In a lot of small businesses, the real management software is called "Operations 2026 DO NOT DELETE.xlsx". The price list, the inventory, the technicians' schedule and the job tracker all live in a workbook that three or four people open every day. Before asking anyone to quote custom software, most owners ask a simpler question: now that Copilot is inside Excel, hasn't the file just become good enough again?
The pages that rank for "Copilot in Excel" explain how to turn it on and what to ask it. None of the ones at the top asks the expensive question: should this file still be a file? Copilot makes Excel more capable. It does nothing about the problems that come from keeping your data in a shared document.
The short answer, for the busy
Copilot in Excel genuinely helps with analysis: it writes formulas, builds PivotTables and charts, cleans up data and can edit the workbook itself. According to Microsoft's FAQ, it comes with Microsoft 365 business subscriptions that are eligible for Copilot Chat, with standard access, and with the paid Microsoft Copilot licence, with priority access. Other Microsoft pages, though, reserve editing for the paid licence. What it doesn't change is the nature of the file. When two people edit the same cell, the last save wins. The change history goes back 365 days, but a single edit made in a one-time-purchase version of Excel wipes it. Sheet protection, Microsoft writes, isn't intended as a security feature. When several people enter data every day, when you need to know who changed a price, when some people should only see part of the data, or when personal information travels as an email attachment, it's time to turn the spreadsheet into a small web app.
What Copilot in Excel actually does, as of October 2026
Microsoft's getting-started page describes three modes. In edit mode, the default, Copilot changes the workbook directly: it adds sheets, writes formulas across tabs, applies conditional formatting or data validation, and builds a PivotTable or a dashboard. In plan mode, it lays out its approach and waits for your go-ahead before touching the file. In chat mode, it analyzes the data without changing anything.
Three features matter for a small business. A Microsoft-provided skill, @clean-data, finds and fixes data issues. Custom skills, saved in a OneDrive folder, remember a procedure you repeat every month. A sheet named .Rules sets the conventions for a workbook, and it travels with the file when you share it.
On licensing, Microsoft labels the experience inside the app. "M365 Copilot (Basic)" means standard access without the paid licence, subject to service capacity; "M365 Copilot (Premium)" means the Microsoft Copilot licence (the product was called Microsoft 365 Copilot until recently) and priority access. Microsoft's own pages don't agree: Excel's product page and the service description for administrators reserve editing with Copilot for the paid licence (or, for consumers, Premium and Personal or Family plans with AI credits), while the FAQ, which is more recent, makes no such distinction. The simplest test: open Copilot in your own copy of Excel and see whether edit mode is offered.
One piece of advice repeated online is out of date: Microsoft now says Copilot works with AutoSave on or off. Another still holds, and Microsoft puts it in its FAQ: avoid relying on Copilot for decisions in sensitive areas such as finance or legal matters, and check everything it produces.
For writing the formula nobody remembers or summarizing six months of sales, it's a very good tool. The problem lies elsewhere.
Where the file breaks
Two people at once. Co-authoring works if the workbook lives in OneDrive or SharePoint Online and everyone uses a version of Excel that supports it. One person opening it in a version that doesn't is enough for everyone else to get a "file is locked" error. And when two people change the same thing, Microsoft is blunt: in general, the last change saved wins. Its advice for avoiding conflicts is to assign sheets or areas to each person by putting their names in heading cells. That's a convention, and nothing enforces it.
Who changed the price? Excel has an answer: Review, then Show Changes, which lists who edited which cell, when, and the previous value, going back 365 days. But Microsoft's help page lists what clears it: an edit made in a one-time-purchase or outdated version of Excel, or a file that was uploaded again, saved as a copy or replaced. Formatting changes aren't tracked, and a value changed by a VBA macro can show up without its previous value. One click on Reset Changes in Excel for the web empties the pane for everyone who uses the workbook. Version History still keeps earlier states of the file, without the cell-by-cell detail. Copilot can summarize the change history, but, Microsoft notes, it only reports what that history contains. The day a customer disputes a quote, "who changed this price, and when?" depends on a log a colleague can wipe without meaning to.
The macros of someone who leaves. A small business's most important file often holds VBA written by one person. Excel for the web can't create, run or edit VBA macros: you need the desktop app, and someone who understands the code. We described the same risk for Power Automate flows that belong to one employee. Copilot can help you read a formula, not replace the person who knew why column K exists.
Personal information as an attachment. A customer list with phone numbers and addresses, emailed to a sales rep who forwards it to an assistant, now exists in three copies you no longer control. Section 10 of Quebec's Act respecting the protection of personal information in the private sector requires security measures that are reasonable given the sensitivity of the information, its quantity, its distribution and the medium on which it is stored. A file passed around by email scores badly on the last two. A password on a sheet changes nothing: "Worksheet level protection isn't intended as a security feature," Microsoft writes. If your staff paste that data into an AI tool, the question belongs in your AI use policy.
What Copilot can't change: it's still a file
Copilot works inside the workbook, with the workbook's permissions. When you save its changes, Microsoft's FAQ reminds you, anyone with access to the file can see them. It adds no roles, no rules that apply to everyone, and no log that nobody can clear.
That's the trap. With Copilot, adding a tab, another formula or a dashboard takes two minutes. The operational file grows faster than before, carried by a tool that makes it cleverer without making it sturdier. The day you have to move off it, there will be more logic buried in cells to reconstruct.
A web app turns the arrangement around. The data lives in a database, separate from the screens. Each person signs in with their own account and sees what their role allows: a technician sees their own hours, not the salary column. The rules (a price never drops below cost, a closed job can't be edited) are checked by the server, whoever is typing. Every change leaves a line in an audit trail that no user can reset. And an Excel export stays one click away, for analysis.
The signs it's time for an app
Keep Excel if one person works in the file, or if it's an analysis or modelling tool. A spreadsheet is an excellent prototype. Move to an app when two or more of the following are true.
Several people enter data in the same file every day. You need to know who changed what, and the answer has to hold up in front of a customer or an accountant. Part of the data should be visible to some people and hidden from others. The file contains personal information and travels by email or on USB keys. Someone copies data by hand between the file and another system (an API integration can solve part of that). And only one person understands the macros.
One step remains before you have anything built: check that existing software doesn't already do the job. The tests in our piece on custom software versus SaaS apply as is. If a SaaS covers your process without bending it, rent it. If not, the custom tool doesn't need to be a downloadable "app": a web app opens in the browser, on a phone as well as at the office.
What about ChatGPT for Excel files?
To write a formula or decode an error, ChatGPT, Claude or Copilot Chat all do the job. The difference is the data: uploading the file to a chat tool creates one more copy, outside your SharePoint, under the retention rules of whatever subscription is being used. The comparison of subscriptions, and of where your data goes, is in our piece on Copilot, ChatGPT Business and Claude. Answering questions from all your files is a different project, covered in our piece on an AI assistant for company documents.
Where to start
Open your most important file and go to Review, then Show Changes. If the pane is empty although three people worked in it this week, or you can't tell who changed the last price line, you have your answer. Then list who edits the file, what each of them should see, and which columns hold personal information. That list is already half a specification.
At Peich, we build these internal tools: a database, screens for each role and an audit trail. And we'll tell you when Copilot and a well-kept file are enough.
→ Let's talk about your spreadsheet
This piece explains Microsoft features and licences that change often, and a legal obligation, to help a small business ask the right questions. It is not legal advice and does not replace Microsoft's documentation, which prevails: check what Copilot offers you in your own copy of Excel.
Written byXavier Peich