What you need before you start

Microsoft 365 (formerly called Office 365) is a subscription service that gives you access to Word, Excel, PowerPoint, Outlook, and other programs. Before you install it, you need a Microsoft account, an active subscription, and enough space on your computer — typically 4 GB of free disk space for Windows or 10 GB for Mac.

You can buy a Microsoft 365 subscription directly from Microsoft's website, through retailers like Best Buy or Amazon, or sometimes through your employer or school. Each subscription includes a product key or login credentials that you'll use during installation. If you already have a Microsoft account from using Outlook.com, OneDrive, or another Microsoft service, you can use that same account.

Check your computer's operating system before you begin. Microsoft 365 works on Windows 10 and newer, or Mac OS 10.10 and newer. If your computer is older, you may not be able to install the current version.

Key Takeaways

  • You need a Microsoft account and an active subscription before installation begins, whether you bought it yourself or received it through work or school.
  • On Windows, you download the installer from Microsoft's website, sign in with your account, and let the installer finish — the whole process usually takes 15 to 30 minutes.
  • On Mac, the process is similar: download from the website, open the installer, and drag Microsoft 365 to your Applications folder.
  • After installation, open any Microsoft 365 program and sign in with your account to activate your subscription and start using it.
  • If installation fails or programs won't open, restarting your computer and checking your internet connection fixes most problems.

Installing on Windows

Go to account.microsoft.com and sign in with the Microsoft account tied to your subscription. Click "Install Office" or "Install Microsoft 365" — the exact wording depends on your subscription type. You'll see a button that says "Install" or "Download". Click it to download the installer file to your computer, usually to your Downloads folder.

Once the download finishes, open your Downloads folder and double-click the installer file (it will be named something like "OfficeSetup.exe"). A window will open asking you to allow the installer to make changes to your computer — click "Yes". The installer will then download the programs you need and install them automatically. This can take 15 to 30 minutes depending on your internet speed.

When the installer finishes, you'll see a message saying the installation is complete. You can now open any Microsoft 365 program from your Start menu — search for "Word", "Excel", "Outlook", or whichever program you need. The first time you open a program, it will ask you to sign in with your Microsoft account. Enter your email and password, and the program will activate your subscription.

Installing on Mac

Sign in to account.microsoft.com with your Microsoft account. Click "Install Office" or "Install Microsoft 365" and then click "Download". The installer file will download to your Downloads folder — it's usually named "Microsoft_Office_16.X.pkg" or similar.

Open your Downloads folder and double-click the installer file. A window will open showing the Microsoft 365 programs and asking you to agree to the license terms. Read through the terms if you want, then click "Continue" and "Agree". The installer will ask where you want to install Microsoft 365 — the default location (your Applications folder) is fine for most people. Click "Install" and enter your Mac password when prompted.

The installation usually takes 10 to 20 minutes. When it finishes, you'll see a message confirming the installation is complete. Open your Applications folder, find Microsoft Word or another Microsoft 365 program, and double-click it to open it. Sign in with your Microsoft account the first time you open any program, and your subscription will activate.

Signing in and activating your subscription

After installation, open any Microsoft 365 program — Word, Excel, Outlook, or PowerPoint. A sign-in screen will appear. Enter the email address and password for the Microsoft account that has your subscription. If you're not sure which account has your subscription, check your confirmation email from when you bought it or check account.microsoft.com.

After you sign in, the program will activate your subscription automatically. You should see your name or email in the top right corner of the program window, and you'll have full access to all features. If the program says your subscription has expired or is not found, sign out and sign back in, or restart your computer and try again.

If you share your computer with other people, each person can sign in with their own Microsoft account. Each account gets its own separate Microsoft 365 subscription if they have one, or they can use a shared family subscription if you set one up.

Troubleshooting installation problems

If the installer won't start or keeps stopping, restart your computer and try downloading the installer again. Make sure you have at least 4 GB of free disk space (check by right-clicking your C: drive on Windows or clicking the Apple menu and selecting "About This Mac" on Mac). Close any other programs running in the background, especially antivirus software, which can sometimes block the installer.

If a program won't open after installation, restart your computer first — this fixes most problems. If it still won't open, go back to account.microsoft.com, click "Install Office", and run the installer again. You can reinstall over an existing installation without losing anything.

If you see an error message during installation, write down the error code and search for it on Microsoft's support website (support.microsoft.com). Error codes usually point to specific problems like a bad internet connection, a corrupted download, or a conflict with another program on your computer.

Uninstalling Microsoft 365

On Windows, go to Settings, click "Apps", then "Apps and Features". Search for "Microsoft 365" or "Office", click it, and click "Uninstall". Follow the prompts to remove it from your computer. On Mac, open your Applications folder, find the Microsoft 365 programs, and drag them to the Trash. Empty the Trash to complete the removal.

Uninstalling removes the programs from your computer but does not cancel your subscription. If you want to stop paying for Microsoft 365, you need to cancel your subscription separately at account.microsoft.com under "Subscriptions" or "Billing".

Frequently Asked Questions

Can I install Microsoft 365 on more than one computer?

Yes. Most Microsoft 365 subscriptions let you install on up to five devices and use it on up to five devices at the same time. Sign in with the same Microsoft account on each computer, and each one will have access to your subscription. Check your subscription details at account.microsoft.com to see your device limit.

Do I need internet to use Microsoft 365 after I install it?

You need internet to sign in the first time and to activate your subscription. After that, you can use Word, Excel, and PowerPoint offline. Outlook and other programs that sync with the cloud work better with internet, but you can still read and compose emails offline.

What if I don't have a product key?

You don't need a product key for modern Microsoft 365 subscriptions. Just sign in with your Microsoft account at account.microsoft.com and download the installer from there. Older versions of Office used product keys, but the current version uses your account instead.

Can I use Microsoft 365 on a tablet or phone?

Yes, but you download the apps from the App Store (iPhone or iPad) or Google Play (Android) instead of installing from a website. Search for "Microsoft Word", "Microsoft Excel", or "Microsoft Outlook" in your device's app store, download the app, and sign in with your Microsoft account. Some features may be limited on mobile compared to the desktop version.

Why does the installer keep asking for my password?

The installer needs your computer's administrator password to make changes to your system. This is a security feature. Enter your password when prompted. If you don't know your password, you may need to contact whoever set up your computer or your IT department if it's a work computer.