Licences Cal Licenses

What Are Microsoft CALs?

A Client Access License (CAL) is a license that grants a user or device the legal right to access Microsoft server software. Unlike the server license itself — which covers the server installation — CALs cover the users or devices connecting to that server. This two-part licensing model is the foundation of Microsoft's on-premises server licensing and applies to Windows Server, SQL Server, Exchange Server, SharePoint Server, and Remote Desktop Services.

Every user or device that directly or indirectly accesses Microsoft server software needs a CAL. Indirect access includes scenarios like an employee using a web application that queries a SQL Server database on the back end, or a point-of-sale terminal that authenticates against a Windows Server domain controller. Microsoft audits enforce CAL compliance, and under-licensing can lead to significant financial penalties.

Types of CALs

Windows Server CALs — Required for every user or device accessing a Windows Server. This includes basic network services like file sharing, printing, DHCP, DNS, and Active Directory authentication. Windows Server CALs are separate from the Windows Server operating system license and must be purchased for each user or device.

RDS CALs (Remote Desktop Services CALs) — An additional CAL required on top of the Windows Server CAL when users remotely access a Windows Server desktop or individual applications. RDS CALs come in User and Device variants and are mandatory for any Remote Desktop Session Host or Virtual Desktop Infrastructure deployment.

SQL Server CALs — Required when SQL Server is licensed under the Server + CAL model (typically Standard edition for smaller deployments). Each user or device accessing the SQL Server needs a SQL CAL. For larger workloads, SQL Server can alternatively be licensed under the Per Core model, which does not require CALs.

Exchange Server CALs — Required for each user or device accessing an on-premises Exchange Server. Exchange CALs come in Standard and Enterprise tiers: Standard CAL covers email, calendar, and shared mailbox access, while Enterprise CAL adds advanced features like unified messaging, in-place hold, and data loss prevention.

CAL Suites — Microsoft bundles Core CAL Suite and Enterprise CAL Suite for organisations that need CALs across multiple server products. The Core CAL Suite includes Windows Server CAL, Exchange Server Standard CAL, SharePoint Server Standard CAL, and Skype for Business Server Standard CAL. The Enterprise CAL Suite adds Exchange Enterprise CAL, SharePoint Enterprise CAL, Skype for Business Enterprise CAL, and advanced compliance features.

How to Choose the Right CAL

User CAL vs Device CAL — A User CAL licenses a specific user to access the server from any device (desktop, laptop, phone, tablet). This is ideal for mobile workforces and organisations where employees use multiple devices. A Device CAL licenses a specific device to be used by any number of users. This is more cost-effective for shift-worker scenarios, shared workstations, or environments like call centres where multiple employees share the same computer throughout the day.

Server + CAL vs Per Core — For SQL Server, organisations with fewer users accessing a database server may find the Server + CAL model more economical. For internet-facing or high-volume applications where the number of users is unknown or very large, the Per Core licensing model is the better choice. Windows Server always uses the Server + CAL model (the server license is core-based, but CALs are always required).

RDS CAL requirements — If users will access a full Windows desktop remotely (Remote Desktop Session Host) or individual applications published via RemoteApp, RDS CALs are mandatory in addition to Windows Server CALs. This applies regardless of the remote desktop protocol or thin client used.

Licensing Compliance

Microsoft CAL licensing is enforced through periodic audits, including the Microsoft Software Asset Management (SAM) review program. Common compliance gaps include: forgetting that external contractors and partners need CALs; overlooking indirect access scenarios (middleware, web servers querying a SQL back end); assuming device CALs for BYOD scenarios are sufficient when employees use personal devices to access corporate servers; and failing to track CAL assignments across virtualised environments.

Lizensa recommends maintaining a CAL inventory spreadsheet, conducting annual internal license reconciliations, and consulting Microsoft licensing specialists when planning new server deployments. Each CAL purchase from Lizensa includes full documentation suitable for audit trails.

Frequently Asked Questions