references that shift when copied.
Nothing deleted: according to Microsoft, “Remove Duplicates” deletes rows permanently. Have duplicates marked and decide for yourself.

If the data originally comes from a PDF, check the conversion first; what matters here is covered under Converting PDF to Excel.

What applies to customer data and other personal data?

If the spreadsheet contains names, customer numbers, salaries or other details that can be attributed to a person, the AI analysis processes personal data. You then need a data processing agreement with the provider, explained under DPAs for AI tools, and should check whether a data protection impact assessment is needed.

Only pass on the columns the analysis needs, and replace names with numbers where that is sufficient.
Use business accounts instead of personal accounts and check the training setting.
At Biwak, the DPA at biwak.ai/avv applies to businesses, with the technical and organisational measures in Annex III. Even so, personal data should only go in after your own assessment.
Record which data may go into which tool; what such a rule looks like is described in ChatGPT at work.

Frequently asked questions

Can ChatGPT analyse Excel files?

Yes. ChatGPT accepts .xls, .xlsx and .csv files and calculates with Python code that you can display; according to OpenAI, spreadsheets may be around 50 MB depending on row width. Check the code and the result, and remember that content from personal accounts may be used for training unless you switch this off.

Do I need an add-on licence for Copilot in Excel?

Not necessarily. According to Microsoft, a Microsoft 365 business subscription eligible for Copilot Chat gives standard access to Copilot in Excel, and the paid add-on licence brings priority access (as of September 2026). Consumers need Microsoft 365 Premium or a Personal or Family subscription with an AI credits plan.

Can AI write Excel formulas?

Yes. Copilot, ChatGPT and Claude suggest formulas and explain them; Copilot inserts them directly into the workbook. Test every formula on a row whose result you know, and pay attention to the German notation, with SUMMEWENNS instead of SUMIFS and a semicolon between the arguments.

Which Excel files can Biwak read?

Biwak reads .xlsx, .xlsm and .xltx, plus OpenDocument spreadsheets (.ods) and CSV files. Biwak does not read the old .xls format; save such files as .xlsx first. The desktop app reliably saves results as CSV, HTML or Markdown; we do not promise finished Excel files for the desktop app.

May I analyse customer data with AI?

That depends on the tool, on your contract with the provider and on the purpose. For personal data, you need a legal basis and a data processing agreement with the provider. Only pass on the columns that are needed, and replace names with numbers where this does not affect the analysis.

Sources

About this article

Responsible: Hermann Hampel, founder of Biwak. In his main occupation, Hermann Hampel leads a team for AI solutions at an industrial company, and he founded Biwak. Since 2017, he has been taking technology from idea to operation. Biwak itself offers an AI tool; wherever Biwak is mentioned, we therefore also state what it is not suitable for.

How this article was made:

Draft. Research and drafting are done with AI assistance, based on legislation and information from authorities and vendors that is linked in the article.
Independent check. A separate, AI-assisted review pass that did not write the draft checks the key legal, numerical and vendor details against the raw text of the sources, not against summaries, and checks the text against Google’s guidance on helpful content.
Review log. For every article, a log records which detail was checked against which source with which excerpt, and with what result. Blocked pages were read via the Official Journal of the EU or the web archive; no block was circumvented. The key details are checked, not every single sentence.

The information was last checked against its sources on 23 September 2026. No person has yet approved this article with name and date; the text was created with AI assistance. Errors or outdated information? kontakt@biwak.ai

How do you analyse Excel spreadsheets with AI?