RDS CAL Explained: User or Device, License Server, Versions

Published October 23, 2026 · Updated October 23, 2026

Every user and device that connects to a Remote Desktop session host running Windows Server needs an RDS CAL (Remote Desktop Services client access license). It comes in addition to the Windows Server CAL, is bought per user or per device and is issued by a license server. Without a license server, a session host runs for 120 days; after that it rejects connections without a valid RDS CAL. This article explains the two models, the license server, the version rule and what applies to used RDS CALs.

Contents

• What an RDS CAL is and when you need one
• User CAL or device CAL for RDS
• The license server: role, activation, grace period
• Which RDS CAL matches which server
• What works without an RDS CAL
• Azure Virtual Desktop and service providers
• Buying used RDS CALs
• Frequently asked questions

What an RDS CAL is and when you need one

Microsoft states the rule in one sentence: each user and device that connects to a Remote Desktop Services session host or an Azure Virtual Desktop session host running Windows Server needs an RDS CAL. This is the classic terminal server on which users open a graphical session with a desktop or applications.

The RDS CAL does not replace the Windows Server CAL; it comes on top. The license terms for Windows Server 2025 require, in addition to a Windows Server CAL, the corresponding version of the Remote Desktop Services CAL for each user or device that directly or indirectly uses Remote Desktop Services or uses the server software to host a graphical user interface. Microsoft calls this an additive CAL: it must be licensed in addition to the base CAL. How to count the base CALs is explained in Windows Server CAL: user or device CAL.

For the products themselves, the Product Terms for Windows Server 2025 list three access licenses: the Windows Server 2025 CAL, the Windows Server 2025 Remote Desktop Services CAL (device and user) and the Windows Server 2025 Remote Desktop Services External Connector.

User CAL or device CAL for RDS

There are two types of RDS CALs: per device and per user. Which one you need depends on how your users or devices access the session host. Microsoft gives a clear rule of thumb: the per device model fits where two or more shifts of workers use the same computers; the per user model fits where each user has their own dedicated Windows devices.

The difference in enforcement is the most important point in practice. With user CALs, the license server issues a license to every user without checking the stock. Microsoft says so explicitly: it is the administrator's responsibility to ensure that all users have valid licenses. If you own 60 user CALs and 80 users sign in, you get no error message, but you are out of compliance. A list of users against your stock is therefore mandatory, also for preparing for a license audit.

The license server: role, activation, grace period

RDS CALs are not entered on the session host but on a Remote Desktop license server. It installs, issues and tracks the CALs; the session host requests them from there. The prerequisite is a Windows Server with the Remote Desktop Licensing role service. The license server must run at least the Windows Server version of the CALs it manages: RDS CALs for Windows Server 2022 can be installed on a license server running 2022 or later, but RDS CALs for 2025 cannot be installed on a license server running 2022.

The process in three steps:

1. Install the role: set up the Remote Desktop Licensing role service, including the licensing tools, on a Windows Server.
2. Activate the license server: in Remote Desktop Licensing Manager, automatically over the internet (outbound over TCP port 443 to the Microsoft Clearinghouse), through a web browser or by telephone.
3. Install the CALs: also in Licensing Manager, with the license code or agreement number from your purchase.

Until that is in place, the grace period helps: for 120 days a session host needs no license server. Once the grace period ends, clients must have a valid RDS CAL issued by a license server, or they can no longer sign in to a remote session. A license server can issue CALs across domains and forests and in workgroups, but in a workgroup only device CALs are possible, because per user tracking is not supported there.

Which RDS CAL matches which server

The same version rule applies to RDS CALs as to Windows Server CALs: later CALs work with earlier session hosts, earlier CALs do not work with later ones. Microsoft's example: with RDS CALs for Windows Server 2022 you can connect to session hosts running 2022 or earlier, but not to a session host running 2025.

For planning this means: if you run a terminal server on Windows Server 2019 today and plan 2025 as the next version, you need RDS CALs of version 2025; the old 2019 CALs remain valid for the old host. The server license itself is separate; the core rules are in Windows Server 2025 licensing.

What works without an RDS CAL

Two concurrent remote connections for administration are allowed without an RDS CAL; that is the Remote Desktop for administrators that every Windows Server includes. For more than two administrative connections or for user sessions, the Remote Desktop Session Host role service and RDS CALs are required.

Windows Server Essentials is not a terminal server: according to the licensing guidance, only the RD Gateway role service is supported, not the other RDS role services, including the session host.

For external users there is the RDS External Connector. Additive External Connector licenses must, like additive CALs, be assigned in addition to the base license. For your own workforce, RDS CALs remain the way to go.

Azure Virtual Desktop and service providers

For Azure Virtual Desktop, the license depends on the operating system of the session host. If the session host runs Windows Server, Microsoft requires an RDS CAL with Software Assurance (per user or per device) or an RDS User Subscription License. If it runs Windows 10 or 11 Enterprise, a per user license such as Microsoft 365 E3, E5, Business Premium, Windows Enterprise E3 or E5 or Windows VDA per user is enough. Per user access pricing for external users is not available for Windows Server session hosts.

Service providers that offer Remote Desktop as a service license it under the Services Provider License Agreement (SPLA) with RDS Subscriber Access Licenses for all unique users per month, not by concurrent sessions.

Buying used RDS CALs

RDS CALs from volume licensing agreements are perpetual licenses and may be resold in the EU. The legal basis is the exhaustion principle in Article 4(2) of Directive 2009/24/EC, confirmed by the Court of Justice of the European Union in case C-128/11: after the first sale in the Union with the rights holder's consent, the rights holder can no longer oppose the resale, not even with contractual bans; the previous owner must make their copy unusable.

Three things count when you buy: the version (it must match the session host, see the table), the model (user or device, by the rule of thumb above) and the documents: proof of first sale in the European Economic Area (EEA), the previous owner's declaration and an unbroken chain of ownership. You then install the license like any other RDS CAL through Licensing Manager. The legal background is explained in Is used software legal?

Frequently asked questions

What is an RDS CAL?

The access license for the Remote Desktop Services of Windows Server. Every user or device that opens a session on a session host needs one, in addition to the Windows Server CAL.

Do I need an RDS CAL in addition to the Windows Server CAL?

Yes. The Windows Server CAL covers access to the server's services, the RDS CAL covers Remote Desktop Services. Microsoft lists the RDS CAL as an additive CAL that comes on top of the base CAL.

How do I activate RDS CALs?

You do not activate the CALs but the license server: install the Remote Desktop Licensing role service, activate it in Licensing Manager (automatically over port 443, through a browser or by telephone), then install the CALs with the license code or agreement number.

How long does a terminal server run without a license server?

120 days. After that, clients must have a valid RDS CAL from the license server, or signing in to the remote session fails.

Does an RDS CAL 2022 work with a Server 2025?

No. Earlier RDS CALs do not work with later session hosts. An RDS CAL 2025, on the other hand, works with session hosts running 2025, 2022, 2019 and 2016.

Why do I get no warning with user CALs when licenses are missing?

Because the per user model is not enforced. The license server issues a license to every user, and the administrator is responsible for having enough licenses.

Do I need RDS CALs for Azure Virtual Desktop?

For session hosts running Windows Server, yes, with Software Assurance or as a subscription license. For session hosts running Windows 10 or 11 Enterprise, a per user license such as Microsoft 365 E3 or Windows Enterprise E3 is enough.

What Lizenzus does for you

We supply used RDS CALs as user and device CALs with the three documents for every license. The available versions are listed under RDS CAL, the matching base licenses under Windows Server CALs. In your quote request, tell us the version of your session host, the number of users or devices and whether you work in a domain or a workgroup. Your quote request is non-binding.

Sources

• Microsoft Learn: License your RDS deployment with client access licenses, accessed October 23, 2026
• Microsoft Learn: Activate the Remote Desktop Services license server, accessed October 23, 2026
• Microsoft Learn: Install RDS client access licenses, accessed October 23, 2026
• Microsoft Learn: Remote Desktop licensing across domains, forests and workgroups, accessed October 23, 2026
• Microsoft Learn: Troubleshoot Remote Desktop disconnected errors, accessed October 23, 2026
• Microsoft Learn: Remote Desktop Services roles, accessed October 23, 2026
• Microsoft Learn: Azure Virtual Desktop licensing, accessed October 23, 2026
• Microsoft Licensing: Windows Server 2025 licensing guidance, accessed October 23, 2026
• Microsoft Licensing: Product Terms, Windows Server Standard, Datacenter and Essentials, accessed October 23, 2026
• Microsoft: Microsoft License Terms, Windows Server 2025 Datacenter and Standard, section 4, accessed October 23, 2026
• Official Journal of the EU: Directive 2009/24/EC, Article 4(2)
• Court of Justice of the EU, judgment of July 3, 2012, C-128/11 UsedSoft, paragraphs 70 and 77