Windows Server 2025 Datacenter core add-on Key
- Key delivered by email right after payment
- Download link and activation guide included
- Secure checkout · digital product, nothing shipped
A Windows Server 2025 Datacenter core add-on licence adds core licences to a server that already has a Windows Server 2025 Datacenter licence. Use it when the server has more physical cores than your existing licence covers. You choose how many cores to add at checkout. You get the key by email after payment, with download and activation instructions.
- Number of cores selectable at checkout
- For servers with more physical cores than the base licence covers
- Must match the version and edition of your base licence (2025 Datacenter)
- Keeps unlimited VM rights when every core is covered
- Digital delivery: nothing is shipped
What is a core add-on licence, and when do I need one?
A core add-on licence covers extra physical cores on a server that already meets the 16-core minimum. Microsoft's terms require every physical core to be licensed, so a server with 24 cores needs 24 core licences, not just the base 16.
An add-on doesn't create a new server licence; it extends the one you have. Use it with the same Windows Server version and edition as your base licence.
| Physical cores in server | Base licence | Add-on cores needed |
|---|---|---|
| 16 | 16 cores | 0 |
| 20 | 16 cores | 4 |
| 24 | 16 cores | 8 |
| 32 | 16 cores | 16 |
| 48 | 16 cores | 32 |
What do you need before buying a Windows Server 2025 Datacenter core add-on?
| Requirement | Details |
|---|---|
| Base licence | A Windows Server 2025 Datacenter licence covering at least 16 cores |
| Same edition | Use Datacenter add-ons with a Datacenter base licence; all cores on a server must be licensed for the same edition |
| Physical core count | The total number of cores across all processors in the server |
| CALs | Core licences don't include CALs; users and devices still need Windows Server 2025 CALs |
Hardware requirements are the same as for Windows Server 2025 itself; the add-on doesn't change them.
Windows Server 2025 follows Microsoft's Fixed Lifecycle Policy. Mainstream support runs until 13 November 2029, and extended support, with security updates, until 14 November 2034.
How do core add-ons affect virtual machine rights on Datacenter?
Datacenter's unlimited VM rights apply only once every physical core in the host is licensed. An add-on that closes the gap between your base licence and the real core count restores full coverage.
| Standard | Datacenter | |
|---|---|---|
| Virtual machines per licensed host | 2 | Unlimited |
| Hyper-V | Yes | Yes |
| Storage Spaces Direct | No | Yes |
| Software-defined networking (Network Controller) | No | Yes |
| Host Guardian Hyper-V support (shielded VMs) | No | Yes |
| Best for | Small offices, single servers, up to 2 VMs | Heavily virtualised hosts and clusters |
How do I use a Windows Server 2025 Datacenter core add-on licence?
Windows Server isn't activated per core. The server is activated once with its product key, and your core licences set how many cores you're licensed for. Keep the add-on key and order email with your licence records.
- Check the server's total physical cores in Task Manager (Performance → CPU) or with
Get-CimInstance Win32_Processorin PowerShell. - Confirm your base licence is Windows Server 2025 Datacenter and note how many cores it covers.
- Subtract the base licence from the total to find how many add-on cores you need.
- Follow the instructions in your order email, and file the add-on key with your base licence.
A common mistake we see is counting threads instead of cores. A 24-core processor with hyper-threading shows 48 logical processors, but needs only 24 core licences.
Frequently asked questions
Can I use a core add-on without a base licence?
No. An add-on extends an existing Windows Server 2025 Datacenter licence that already covers the 16-core minimum. On its own, it doesn't license a server. If you're starting from scratch, get a full Windows Server 2025 Datacenter licence first, then add cores as needed.
How many add-on cores should I choose?
Subtract the cores your current licence covers from the total physical cores in the server. For example, a 28-core server with a 16-core licence needs 12 more. Choose that number at checkout, or the next available option above it.
Can I mix Standard and Datacenter core licences on one server?
No. All cores in a server must be licensed with the same edition. To move from Standard to Datacenter, license every core with Datacenter; Windows Server can then be converted in place with DISM, without reinstalling.
Do I need more CALs when I add cores?
No. CALs are counted per user or device, not per core, so adding cores doesn't change how many you need. Every user or device accessing the server still needs a Windows Server 2025 CAL, unless one of Microsoft's exceptions applies.
See all Windows Server 2025 licences, or browse all Windows Server products.
