How I Use Microsoft Copilot Cowork For Finance

Microsoft shipped Copilot Cowork to general availability on June 16, 2026, and most finance teams still have not clicked the toggle. If your company pays for Microsoft 365 Copilot, there is a good chance the license already covers it and nobody sent an email.

I spent a weekend on it and came out with something I did not expect. My monthly variance commentary now writes itself on the third business day of the month and emails me the finished document. I do not open anything.

This is the whole path in the order I would walk it if you are starting from zero. Setup and one small job first, then three builds that each add exactly one thing, ending with the part where you stop typing the prompt at all. You will also see the two places it got things wrong, because both are worth knowing before you trust it with a real close.

What Is Copilot Cowork?

Copilot Chat answers a question. You ask, it drafts, you copy the answer somewhere useful. One turn, one output, and you do the assembly.

Cowork takes the whole job. You describe the outcome, it breaks the request into steps, opens the files, runs its own analysis in the background, writes the workbook and the memo and the deck, and asks your permission before anything leaves the building.

	Copilot Chat	Copilot Cowork
Shape of the work	One question, one answer	Multi-step job, multiple deliverables
Time to finish	Seconds	Minutes
What you get back	Text you paste somewhere	Actual files in your OneDrive
Takes actions?	No	Yes, with approval gates
Best for	A quick draft or explanation	Close work, reviews, recurring reporting

Two things worth knowing before you start. Cowork runs on Anthropic’s Claude models for most of the reasoning work, which surprises people who assume Microsoft’s agent is running Microsoft’s model. And it is billed on usage rather than a flat seat fee, so your admin can see consumption per user and set limits.

The mental model that helps: treat Cowork like a coworker you brief once and check on later.

Where the files live matters more than anything else

Claude Cowork and ChatGPT’s work mode were both designed around files on your own computer, and their cloud versions arrived later. Microsoft went the other direction. Cowork was built for OneDrive and SharePoint from day one, which is why the desktop app and the browser version have the same capability.

The practical consequence: Cowork cannot see anything on your hard drive. Not your desktop, not a mapped network share. If the file is not in OneDrive or SharePoint, it does not exist as far as the agent is concerned.

What you need before you start

• A Microsoft 365 Copilot license. Cowork is a mode inside it, not a separate purchase. If the Cowork toggle is missing next to Chat, that is an admin setting rather than a licensing problem.
• A OneDrive or SharePoint folder with your files in it. I keep one folder for this and point at nothing else.
• Files under 200 MB each. This one bites, and I will cover the workaround below.
• Unencrypted files. Cowork cannot read encrypted files even when you personally have access.
• A rough idea of what “done” looks like. The single biggest quality lever is describing the deliverable rather than the analysis.

Build 1: give it three deliverables in one prompt

I started with something a controller does every month and nobody enjoys: reviewing bank data.

Six months of daily activity across three locations, four accounts each. About 2,900 transactions and roughly 2,000 daily balance rows. Nobody had reviewed the file.

The important part of the prompt is that I asked for three separate things at once, and one of them touches the outside world.

Prompt: I've attached our bank data for three locations, January through
June 2026. Two sheets: daily closing balances and individual transactions.

Do a full cash review and give me back three things:

1. An Excel workbook named "Cash Exceptions Q1-Q2 2026" with one tab
   listing every day any account closed below zero, and a second tab
   listing every transaction you believe is a duplicate, an error, or out
   of pattern. Add a column with your reason for each one.

2. A one page Word memo I can hand my CFO explaining what caused the
   largest cash problem in the period, traced to the specific transactions
   that caused it, with the dollar impact.

3. A draft email to the Astoria location manager asking about the items
   you flagged for her location. Leave it in my drafts, do not send it.

Work through the transactions yourself. Totaling the categories is not enough.

What came back

The workbook led with an overview: nine negative balance days and a peak overdraft. The negative balance tab explained what happened on each of those days. The flagged transactions tab listed every item it thought was wrong, with columns for the transaction ID, location, account, counterparty, memo, and a plain-English reason. Errors, out of pattern, duplicates. It even added a note that a couple of the duplicates looked recoverable.

Then it traced the cause. One operating account went underwater and bottomed near negative $38,000. The reason was a $320,000 debit for espresso machines and a store buildout, approved without anyone checking the cash position first. There is an overdraft penalty later in the period, which is the hangover from that decision.

And on the flagged tab: $62,000 of payroll, run twice. A vendor invoice paid twice on the same day. A bank fee charged twice.

I never used the word overdraft in the prompt. I asked for a cash review.

The approval gate, and where the email ended up

The memo appeared in the output folder. The email did not, and that confused me for a second until I checked Outlook. It was sitting in my drafts, addressed and written, signed off with a note that it was sent by Copilot Cowork.

That is the part people underestimate. Cowork is wired into the whole Microsoft suite, so an email it drafts lands in your actual mailbox rather than in a text box you have to copy out of. Anything that sends, posts, or schedules stops and asks first, and you can either approve it once or tell it to stop asking for the rest of the session.

Read the approval card before you approve it. There is a “show parameters” option that gives you the technical detail of what it is about to do.

Build 2: the file Excel refuses to open

Excel tops out at 1,048,576 rows per worksheet. The part that costs people money is what happens next: Excel does not refuse the file, it loads the first million rows and tells you it truncated in a dialog most of us click straight through.

So the analysis runs. The numbers look reasonable. Nobody finds out the report was built on a fraction of the data.

My point of sale file has 4.5 million rows covering 18 months, three locations, and nine product categories. It is 497 MB on disk.

The 200 MB workaround nobody documents

Cowork’s attachment limit is 200 MB and my file is 497. Zip is a supported file type, and a CSV of transaction data compresses roughly seven to one, so the zipped file comes in around 68 MB. Cowork unpacks it on the other side and reads the whole thing.

I could not find that in any documentation. It is just what works.

Asking it to clean the data before it calculates anything

The store location column in this file is deliberately messy, the way real exports are messy. Some values in all caps, some in lowercase, some with a trailing space. A tool that trusts what it is handed reports six locations instead of three, and every number underneath is wrong.

So I made cleaning the first instruction rather than an afterthought.

Prompt: This zip contains about 4.5 million point of sale transactions
across three locations, January 2025 through June 2026. Unzip it and read
the whole file, not a sample.

Before you analyze anything, clean the store_location column. The values
are inconsistent. Some are uppercase, some lowercase, some have trailing
spaces. Normalize them to three locations and tell me exactly how many
rows you corrected and what the bad values were.

Then build an Excel workbook with revenue and units by location by month,
revenue by product category ranked, and transaction volume by hour for
each location, weekday versus weekend.

Then build a 6 slide PowerPoint for our quarterly ops review using those
charts. Tell me the total row count you processed so I know you read all of it.

It reported the bad values it corrected, then produced a workbook with data tables and charts on every tab. Twelve steps ran in total, and I could watch each one appear in the workspace panel as it went.

The deck was the part I did not expect to be useful. It pulled three operational recommendations out of the hourly and product mix data: coffee and tea drive 62% of revenue, weekday and weekend customers arrive at the same hours so there is no case for separate schedules, and the long tail of packaged goods is not earning its shelf space.

Those are real merchandising observations from 4.5 million rows, produced in one pass.

Build 3: stop typing the prompt

Two builds in, I had typed two long careful prompts. That is fine once. As a monthly process it falls apart, because the prompt drifts, and when the prompt drifts the output drifts with it. You find out when somebody asks why this month’s memo reads differently.

The fix is a skill file.

What a skill file is

A skill is a markdown file (a plain text file with light formatting marks) that tells Cowork how you want a specific job done. It has a name, a description, and a set of instructions, roughly what you would hand a new analyst on their first month-end. You can write one in Notepad. You get 50 of them, and each can carry up to 20 supporting files.

If you have built skills for Claude, the format is identical and the files move straight across.

Let Copilot write it for you

Here is what I did rather than writing the markdown by hand. I already had a standard operating procedure for month-end commentary written out in plain English. So I pasted the whole thing into Cowork and asked it to turn that into a skill file and save it.

It loaded a skill-management skill and a skill-design skill on its own, wrote the file, and then stopped and asked my approval before installing it. The skill appeared under outputs and under skill management, ready for every future session.

Opening that markdown file on your desktop in Notepad looks like a mess if you have never seen markdown. Open it inside Cowork and it renders cleanly, with the calculation steps, the guardrails, and the output rules all readable.

If you have a process documented anywhere, in a Word doc, a wiki page, an email to your team, you are one paste away from a skill file. That is the shortest path from “we do it this way” to “it does it that way.”

Putting it on a schedule

The last step took one sentence.

Prompt: On the third business day of every month, run my Monthly Variance
Commentary skill for the month that just closed, using the P&L and manager
comments files in my OneDrive month end folder, and email me the Word
document when it's finished.

Cowork built the recurring task and asked for approval, the same way it did for the skill. You get options: run it once now to watch it work, schedule it, or always allow so it stops asking. I scheduled it.

The Scheduled page then showed the job with its next run date and full instructions. There is a Runs tab that builds an audit log of every execution and what it did, which is the thing that will matter the first time somebody asks you to explain an output.

You get five scheduled prompts. That sounds limiting until you treat them as headcount rather than as tasks, and then five is a real budget you have to think about.

Where it still needs a human

Two things went sideways in the same session.

The CFO memo was too long. The information in it was correct and traced back to the workbook properly, but it was verbose in a way no CFO reads. Good content, wrong format. A follow-up asking it to cut the memo to five bullets would fix it in thirty seconds, and I would build that instruction into the skill file rather than asking every month.

It put data quality on slide 5 of the ops deck. I asked it to, so this one is on me, but seeing it in the flow made the mistake obvious. Data quality notes belong in an appendix or an email to whoever owns the source system. They do not belong in a deck you are presenting to store operators.

The pattern in both: Cowork gets the analysis right and the judgment about audience roughly right. The last 10%, the “would I put my name on this” pass, is still yours.

Common issues you will hit

The Cowork toggle is not there. That is an admin setting rather than a license problem. Your Microsoft 365 admin controls availability in the admin center, and they can also turn individual models on and off. Ask before you assume you need to buy something.

Your file is over 200 MB. Zip it. Zip is a supported type and it unpacks on the other side. If a single file is still over the limit zipped, split it by period and attach the pieces.

Cowork cannot see the file you are pointing at. It only reads OneDrive and SharePoint. A file on your desktop or a network drive is invisible to it. Move it, then attach it through the cloud file picker rather than uploading from your device.

It cannot read an encrypted file. Even when your own account has access. There is no workaround for this one short of an unencrypted copy in an appropriate location.

It will not delete anything. Cowork can create and update files in OneDrive and SharePoint, and it cannot delete files or folders. That is by design and it is the right call.

What this costs

Cowork bills on usage rather than a flat seat fee. Model responses, tool and skill calls, image generation, and browser tasks all count toward consumption, and your admin sees it in the Microsoft 365 admin center and can set limits per user or group.

Practically, the 4.5 million row job was the expensive one in my session. A single variance workbook off a P&L is cheap. Something to keep in mind when you build the business case: price it at the volume and turn count you will run in production, well above the three or four turns you ran by hand while testing.

Where I would start this week

Do not start with the 4.5 million row file. Start with the smallest job you can describe completely.

1. Put last month’s actuals and budget in a OneDrive folder.
2. Open Microsoft 365 Copilot and switch the toggle from Chat to Cowork.
3. Attach the file through the cloud file picker.
4. Ask for a variance workbook, and name the file, the tabs, and the sort order you want.
5. Open the workspace panel on the right and watch which skills it loads on its own.

That is twenty minutes and one file, and you will know immediately whether this belongs in your close.

Then do the part that changes your month. Take whatever process you already have written down somewhere, paste it in, and ask Cowork to turn it into a skill file. Schedule it. Go do something else on the third business day.

Every prompt from this walkthrough, plus the monthly variance commentary skill file, is in my AI Library along with the free Finance AI Insider newsletter.