Choosing between Office 2021 Professional Plus and Office 365 (now branded as Microsoft 365) can feel like picking between two versions of the same thing. Both give you Word, Excel, PowerPoint, and Outlook. Both are “Microsoft Office.” And both will handle everyday productivity just fine.

But here’s the truth: these products are built for different types of users. One is a one-time purchase designed for stable, offline work. The other is a subscription built for always-updated apps, cloud collaboration, and growing AI features. Once you understand those core differences, the right choice gets a lot easier.

This guide compares Office 2021 Pro Plus and Microsoft 365 in plain English—pricing, features, updates, devices, AI tools, and long-term value—so you can buy what actually fits your workflow.

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What Is Office 2021 Professional Plus?

Office 2021 Professional Plus is a perpetual-license edition. You pay once, install it on a Windows PC, and keep using that specific version indefinitely. It’s usually sold through volume licensing for organizations, but it’s also widely purchased by individuals who want a “lifetime” desktop suite without ongoing fees. Microsoft Learn+2Microsoft+2

What you get in Office 2021 Pro Plus

• Word 2021
  
• Excel 2021
  
• PowerPoint 2021
  
• Outlook 2021
  
• OneNote (desktop)
  
• Publisher 2021
  
• Access 2021
  
• Teams (classic, included in many Pro Plus SKUs) Microsoft Learn+1
  

You receive security updates, but you don’t get major new features after purchase. Office 2021 stays “frozen” as that version.

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What Is Office 365 / Microsoft 365?

Office 365 was renamed Microsoft 365 to reflect that it’s more than just Office apps. It’s a subscription service that includes desktop apps, mobile apps, web apps, cloud storage, and continuous feature updates. How-To Geek+2Microsoft+2

What you get in Microsoft 365

• Always-latest Word, Excel, PowerPoint, Outlook, OneNote
  
• Premium extras depending on plan (e.g., Access, Publisher on PC)
  
• 1 TB OneDrive storage per user (Personal/Family)
  
• Deep cloud collaboration features
  
• Growing AI/Copilot tools (plan-dependent) How-To Geek+2Microsoft+2
  

You pay monthly or yearly, and as long as you keep the subscription active, you keep getting new features.

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Pricing and Long-Term Cost

This is the first big fork in the road.

Office 2021 Pro Plus cost model

• One-time payment
  
• No renewal fees
  
• Cost stays the same no matter how long you use it licendi.com+1
  

Microsoft 365 cost model

• Recurring subscription
  
• Price depends on plan (Personal, Family, Business, Enterprise)
  
• Cost grows over time, but you receive ongoing upgrades Microsoft+1
  

A simple way to think about it:

• If you plan to use Office on one PC for 3–6 years and don’t care about new features, Office 2021 is usually cheaper overall.
  
• If you love updates, cloud services, and multi-device access, Microsoft 365 earns its cost through extras. licendi.com+2DS Tech+2
  

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Updates: Stable vs Always New

Office 2021 Pro Plus updates

Office 2021 only gets:

• security patches
  
• bug fixes
  
• small stability improvements
  

It does not receive major new tools, new AI features, or new design systems. licendi.com+1

Microsoft 365 updates

Microsoft 365 gets:

• new features every month
  
• UI enhancements
  
• cloud and collaboration upgrades
  
• newest Excel functions, PowerPoint tools, Outlook improvements, etc. DS Tech+1
  

If you want to stay at the cutting edge, Microsoft 365 is the clear winner. If you want “set it and forget it,” Office 2021 is perfect.

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Devices and Flexibility

Office 2021 Pro Plus licensing

Most perpetual licenses are for:

• one Windows PC
  
• not designed for multiple devices per user licendi.com+1
  

Microsoft 365 licensing

Depends on plan, but generally:

• install on multiple devices (PC, Mac, tablet, phone)
  
• use both desktop and mobile apps
  
• Family plans cover up to 6 people Microsoft+1
  

So:

• One desktop, single user? Office 2021 fits cleanly.
  
• Multiple devices or a whole household/team? Microsoft 365 is built for that.
  

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Cloud Features and Collaboration

Both products can save to OneDrive, but Microsoft 365 makes cloud work feel native.

Microsoft 365 advantages

• real-time co-authoring that’s smoother and faster
  
• easier sharing permissions
  
• deeper version history
  
• web + desktop handoff without friction How-To Geek+1
  

Office 2021 reality

Office 2021 can collaborate in the cloud, but:

• fewer collaborative features
  
• less frequent improvements
  
• designed primarily for offline/local use How-To Geek+1
  

If you work in teams, share docs daily, or edit across devices, Microsoft 365 is the better experience.

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AI and Copilot: The 2025 Difference-Maker

In 2025, AI is becoming the biggest separation between perpetual Office and Microsoft 365.

Microsoft 365 AI

Microsoft is rapidly expanding Copilot AI inside Microsoft 365 apps. New plans like Microsoft 365 Premium bundle deeper Copilot features for writing, spreadsheet analysis, and presentation building. The Verge+1

With AI in Microsoft 365 you can:

• draft and rewrite in Word
  
• generate insights and formulas in Excel
  
• create slide decks with prompts in PowerPoint
  
• summarize inbox threads in Outlook
  

Office 2021 AI

Office 2021 does not include Copilot, and it won’t gain it later. You still get smart basics (spellcheck, some suggestions), but not Copilot-level automation. How-To Geek+1

So if AI productivity is high on your list, Microsoft 365 is the only real option.

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App Lineup and Business Tools

Office 2021 Pro Plus is the “maximum desktop bundle,” especially for Windows business tasks.

Office 2021 Pro Plus edge

• includes Access and Publisher
  
• great for admin teams, small business databases, printed materials, internal tools Microsoft Learn+1
  

Microsoft 365 edge

• includes the same apps (plan-dependent)
  
• plus premium cloud-first services and cross-platform availability Microsoft+1
  

If Access and Publisher matter to you specifically, double-check your Microsoft 365 plan, because not all plans include them by default.

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Which One Should You Choose?

Here’s a straightforward match.

Choose Office 2021 Professional Plus if you:

• want a one-time purchase with no subscription
  
• work mostly offline or on local files
  
• use a single Windows PC
  
• need Access/Publisher for classic desktop workflows
  
• prefer stable software without constant UI changes Microsoft Learn+2licendi.com+2
  

Choose Microsoft 365 if you:

• want always-latest features
  
• collaborate often or work in the cloud
  
• use multiple devices (PC/Mac/phone/tablet)
  
• want Copilot AI and new productivity automation
  
• like bundled OneDrive storage and extra services The Verge+3How-To Geek+3DS Tech+3
  

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Final Verdict

There’s no universal winner—only a better fit for how you work.

• Office 2021 Pro Plus is the best choice for users who want a powerful desktop suite, own it outright, and keep costs predictable for years.
  
• Microsoft 365 is the best choice for users who want continuous innovation, multi-device flexibility, cloud collaboration, and AI baked into daily work.