In short: Go to Settings → System → Activation → Change product key, enter your 25-character key and click Activate. If you reinstalled Windows on a PC that was already activated, you usually don't need a key at all: the digital licence activates it automatically once you're online. From the command line, it's slmgr /ipk <key> followed by slmgr /ato. After a motherboard change, use the Activation troubleshooter while signed in to your Microsoft account.

Contents

1. First, check if Windows 11 is already activated
2. Method 1: Enter a product key in Settings
3. Method 2: Enter the key during installation
4. Method 3: Digital licence (automatic activation)
5. Method 4: Command line with slmgr
6. Method 5: Activation troubleshooter after a hardware change
7. Method 6: Upgrade from an activated Windows 10
8. Method 7: OEM key in the firmware
9. Method 8: Business activation (MAK, KMS, Active Directory)
10. Which method should you use?
11. What happens if you don't activate?
12. Why you should avoid "free activators"
13. FAQ

First, check if Windows 11 is already activated

Many PCs are activated without you doing anything. Check first:

1. Open Settings (Win + I).
2. Go to System → Activation.
3. Look at Activation state.

From the command line:

slmgr /xpr

"The machine is permanently activated" means you're done.

Method 1: Enter a product key in Settings

The standard way, and the one most people need.

1. Settings → System → Activation.
2. Next to Change product key, click Change.
3. Enter the 25-character key (XXXXX-XXXXX-XXXXX-XXXXX-XXXXX).
4. Click Next, then Activate.

Make sure you're connected to the internet. Activation usually takes a few seconds.

The key must match your edition. A Pro key won't activate Home, and a Home key won't activate Pro. There's one exception that works in your favour: entering a Pro key on Home upgrades the PC to Pro in place, with no reinstall. Windows installs the extra Pro features, restarts, and activates.

Where's my key? It's in your purchase confirmation email, on the product card, or on a sticker for older PCs. Keys are often entered by copy-paste, so watch for extra spaces at the start or end.

Method 2: Enter the key during installation

When you clean install Windows 11 from a USB drive, setup asks for a product key:

• Have a key? Enter it. Setup then installs the matching edition automatically.
• Don't have it handy? Click "I don't have a product key". You'll be asked to pick an edition. Choose the edition you're licensed for (Home or Pro), then activate later with Method 1 or 3.

Watch out: choosing the wrong edition here is the most common cause of activation errors after a reinstall (0xC004F210, 0xC004F212, 0x803F7001).

Method 3: Digital licence (automatic activation)

A digital licence means Microsoft's activation servers remember your PC's hardware. When you reinstall the same edition on the same PC, Windows activates itself once it's online, with no key needed.

You have a digital licence if your PC:

• came with Windows 11 or Windows 10 pre-installed, or
• was upgraded for free from an activated Windows 10, or
• was activated with a genuine retail key at any point.

Link it to your Microsoft account (do this now)

Linking makes activation much easier to recover after a hardware change:

1. Settings → Accounts → Your info.
2. Click Sign in with a Microsoft account instead (if you use a local account).
3. Go back to Settings → System → Activation. It should now say "…digital license linked to your Microsoft account".

Method 4: Command line with slmgr

Useful for remote sessions, scripts, or when the Settings page won't cooperate. Open Command Prompt or Terminal as administrator:

:: 1. Install the product key
slmgr /ipk XXXXX-XXXXX-XXXXX-XXXXX-XXXXX

:: 2. Activate online
slmgr /ato

:: 3. Confirm
slmgr /xpr

Each command shows a pop-up. To see the output in the console instead (handy over SSH or remote PowerShell):

cscript //nologo %windir%\system32\slmgr.vbs /ato

Replacing a wrong key first (for example, a leftover KMS client key):

slmgr /upk
slmgr /cpky
slmgr /ckms
slmgr /ipk XXXXX-XXXXX-XXXXX-XXXXX-XXXXX
slmgr /ato

PowerShell can activate in one line too:

$svc = Get-CimInstance SoftwareLicensingService
Invoke-CimMethod -InputObject $svc -MethodName InstallProductKey -Arguments @{ ProductKey = 'XXXXX-XXXXX-XXXXX-XXXXX-XXXXX' }
Invoke-CimMethod -InputObject $svc -MethodName RefreshLicenseStatus

Method 5: Activation troubleshooter after a hardware change

Replaced the motherboard? Windows sees it as a new PC and may show 0xC004F211 or 0x803F7001.

1. Sign in with the same Microsoft account your licence is linked to.
2. Settings → System → Activation → Troubleshoot.
3. Choose "I changed hardware on this device recently".
4. Sign in if asked, select "This is the device I'm using right now" from the list, and click Activate.

Not sure which type you have? Run slmgr /dli. The Description line shows RETAIL, OEM or VOLUME.

Method 6: Upgrade from an activated Windows 10

If Windows 10 on your PC is genuinely activated and the hardware meets the Windows 11 requirements, upgrading keeps the activation:

• Windows 10 Home becomes Windows 11 Home
• Windows 10 Pro becomes Windows 11 Pro

Go to Settings → Update & Security → Windows Update on Windows 10 and accept the Windows 11 upgrade, or run Microsoft's Installation Assistant. No key is needed. The licence converts to a digital licence for Windows 11.

Still on Windows 10? Microsoft extended free consumer security updates (ESU) to 12 October 2027, so there's time, but the upgrade itself costs nothing if your PC qualifies.

Method 7: OEM key in the firmware

Most laptops and branded desktops have a Windows key stored in the UEFI firmware. Windows reads it automatically during setup and activates, as long as you install the matching edition.

Check what's stored:

Get-CimInstance SoftwareLicensingService |
  Select-Object OA3xOriginalProductKey, OA3xOriginalProductKeyDescription

• Core in the description means the key is for Home.
• Professional means it's for Pro.

If the firmware key is Home but you want Pro, install Home first (so it activates), then upgrade with a Pro key using Method 1.

Method 8: Business activation (MAK, KMS, Active Directory)

For organisations with Microsoft volume licensing:

Work laptops showing "activated using your organization's activation service" are on KMS or AD-based activation. Connect to the office network or VPN now and then to keep them activated.

Which method should you use?

What happens if you don't activate?

Windows 11 keeps working, but:

• An "Activate Windows" watermark appears in the bottom-right corner.
• Personalisation is locked: wallpaper, colours, themes, lock screen and taskbar settings.
• Reminders show up in Settings and notifications.
• You're not licensed to use it under Microsoft's terms.

Security updates still install, so an unactivated PC isn't cut off. But for a PC you actually use, activation is the right call.

Why you should avoid "free activators"

Scripts and tools that promise free activation usually work by:

• installing a KMS client key and pointing your PC at an unknown KMS server, or
• patching system files.

The problems:

• Security risk: many contain malware, and you're giving an unknown script admin rights.
• It's unlicensed: the PC isn't legally activated.
• It breaks later: expect 0xC004F074 errors, a returning watermark, or problems after major updates.

Check whether a PC has been "activated" this way:

slmgr /dlv

If you see VOLUME_KMSCLIENT and a KMS machine name you don't recognise on a home PC, clean it up with slmgr /upk, slmgr /cpky, slmgr /ckms, then activate properly with Method 1.

Activation failed? Quick fixes

The full list of codes and fixes is in Windows Activation Error Codes: Complete List With Fixes, or paste any code into the free activation error code lookup.

Microsoft references:

• Get help with Windows activation errors (Microsoft Support)
• Slmgr.vbs options (Microsoft Learn)

FAQ

Do I need a product key to activate Windows 11?

Not always. If the PC already has a digital licence (pre-installed Windows, a free upgrade from Windows 10, or an earlier activation), it activates automatically. You only need a key for a new licence or a different edition.

Can I use a Windows 10 key to activate Windows 11?

Yes. Genuine Windows 10 Home and Pro keys activate the same edition of Windows 11.

How do I upgrade Windows 11 Home to Pro?

Go to Settings → System → Activation → Change product key and enter a Windows 11 Pro key. Windows upgrades in place, keeps your files and apps, and restarts once.

How long can I use Windows 11 without activating?

There's no hard time limit. Windows keeps running with the watermark and locked personalisation, but it isn't properly licensed.

Does Windows 11 activation work offline?

Retail and OEM activation need an internet connection. If you can't get online, contact Microsoft support. Business PCs can use KMS on the local network.

Can I activate one key on two PCs?

No. A retail key is licensed for one PC at a time. To move it, deactivate it on the old PC first (slmgr /upk), then activate it on the new one.

Does this work on Windows 11 26H2?

Yes. All of these methods work the same on every current version, including 26H2 (released September 2026).

Ran into an activation problem that isn't covered here? Share the error code and your Windows edition in the comments.

In short: Press Win + R, type winver and press Enter. The window shows your Windows 11 version (for example 25H2) and OS build (for example 26200.xxxx). The first five digits of the build tell you the version: 26200 = 25H2, 26100 = 24H2, 22631 = 23H2. For scripts, use PowerShell: Get-ComputerInfo -Property OSDisplayVersion, OsBuildNumber.

Contents

1. Version vs build vs edition: what's the difference?
2. Method 1: winver (fastest)
3. Method 2: Settings → About
4. Method 3: Command Prompt (ver and systeminfo)
5. Method 4: PowerShell
6. Method 5: Registry (for scripts and inventory)
7. Windows 11 build number to version table
8. Bonus: check many PCs at once
9. FAQ

Version vs build vs edition: what's the difference?

People mix these up all the time, so here's the quick version:

A full build number like 10.0.26200.9278 breaks down as:

10   . 0     . 26200  . 9278
major  minor   build    revision (UBR)

• 26200 is the base build, which tells you the version (25H2).
• 9278 is the revision, which goes up with every monthly cumulative update.

So two PCs on 25H2 can show different builds. One of them just has newer updates.

Why it matters: Microsoft support dates are tied to the version. Windows 11 24H2 Home and Pro stopped getting security updates in October 2026, so if winver shows 24H2 on a Home or Pro PC, it's time to update to 25H2.

Method 1: winver (fastest)

1. Press Win + R.
2. Type winver and press Enter.

A small "About Windows" window opens showing:

Microsoft Windows
Version 25H2 (OS Build 26200.xxxx)

It also shows the licensed edition at the bottom ("licensed to…"). That's it, and it takes three seconds.

Method 2: Settings → About

1. Open Settings (Win + I).
2. Go to System → About.
3. Scroll to Windows specifications.

You'll see:

There's a Copy button next to it, which is handy for pasting into a support ticket.

Method 3: Command Prompt (ver and systeminfo)

Quick: ver

ver

Output:

Microsoft Windows [Version 10.0.26200.xxxx]

Yes, it says 10.0 even on Windows 11. That's normal. Windows 11 kept the 10.0 kernel version number, and the build is what separates them: any build 22000 or higher is Windows 11.

Detailed: systeminfo

systeminfo | findstr /B /C:"OS Name" /C:"OS Version"

Output:

OS Name:     Microsoft Windows 11 Pro
OS Version:  10.0.26200 N/A Build 26200

This gives you the edition and build in one go, but not the "25H2" label. Use the table below to map it.

Method 4: PowerShell

The cleanest option for scripts:

Get-ComputerInfo -Property OsName, OSDisplayVersion, OsBuildNumber

Output:

OsName                   OSDisplayVersion OsBuildNumber
------                   ---------------- -------------
Microsoft Windows 11 Pro 25H2             26200

Get-ComputerInfo can take a few seconds because it collects a lot of data. For a faster check, use CIM:

Get-CimInstance Win32_OperatingSystem | Select-Object Caption, Version, BuildNumber

Method 5: Registry (for scripts and inventory)

Everything above ultimately reads from this key:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion

Read it with PowerShell:

Get-ItemProperty 'HKLM:\SOFTWARE\Microsoft\Windows NT\CurrentVersion' |
  Select-Object EditionID, DisplayVersion, CurrentBuild, UBR

Output:

EditionID    DisplayVersion CurrentBuild UBR
---------    -------------- ------------ ----
Professional 25H2           26200        9278

To build the full version string:

$cv = Get-ItemProperty 'HKLM:\SOFTWARE\Microsoft\Windows NT\CurrentVersion'
"$($cv.DisplayVersion) (OS Build $($cv.CurrentBuild).$($cv.UBR))"
# 25H2 (OS Build 26200.9278)

Gotcha: The ProductName value in this key still says "Windows 10 Pro" on many Windows 11 machines. Don't use it to detect Windows 11. Check CurrentBuild -ge 22000 instead:

$build = [int](Get-ItemProperty 'HKLM:\SOFTWARE\Microsoft\Windows NT\CurrentVersion').CurrentBuild
if ($build -ge 22000) { 'Windows 11' } else { 'Windows 10' }

Windows 11 build number to version table

Match the first five digits of your build:

A note on 26H1: it has the highest number, but Microsoft only ships it pre-installed on specific new hardware. Existing 24H2/25H2 PCs won't get it through Windows Update, so don't worry if you don't see it.

For the latest revision numbers and KB articles, Microsoft keeps an official list on the Windows 11 release information page.

If you'd rather paste a build number and get the version, release date and support status back, I use this free Windows & Office build number lookup. It also covers Office builds, which are much harder to decode.

Bonus: check many PCs at once

If you manage a few machines with PowerShell remoting enabled:

$computers = 'PC-01', 'PC-02', 'PC-03'

Invoke-Command -ComputerName $computers -ScriptBlock {
  $cv = Get-ItemProperty 'HKLM:\SOFTWARE\Microsoft\Windows NT\CurrentVersion'
  [pscustomobject]@{
    Edition = $cv.EditionID
    Version = $cv.DisplayVersion
    Build   = "$($cv.CurrentBuild).$($cv.UBR)"
  }
} | Select-Object PSComputerName, Edition, Version, Build |
  Format-Table -AutoSize

Add | Export-Csv .\windows-versions.csv -NoTypeInformation to save it as a spreadsheet. That's a quick way to spot machines still on 24H2 that need updating.

FAQ

How do I know if I have Windows 10 or Windows 11?

Run winver. If the build is 22000 or higher, it's Windows 11. Builds starting with 19041–19045 are Windows 10.

Why does Command Prompt say "Version 10.0" on Windows 11?

Windows 11 kept the internal version number 10.0 for app compatibility. The build number is what tells them apart.

What is the latest Windows 11 version?

For existing PCs, 25H2 (build 26200) is the current feature release. Version 26H1 (build 28000) exists but only ships on certain new devices.

How do I update to the latest version?

Go to Settings → Windows Update and click Check for updates. If 25H2 is available for your PC, it appears as a feature update. Going from 24H2 to 25H2 is a small enablement package and installs quickly.

Does the build number tell me if Windows is activated?

No. To check activation, go to Settings → System → Activation, or run slmgr /xpr in an admin Command Prompt. If you're seeing an activation error, I wrote a full guide: Windows Activation Error Codes: Complete List With Fixes.

Where can I see what changed in each build?

Every build on Microsoft's Windows 11 release information page links to its KB article, which lists the fixes and changes in that update.

Which build are you on right now? Drop it in the comments. I'm curious how many people are still on 24H2.