Remote Desktop Services (RDS) CALs Explained: What They Are, When You Need Them, and User vs Device
An RDS CAL is the license a user or device needs to connect to an RD Session Host, and the RDS CAL user vs device choice decides whether you license each person or each device that connects. Either type is in addition to the regular Windows Server CAL, not a replacement for it.
Remote Desktop Services (RDS) lets people run a full Windows desktop or individual apps on a central server instead of on their own PC. It’s a popular way for small businesses to give remote staff access to accounting software, line-of-business apps, or a shared desktop.
RDS has its own licensing layer, though, and it’s separate from the regular Windows Server CAL. This guide explains what an RDS CAL is, when you need one, how per-user and per-device RDS CALs differ, and the version rules that trip people up.
What is an RDS CAL?
An RDS CAL (Remote Desktop Services Client Access License) is the license a user or device needs to connect to an RD Session Host, the Windows Server role that hosts remote desktops and apps.
Microsoft’s documentation says each user and device that connects to a Remote Desktop Services session host needs an RDS CAL. You install RDS CALs on a Remote Desktop license server, which issues and tracks them. When someone connects, the session host checks with the license server, and the license server issues an RDS CAL if an appropriate one is available.
RDS CALs are in addition to Windows Server CALs
This is the most common misunderstanding. An RDS CAL doesn’t replace the regular Windows Server CAL.
Microsoft classes the Windows Server CAL as a Base CAL and the RDS CAL as an Additive CAL. Its licensing guide says additive CALs must be licensed in addition to the corresponding base CALs.
So every person or device using RDS needs:
A Windows Server CAL (user or device), and- An RDS CAL (user or device).
If you haven’t sorted out base CALs yet, start with our guide to Windows Server User CALs vs Device CALs.
When do you need RDS CALs?
You need RDS CALs when users or devices connect to an RD Session Host to run a remote desktop or remote apps. Typical small-business examples:
- Staff working from home sign in to a shared server desktop to use accounting or ERP software.
- A branch office runs a line-of-business app hosted on the main office server through RemoteApp.
- Thin clients or shared terminals connect to a session host instead of running apps locally.
Microsoft’s Product Terms go a step further. They say the RDS CAL is also required for using Windows Server to host a graphical user interface, whether through Remote Desktop Services functionality or other technology. In other words, third-party remote-app or desktop-hosting tools running on Windows Server don’t remove the RDS CAL requirement.
When you don’t need RDS CALs: remote administration
IT staff connecting to a server to manage it are the main exception. Microsoft’s documentation says Remote Desktop supports two concurrent remote connections for administration without RDS CALs.
To allow more than two administrative connections, or to let regular users connect, you need to install the RD Session Host role and have the appropriate RDS CALs.
Per-user vs per-device RDS CALs
Like base CALs, RDS CALs come in two types. When you set up licensing, you choose the deployment’s Remote Desktop licensing mode: Per User or Per Device. Microsoft’s own examples are a good guide:
- Per device suits environments where two or more shifts of workers use the same computers.
- Per user suits environments where each user has their own dedicated device(s).
The technical differences matter more than most guides admit. Here’s how Microsoft describes them:
| Per-device RDS CAL | Per-user RDS CAL | |
|---|---|---|
| Assigned to | Each device | A user in Active Directory |
| Works in a workgroup (no domain) | Yes | No |
| Enforced by the license server | Yes, can’t be over-allocated | No. It can be over-allocated, which breaches the license terms |
| Temporary licenses | Issued on a device’s first sign-in, valid 90 days | Not available |
| Revoking | Up to 20% can be revoked | Can’t be revoked |
| Renewal / reassignment | Renews every 52–89 days (random) | Shows 60 days before renewal; 90 days before it can be reassigned to another user |
What that means in practice
- No domain? Use per-device. Microsoft says if your RDS servers are in a workgroup, you have to use Per Device CALs. Per User CALs aren’t permitted in that setup.
- Per-user is on the honor system. With per-user licensing, Microsoft says licensing isn’t enforced. The license server will keep issuing licenses even after you run out, and it’s the administrator’s responsibility to make sure every user has a valid license. You can use the Remote Desktop Licensing Manager to track and report per-user RDS CALs.
- Per-device is enforced. The license server won’t over-allocate per-device RDS CALs. If you replace PCs, you can revoke up to 20% of per-device RDS CALs.
Worked examples
Example 1: Remote office staff. 10 employees each have a company laptop and sometimes connect from home PCs. Each needs to reach the session host from more than one device. The domain is set up with Active Directory. Answer: 10 per-user RDS CALs, plus base Windows Server CALs for the same 10 users.
Example 2: Shift workers on thin clients. 4 thin clients at a front desk are used by 12 staff across three shifts. Nobody connects from elsewhere. Answer: 4 per-device RDS CALs, plus 4 base Windows Server Device CALs.
Example 3: A small workgroup server. A 5-person office runs one server with no domain, and staff connect from their own desktops. Answer: per-device RDS CALs, because per-user isn’t permitted in a workgroup. That’s 5 per-device RDS CALs (one per desktop), plus base CALs.
Version rules: match RDS CALs to your session host
Microsoft is strict about RDS CAL versions. Older RDS CALs can’t connect to a newer session host, but newer RDS CALs can connect to older ones.
| Session host runs | 2025 RDS CAL | 2022 RDS CAL | 2019 RDS CAL | 2016 RDS CAL |
|---|---|---|---|---|
| Windows Server 2025 | Yes | No | No | No |
| Windows Server 2022 | Yes | Yes | No | No |
| Windows Server 2019 | Yes | Yes | Yes | No |
| Windows Server 2016 | Yes | Yes | Yes | Yes |
The license server has its own rule: you can install RDS CALs only on a license server running the same Windows Server version as the CALs, or later. For example, Windows Server 2025 RDS CALs need a license server running Windows Server 2025.
A simple way to stay safe: run your license server on your newest Windows Server version, and buy RDS CALs that match your newest session host.
The 120-day grace period
Microsoft gives a 120-day licensing grace period during which no license server is required. After that, clients must have a valid RDS CAL issued by a license server before they can sign in to a remote session.
Treat the grace period as setup time, not a trial. Plan to have your license server activated and your RDS CALs installed well before it ends.
External users
If people outside your organization, such as clients or contractors who aren’t onsite, use your RDS server, Microsoft allows two options: RDS CALs for each external user or device, or an RDS External Connector license for each physical server they access. Like the RDS CAL, the RDS External Connector is additive: Microsoft says it must be assigned in addition to the base access license, meaning Windows Server CALs or a Windows Server External Connector.
Choosing your RDS CALs
Windows Server 2022 session host: Windows Server 2022 Remote Desktop 5 User CALs, alongside base CALs such as the Windows Server 2022 5 User CAL pack.- Windows Server 2019 session host: Windows Server 2019 Remote Desktop 5 User CALs (2022 RDS CALs also work on a 2019 host).
- Windows Server 2025 session host: you’ll need 2025 RDS CALs, plus Windows Server 2025 User CALs as your base CALs. For 2025 RDS CALs, or for per-device RDS CALs, request a quote and we’ll help.
You can browse server licenses, CALs, and RDS CALs on our Windows Server licenses page.
If you’re also choosing a Windows Server 2025 edition for your session host, our Windows Server 2025 Standard vs Datacenter guide compares the two.
Frequently asked questions
An RDS CAL is a Remote Desktop Services Client Access License. Microsoft requires one for each user or device that connects to a Remote Desktop session host running Windows Server, in addition to the regular Windows Server CAL.
Yes. Microsoft treats the Windows Server CAL as a base license and the RDS CAL as an additive license. Anyone using Remote Desktop Services needs both.
Choose per-user when each person has their own device or connects from several devices. Choose per-device when several people share the same computers, such as shift workers. If your servers are in a workgroup rather than a domain, Microsoft requires per-device RDS CALs.
Not for basic administration. Microsoft says Remote Desktop supports two concurrent remote connections for administration without RDS CALs. More than two administrative connections, or any regular user connections, need the RD Session Host role and RDS CALs.
No. RDS CALs only work with session hosts running the same or an earlier version of Windows Server. A Windows Server 2025 session host needs Windows Server 2025 RDS CALs.
Microsoft provides a 120-day grace period during which no license server is required. After it ends, users or devices must get a valid RDS CAL from an activated license server before they can sign in to a remote session.
Yes. RDS CALs are installed on a Remote Desktop license server, which issues and tracks them. The license server must run the same version of Windows Server as the RDS CALs, or a later one.
Get your Remote Desktop licensing right
Tell us your session host version, how many people connect, and whether you use a domain or a workgroup. We’ll help you match RDS CALs and base CALs to your setup.
- Business or volume orders: request a quote.
- Questions about an order: email support@solveditservices.com (fastest), or call (447) 223-5297.
- More answers are on our FAQ page.