The Complete Guide to Windows Licensing in 2026

What a Windows Licence Actually Is

A Windows licence is a legal right to install and use Windows on a device. That’s it. The installation media, the ISO, and the product key are not the licence. They’re the delivery mechanism and the activation trigger. The licence is the underlying entitlement.

This distinction matters because it’s where most purchasing mistakes happen. People conflate the key with the licence, assume that because a key activates it must be legitimate, and miss the question they should be asking: what type of licence is behind this key, and does it permit what I’m doing with it?

OEM, Retail, and Volume: The Three Licence Types

Every Windows licence is one of three types. Understanding which one you have — or are buying — determines what you can do with it.

OEM

OEM licences ship with new hardware. When you buy a laptop or pre-built PC with Windows included, the licence is OEM. It’s cheaper than retail because it comes with a condition: it’s tied to the device it’s first activated on. Not just the device — the motherboard specifically. If that board is replaced, the licence typically doesn’t follow.

The binding is tighter than most people assume. On many systems, replacing the motherboard invalidates an OEM licence even if everything else stays the same. Upgrading RAM or adding storage has no effect on activation. The motherboard is the identity of an OEM-licensed machine, and that’s a firm line.

Retail

Retail licences are purchased independently of hardware and can be transferred between machines. If you build a new PC and want to bring your licence across, retail is the right type. The transfer process involves deactivating on the old machine and activating on the new one — linking the key to a Microsoft account first makes this significantly smoother. Without account linkage, reactivation after a major hardware change can require a phone call to Microsoft.

For anyone buying from a reseller, retail is the correct type to confirm before purchasing. It’s not always the type you get if you don’t ask.

Volume

Volume licences are designed for organisations: businesses, schools, government. They use entirely different activation systems (covered below), are managed centrally, and are not intended for individual resale. A single volume key can activate hundreds of machines. That commercial arrangement is the source of much of the grey market — keys from volume agreements appearing in retail channels at unusually low prices.

Volume licensing can be entirely legitimate and perpetual when used within its intended context. The problems arise when keys leave that context.

If you’re buying for personal use, retail is the appropriate type. Not sure which edition you need? See our Windows 11 Home vs Pro comparison or use the Windows 11 edition adviser.

Product Key vs Digital Licence

A product key is the 25-character code used to activate Windows. It starts the process. A digital licence (sometimes called a digital entitlement) is what gets created after that — an activation record stored on Microsoft’s servers, linked to your hardware ID and optionally to your Microsoft account.

Once a digital licence exists, Windows can often reactivate itself after a reinstall without you entering the key again. The licence is already associated with the hardware. This is why Microsoft account linkage matters: if the digital licence is tied to an account, you can restore it across hardware changes through the Activation Troubleshooter. Without that linkage, the licence is bound to the hardware alone.

MAK and KMS: Why Some Keys Fail Months After Activation

This is the section that explains most activation failures in the secondary market. Volume licences use one of two activation systems: MAK or KMS. Understanding the difference explains why a key can appear to work perfectly, then deactivate months later with no warning.

MAK (Multiple Activation Key)

A MAK key has a fixed number of activations. Each time it’s used, the counter decrements. Once the pool is exhausted, the key stops activating new machines. Activation itself is permanent — machines already activated stay activated as long as they don’t require reactivation. The risk is buying a MAK key where the remaining activation count is low or unknown.

KMS (Key Management Service)

KMS is the mechanism behind most delayed activation failures, and it’s worth understanding exactly how it works. In a corporate environment, activation doesn’t go directly to Microsoft — it goes to a local KMS server run by the organisation. Each activated machine must check back in with that server every 180 days to renew its activation. If the machine can’t reach the server, activation eventually lapses.

When KMS keys leak into the secondary market, they may activate against the original server initially. But that server isn’t maintained forever. When it goes offline — or when the key is revoked — any machine activated against it stops renewing. The result is a machine that was genuinely activated for months, then suddenly isn’t. This is not a hypothetical risk. It’s the specific failure mode behind the majority of “the key worked then stopped” complaints.

Hardware Changes and Activation

The motherboard is the core hardware identity of a Windows-licensed machine. This affects OEM licences directly and retail licences indirectly.

With an OEM licence, replacing the motherboard typically invalidates the licence. Windows will report activation failure and reactivation is not guaranteed — the licence was sold as part of that specific hardware configuration. Upgrading RAM, replacing storage, or adding a GPU has no effect on OEM activation. The motherboard is the only component that consistently triggers it.

With a retail licence, a motherboard change is recoverable. Go to Settings → System → Activation → Troubleshoot and select the option indicating you recently changed hardware. If the licence is linked to a Microsoft account, this process is usually straightforward. Without account linkage, it may require a phone call to Microsoft’s activation support line. For a full walkthrough, see our guide on transferring a Windows licence to a new PC.

Volume licences depend on the activation method. A MAK-activated machine consumes another activation on reactivation. A KMS-activated machine re-contacts the server as normal, assuming the server is still accessible.

Why Keys Fail Activation

Activation failures have specific causes. Most can be traced to one of these:

• Edition mismatch. A Home key cannot activate Pro, and vice versa. The key is edition-specific.
• Region restriction. Some keys are issued for specific geographic markets and won’t activate outside them.
• KMS server unavailability. As described above: the key was valid, the server is now gone.
• MAK pool exhausted. The key has used all its activations. Further activations are refused.
• MSDN or developer keys. These look identical to retail keys — same format, same length — but are issued under subscription agreements not meant for resale. They activate, but Microsoft can revoke them. There is no way to identify one from the key string alone.
• Licence not properly transferred. If the previous holder didn’t deactivate before sale, the key may be flagged when used on a second machine simultaneously.

MSDN keys deserve a specific mention. The format is identical to retail. They activate Windows cleanly. The only indicator of the problem is the price at which they were sold and, later, a revocation notice. This is why sourcing from a transparent seller with activation support is not an optional extra.

Buying Safely in 2026

The secondary market for Windows licences is not inherently unsafe. Perpetual retail licences can be legitimately resold and transferred. The risk is concentrated in specific key types — KMS leakage and MSDN keys primarily — and in sellers who offer no transparency about source or support after purchase.

When buying, confirm:

• Edition. Home or Pro. The key is edition-specific and cannot be used across editions.
• Licence type. Retail is the correct type for individual users. Ask if it’s not stated.
• Activation support. If a key fails, a legitimate seller resolves it. No support after purchase is a significant risk signal.
• Price. Retail Windows 11 Pro keys below £20 should prompt questions about key type. The economics of legitimate resale don’t support that pricing.

The legal position on resale is established — the legality of reselling Microsoft licence keys in the UK is covered in full separately. The practical risk sits with key type and seller transparency, not with the act of resale itself.

Common Licensing Myths

“All cheap keys are illegal.” No. Legitimate perpetual licences can be resold at prices below the Microsoft Store RRP. The issue is key type, not price alone. A retail key sold at £34 is a different proposition to a key sold at £5 with no stated type and no support.

“If it activates, it’s genuine.” No. KMS keys activate cleanly. MSDN keys activate cleanly. Both can be revoked or lapse later. Activation at point of purchase is not a validity test.

“OEM licences can always be moved.” No. OEM is motherboard-bound. Moving it to a new machine is not permitted under the licence terms, and in most cases Windows won’t let you regardless.

“Volume and retail keys are the same.” No. They use completely different activation systems with different rules, different transfer rights, and different failure modes. The key format looks identical. The underlying licence is not.

“A digital licence means you own the software permanently.” A digital licence reflects activation status. It doesn’t change the underlying licence type. A KMS-backed activation stored as a digital licence still lapses when the server does.