Client Access Licenses in 2026: User vs Device CALs, RDS and SQL CALs, and What Microsoft 365 Already Covers

Windows Server is licensed on the server side by physical core: all cores, with minimums of 8 per processor and 16 per server. That license lets the software run; it does not let anyone connect. Every user or device that accesses a Windows Server for its standard services — file shares, print, authentication, an application that sits on it — needs a Client Access License, and that is true for Standard and Datacenter alike. Our Windows Server licensing calculator adds the CAL line to both editions for that reason.

Two properties of the Windows Server CAL cause most of the surprises. Nothing enforces it: there is no license server, no activation, no counter in Server Manager. And it is version-bound in one direction: a Windows Server 2025 CAL covers a 2025 server and every earlier release, while a 2019 or 2022 CAL does not cover a 2025 server.

The one model that removes the Windows Server CAL is pay-as-you-go through Azure Arc, introduced with Windows Server 2025: no CALs are required for standard functionality, and the operating system is billed monthly to your Azure subscription. RDS CALs are still required.

A User CAL covers a named person on any number of devices. A Device CAL covers a physical device for any number of people. Count the people who touch the server estate and count the devices that touch it; then compare.

• An office where every employee has a laptop and a phone: 120 people, 240 devices. User CALs.
• A warehouse with three shifts sharing thirty terminals: 90 people, 30 devices. Device CALs.
• Mixed estates are normal; each user or device simply has to be covered by one type or the other.

The rules on reassigning a CAL, or switching from one type to the other, live in the Microsoft Product Terms; check the current wording before you plan on moving CALs between joiners and leavers. For RDS CALs, Microsoft's licensing article gives 90 days as the minimum before a per-user CAL can be reassigned. The Client Access License Calculator takes users and devices as separate inputs and shows the cost of each route.

Remote Desktop Services is where CALs become visible, because they are enforced. Every user or device that connects to an RDS session host — or an Azure Virtual Desktop session host running Windows Server — needs an RDS CAL on top of the Windows Server CAL, issued by a Remote Desktop Licensing server. The mechanics, from Microsoft's RDS licensing article:

• Per-device RDS CALs are tracked. A device gets a temporary CAL on first sign-in, valid for 90 days, upgraded to a permanent CAL on the next connection if one is available.
• Per-user RDS CALs are not enforced. The license server keeps issuing from an overused pool; staying within your count is the administrator's job, and over-allocation is a breach of the license terms.
• There is a 120-day grace period before a license server is required. After it, clients without a valid CAL cannot sign in.
• Compatibility runs one way: a 2025 RDS CAL reaches 2025 and earlier session hosts, a 2022 RDS CAL cannot reach a 2025 host, and 2025 RDS CALs install only on a 2025 license server.

Two things are easy to get wrong. No Microsoft 365, Office 365 or Enterprise Mobility + Security plan includes RDS CALs; CAL equivalency, below, does not extend to them. And Azure Arc pay-as-you-go, which waives the Windows Server CAL, still requires RDS CALs. Azure Virtual Desktop on a Windows client operating system is licensed differently; check the AVD documentation before carrying the count across.

SQL Server has two licensing models. Per core licenses the instance by the cores it runs on and asks nothing about who connects. Server + CAL licenses the instance and then every user or device that accesses it, directly or through an application.

In 2026 Server + CAL is effectively a Standard edition choice: Microsoft's edition documentation for SQL Server 2025 notes that Enterprise edition under Server + CAL is not available for new agreements and, where it still exists, is capped at 20 cores per instance. Per core is the model for Enterprise, and for any Standard instance whose user population you cannot count.

That last clause is the decision rule. If every employee uses an application in front of the database, every employee needs a SQL CAL; a web or application tier in between does not reduce the count. Microsoft calls this multiplexing and defines it in the Product Terms. When the population is genuinely uncountable — a public website, a partner portal — per core is the compliant model by rule.

SQL CALs are not covered by any Microsoft 365 plan and are separate from the Windows Server CAL the same user already needs. Our SQL Server licensing calculator prices Server + CAL against per core.

Here is the layer that saves money when understood and creates audit findings when assumed. The Microsoft Product Terms contain a table of CAL Equivalency Licenses: online-service subscriptions that grant the licensed user the same access rights as specific on-premises CALs. A user covered by an equivalent subscription does not need a separate Windows Server CAL to reach your file server.

Microsoft 365, Office 365 and Enterprise Mobility + Security seats are the subscriptions that carry equivalency; our Exchange Server SE guidance treats Microsoft 365 E3 or E5 seats as covering the Exchange CAL for every user who touches an on-premises server. The Client Access License Calculator works from the same table: enter the cloud plans your users hold and it removes the CALs those seats already stand in for.

What we will not do is reproduce the table from memory. The mapping is by plan and by CAL, and it changes when Microsoft updates the Product Terms. Open the current CAL Equivalency Licenses section under Client Access Licenses and Management Licenses and read it against your own plan mix. The Business plans are the common trap: do not assume a Microsoft 365 Business Premium seat carries a Windows Server CAL right until you have seen it in the current table.

Three boundaries hold regardless: equivalency is per licensed user, so a shared kiosk with no licensed user still needs a Device CAL; it never covers RDS or SQL Server CALs; and it covers access, not the server license. With the plan mix known, the count is mechanical, and the calculator does the arithmetic.

Do I need CALs for Datacenter as well as Standard?

Yes. The edition changes virtualization rights, not access rights. The exception is Azure Arc pay-as-you-go, where no CALs are required for standard functionality.

Do my Microsoft 365 licenses replace RDS CALs?

No. Equivalency covers server CALs such as the Windows Server CAL; Microsoft's pay-as-you-go article states that RDS CALs are still required even when the Windows Server CAL is waived.

Can I buy 2025 CALs for a 2019 server?

Yes; a newer CAL covers earlier servers, so the next server build does not trigger a second purchase. The reverse is not true.

What happens if I run out of RDS CALs?

Per-device: a temporary CAL works for 90 days, then stops if no permanent CAL is available. Per-user: nothing stops, but you are out of compliance from the first extra user, and Microsoft puts the tracking on the administrator.

How do I confirm which plans carry equivalency?

Read the CAL Equivalency Licenses table in the current Product Terms, then enter the same plans into the CAL calculator. If the two disagree, tell us; the calculator is maintained against the table.

• Microsoft Learn: License Remote Desktop Services with Client Access Licenses (CALs)
• Microsoft Learn: Configure Windows Server Pay-as-you-go with Azure Arc
• Microsoft Learn: Editions and supported features of SQL Server 2025
• IT Partner: Windows Server 2016 End of Support on 12 January 2027; Exchange Server 2016 and 2019 Are Out of Support

The Product Terms were not reproduced; where a rule lives only there, the text says so.