If your firm already runs on Microsoft 365, you've probably had the Copilot upsell land in your inbox more than once. And most of your team has quietly been using ChatGPT for the past year or two. So the practical question isn't whether to use AI — it's which tool you should actually be paying for, and for what.
This is an honest comparison written for firms that are already on the Microsoft stack. No hype. We'll cover where Copilot's integration genuinely wins, where ChatGPT gives you more for your money, and the situations where the real answer is neither — you need a workflow tool instead.
The short version
Copilot and ChatGPT are both large-language-model assistants, and for pure writing and reasoning they're broadly comparable. The difference that matters for an accounting firm isn't the quality of the prose — it's where the tool sits.
- Microsoft Copilot lives inside Outlook, Word, Excel, Teams and SharePoint, and can see your firm's own data (emails, documents, spreadsheets) under your existing Microsoft security and compliance settings.
- ChatGPT lives in a browser tab or app. It's a blank, powerful assistant that knows nothing about your firm unless you paste it in — but it's cheaper, more flexible, and often faster to adopt.
Neither is built to run a repeatable process end to end. That's the third category, and it's the one most firms overlook.
Where Microsoft Copilot wins
Copilot's advantage is context. Because it's plumbed into Microsoft Graph, it can reference the material your firm already holds without anyone copying and pasting.
1. Summarising long email threads and Teams meetings
Copilot in Outlook can summarise a 40-message client thread into a few dot points, and Copilot in Teams can produce meeting notes and action items automatically. For a practice manager triaging a busy inbox on Monday morning, that's genuinely useful and hard to replicate with a browser-based tool.
2. Working inside documents you already have
"Draft an engagement letter based on the last three we sent this client" is the kind of instruction Copilot can act on because it can read your SharePoint and OneDrive. ChatGPT can't — you'd have to feed it the source material each time.
3. Data governance and residency
This is the one that matters most for accountants handling client tax file numbers, financials and identity documents. Copilot operates within your Microsoft 365 tenant, honours your existing permissions, and Microsoft's commercial data protection terms mean your prompts and firm data aren't used to train the underlying models. If your firm has strict obligations under the Privacy Act and your professional body's standards, that inheritance of your existing controls is a real advantage.
4. Excel work — with a caveat
Copilot in Excel can explain formulas, suggest formulas, and analyse a table you point it at. It's helpful for exploring a dataset. Just don't mistake it for a reconciliation engine — it's an assistant, not an auditor, and you still check its output.
Where ChatGPT wins
ChatGPT's advantages are cost, flexibility and the pace of new features.
1. Price and licensing flexibility
Copilot is licensed per user per month on top of your existing Microsoft 365 subscription, and it's a meaningful jump. ChatGPT's paid tiers are cheaper per seat, and you can give it to only the three people who'll actually use it heavily rather than licensing the whole firm. For a small practice testing the water, that lower commitment matters.
2. Raw capability and custom GPTs
ChatGPT tends to get new model capabilities first, and its custom GPT feature lets you build a purpose-specific assistant — say, a "BAS query responder" loaded with your standard explanations, or a "file note drafter" with your firm's tone baked in. You can share these across the team. We've written about this style of task-level automation in AI for Accountants: 5 Admin Tasks You Can Automate With ChatGPT.
3. Prompt-heavy, repeatable drafting
If your use case is "write me a clear client email explaining why their refund is lower this year" or "turn these rough notes into a professional file note," ChatGPT does this beautifully and you don't need it to see your firm's data to do it. The same applies to research-style drafting where a clean, standalone assistant is actually easier to control.
4. Experimentation without touching your tenant
Because ChatGPT sits outside your Microsoft environment, staff can experiment freely — provided you set the rules. Which brings us to the important caveat.
Never paste client-identifying data, tax file numbers, or confidential financials into a consumer ChatGPT account. Use a business/team tier with data controls turned off for training, and write a one-page staff policy on what is and isn't allowed. This is non-negotiable for an accounting firm.
A side-by-side summary
| Factor | Microsoft Copilot | ChatGPT |
|---|---|---|
| Sees your firm's emails/docs | Yes, within your tenant | No — you paste context in |
| Data governance | Inherits your M365 controls | Depends on tier and settings |
| Cost per seat | Higher, added to M365 | Lower, licence who you want |
| Best at | In-context work across Office apps | Flexible drafting, custom assistants |
| Setup effort | Admin config, tenant-wide | Near-instant per user |
| New features first | Slower rollout | Usually earlier |
How to choose for your firm
Rather than picking a winner in the abstract, match the tool to your actual bottleneck.
- If your pain is email and document overload and you're already deep in Microsoft 365, Copilot's context is worth the premium — start with a handful of licences for the partners and practice manager who live in Outlook.
- If your pain is drafting and repetitive writing — client emails, file notes, first-draft advice — ChatGPT on a business tier gives you more capability per dollar and lets you build reusable custom assistants.
- If your team is nervous about AI generally, ChatGPT's low-commitment licensing is a gentler, cheaper way to build confidence before you commit the whole firm to Copilot.
Plenty of firms end up running both: Copilot for a few heavy Office users, ChatGPT for broader drafting. That's a perfectly sensible answer.
When you need neither — and this is the important part
Here's the trap. Both Copilot and ChatGPT are assistants. They wait for a human to prompt them, help with a single task, then stop. They don't run a process. And most of the time a partner loses isn't spent writing — it's spent shuffling information between systems.
Think about supplier invoice handling: an invoice arrives by email, someone reads it, keys the details into your accounting software, files the PDF, and flags anything odd for approval. No amount of clever prompting inside Word makes that happen automatically. What you need is a workflow — a chain of steps that runs without anyone starting it. We walk through exactly this kind of end-to-end automation in our case study on eliminating human error in supplier invoice handling.
The same is true of client intake, deadline reminders, document requests, and onboarding. These are process problems, not writing problems. The tools that solve them are automation platforms like Zapier and Make, often with an AI step slotted in for the part that needs judgement or drafting. Our piece on what admin work you should automate before hiring another staff member is a good starting point for spotting which of your tasks fall into this category.
A useful way to think about it:
- Copilot / ChatGPT = help me do a task faster.
- Workflow tools (Zapier, Make + AI) = do this task for me, every time, without asking.
The firms getting the biggest return aren't the ones who simply bought the more expensive AI licence. They're the ones who separated their "help me write this" problems from their "this happens 40 times a week" problems — and used the right tool for each.
The practical next step
Before you commit to Copilot across the firm or roll out ChatGPT to everyone, spend a week writing down the tasks that actually eat your team's time. You'll quickly see which are drafting tasks (an assistant helps) and which are repetitive processes (a workflow helps). That single list will save you from paying for the wrong tool.
If you'd like a head start, our free guide, 10 AI Workflows to Save 10+ Hours a Week, lays out the specific, repeatable processes accounting firms are automating right now — the ones neither Copilot nor ChatGPT will run for you on their own. It's a practical place to begin before you spend a dollar on licences.
Want these ideas working in your firm? We build controlled AI workflows for Australian professional services firms — starting with a free automation audit.