Grammarly vs. Microsoft Copilot: do you need both?

The question every IT team is asking

If your company already pays for Microsoft 365 and recently added Copilot licenses, someone on your team has asked: "Do we still need Grammarly?"

It is a fair question. Both tools help people write better. Both sit inside the applications where work happens. And at $25 per user per month for Grammarly Business and $30 per user per month for Copilot, running both across a 500-person organization costs $330,000 annually.

This article breaks down what each tool actually does, where they overlap, and how to make a data-informed decision for your organization.

What each tool covers

Grammarly Business

Grammarly started as a grammar and spelling checker and evolved into a broader writing assistant. Its core capabilities:

• Grammar, spelling, and punctuation correction across virtually every text input (email, browser, desktop apps)
• Tone detection and adjustment. Grammarly analyzes the tone of your writing (confident, friendly, formal) and suggests adjustments. This works at the document level, not just sentence by sentence.
• Style guide enforcement. Grammarly Business lets admins set company-specific style rules (brand voice, terminology, banned phrases) that apply across all users.
• Rewrite suggestions. Full sentence and paragraph rewrites for clarity, conciseness, or tone.
• Cross-platform coverage. Grammarly works in browsers, desktop apps, mobile keyboards, and integrates with Slack, Gmail, Google Docs, and Microsoft 365.

Microsoft Copilot

Copilot is an AI assistant embedded across the Microsoft 365 suite. Its writing-related capabilities:

• Draft generation. Copilot can generate first drafts of emails, documents, and presentations from prompts.
• Summarization. Summarize long email threads, meeting transcripts, documents, and Teams chats.
• Rewrite and tone adjustment. Copilot can rewrite selected text to be more formal, concise, or casual.
• Basic grammar and spelling. Microsoft Editor (included with M365) handles grammar and spelling, and Copilot builds on this foundation.
• Data integration. Copilot can pull data from your Microsoft Graph (emails, files, calendar, Teams) to generate contextually relevant content.
• Presentation and spreadsheet assistance. Copilot works across Word, Outlook, PowerPoint, Excel, and Teams.

Where Copilot falls short

Despite Copilot's broad capabilities, there are specific areas where Grammarly still provides meaningfully better results:

Document-level tone analysis

Grammarly evaluates tone across an entire document and provides a tone score. Copilot can adjust tone for selected passages, but it does not give you a holistic view of how your document reads from start to finish. For teams that care about consistent brand voice across customer-facing content, this distinction matters.

Style guide enforcement at scale

Grammarly Business allows admins to define company-wide style rules: preferred terminology, banned words, tone guidelines, and formatting standards. These rules apply automatically across every user and every platform. Copilot does not have an equivalent feature. You can prompt Copilot to follow a style guide, but there is no centralized enforcement mechanism.

Cross-platform consistency

Grammarly works everywhere text is entered: Chrome, Safari, Slack, Gmail, Google Docs, Microsoft 365, desktop apps, and mobile. Copilot is limited to the Microsoft 365 ecosystem. If your team writes in Google Workspace, Slack, or Notion alongside Microsoft tools, Grammarly provides coverage that Copilot cannot.

Passive, always-on correction

Grammarly runs in the background and flags issues as you type. Copilot requires active invocation. You ask it to rewrite something, and it does. But it will not underline a grammatical error in real time the way Grammarly does. Microsoft Editor handles some of this, but its coverage is narrower than Grammarly's.

Where Grammarly is redundant

In a Copilot environment, several Grammarly features become duplicative:

Basic grammar and spelling

If your team works primarily in Microsoft 365, the combination of Microsoft Editor and Copilot covers grammar, spelling, and punctuation correction adequately. Grammarly's advantage here is marginal for most business writing.

Email drafting and rewriting

Copilot in Outlook can draft, rewrite, and adjust tone for emails. If email is the primary writing surface, Grammarly's rewrite capabilities overlap significantly with what Copilot already provides.

Summarization

Grammarly recently added summarization features, but Copilot's summarization is deeper because it has access to your Microsoft Graph. Copilot can summarize a meeting you missed by pulling the transcript from Teams. Grammarly can only summarize text you paste into it.

How to evaluate for your organization

The answer to "do we need both?" depends on three factors specific to your environment.

1. Check feature overlap

Map the features your team actually uses in Grammarly against what Copilot provides. Most organizations find that 60 to 70% of Grammarly usage falls into grammar correction and basic rewriting, both of which Copilot and Microsoft Editor handle.

The remaining 30 to 40% (tone analysis, style guide enforcement, cross-platform coverage) is where Grammarly may still add unique value.

2. Check utilization

Pull your Grammarly usage data. How many licensed users are active monthly? What features are they using?

A common finding: companies with 500 Grammarly seats discover that only 180 are active monthly, and of those, 120 use it only for basic grammar correction. That means only 60 users rely on Grammarly's differentiated features. At $25 per seat per month, you are paying $150,000 annually for 60 power users and 440 seats that are either unused or redundant with Copilot.

3. Check integration depth

Where does your team write?

• Primarily Microsoft 365: Copilot likely covers your needs. Grammarly's value is limited to style guide enforcement and tone scoring.
• Mixed environment (Microsoft + Google + Slack + other tools): Grammarly's cross-platform coverage fills gaps that Copilot cannot reach.
• Customer-facing content teams: If you have marketing, support, or documentation teams that need consistent brand voice enforcement, Grammarly's style guide feature is difficult to replicate with Copilot.

Worked example: a 500-person company

In this scenario, the company keeps Grammarly only for the 75 users who rely on style guide enforcement and cross-platform coverage. Everyone else uses Copilot and Microsoft Editor for grammar, rewriting, and drafting.

The savings of $127,500 annually come entirely from right-sizing Grammarly, not from eliminating it.

The broader pattern: AI tool overlap

This Grammarly vs. Copilot question is just one example of a pattern playing out across every SaaS portfolio. As AI capabilities get embedded into platform tools (Microsoft 365, Google Workspace, Salesforce), standalone AI tools that were purchased separately start to overlap.

Other common overlaps mid-market teams should evaluate:

• Otter.ai or Fireflies.ai vs. Copilot (meeting transcription and summarization)
• Jasper or Writer vs. Copilot (marketing content generation)
• Beautiful.ai vs. Copilot in PowerPoint (presentation design)
• ChatGPT Team vs. Copilot (general-purpose AI assistant)

Each of these follows the same evaluation framework: check feature overlap, check utilization, check integration depth.

StackIQ's AI replacement analysis automates this evaluation by mapping your current tool portfolio against the AI capabilities embedded in your platform licenses. It identifies which standalone tools are fully replaceable, which are partially redundant, and which still provide unique value.

Making the decision

The answer is rarely "keep everything" or "cut everything." For most mid-market companies, the right answer is:

1. Keep Copilot for the broad user base (it covers drafting, rewriting, summarization, and basic grammar)
2. Right-size Grammarly to the teams that use its differentiated features (style guides, tone analysis, cross-platform coverage)
3. Reassess in 6 months as both products continue to evolve

The key is making this decision with data rather than assumptions. Pull utilization, map feature overlap, and let the numbers guide the conversation.

If you are evaluating AI tool overlap across your SaaS portfolio, see how StackIQ identifies which tools AI can replace and which ones still earn their seat.