The CNMC Speed Test: What It Measures and What It Does Not Prove

The National Commission on Markets and Competition (CNMC) provides an online tool for checking an internet connection. Its website describes it as an official, free speed test, and it covers fibre, Wi-Fi and 4G/5G mobile networks. It is an accessible starting point for anyone experiencing slow speeds and looking for a reference measurement. It is not an automatic certification that the service you pay for does—or does not—meet its terms. CNMC speed test.

That distinction matters because the figure shown at the end depends on the entire connection at that particular moment: the device, the link between it and the router or mobile network, the route to the test server, and any activity sharing the connection. A low result therefore indicates reduced performance during that test, but does not identify the cause on its own. To help investigate, repeat the measurement under comparable conditions and make a note of how you carried it out.

A speed test is generally useful for examining data-transfer performance at a particular time. Download speed matters when receiving content, while upload speed matters when sending files or streaming video. But a high figure does not necessarily mean that every task will feel fast. Latency describes how long communication takes to respond; it can matter for video calls, online games and other interactions that are sensitive to delay. The CNMC has specifically explained that speed and latency are different aspects of the connection experience. CNMC: “It’s not the speed, it’s the latency”.

Check which measurements appear on the results screen and which units they use, rather than attributing metrics to the tool that have not been confirmed in its current documentation. The material consulted confirms that the test exists, but does not provide enough detail here to establish its complete methodology, server locations or the calculation of each indicator. This limitation is a reason to treat the result as an indication, not as a comprehensive technical audit. Latency alone cannot explain every problem with an application, either: the device, remote service or network route may also play a part.

When you test over Wi-Fi, the test measures the performance reaching your device through the home wireless network, not just the connection supplied by your provider. Distance from the router, obstacles, the band in use and nearby networks can all have an effect. A wireless result below the nominal fibre speed does not, by itself, prove that there is a fault on the line. To distinguish the possibilities more effectively, when practical, compare a computer connected to the router by Ethernet cable with a Wi-Fi test taken in the same place where you normally use the connection.

On a mobile phone, the situation is different: the test uses the cellular network available in that location at that time. Coverage, cell load and the device can affect the result; moreover, a 4G measurement should not be presented as equivalent to a 5G test. The CNMC tool explicitly identifies fibre, Wi-Fi and 4G/5G as test scenarios. CNMC speed test. Record the access type alongside each result so that you do not compare measurements taken under different conditions.

A single run may coincide with a background download or a momentary change in performance. For a more representative reference, repeat the test several times, spacing out the measurements and avoiding simultaneous changes to the device, location or connection type. Close downloads and streams that are not necessary; if other people are using the network, make a note of it. There is no need to turn this into a complicated experiment: the essential point is to associate each result with observable conditions.

Before contacting your provider, save the date and time, device, whether you were connected by cable or Wi-Fi, your approximate location in the home, and screenshots of the results. Compare the measurements with the speed and terms in your contract, without assuming that one figure is conclusive proof. In Spain, the charter of rights for users of electronic communications is set out in Royal Decree 899/2009. For a specific complaint, check the current rules and applicable procedure, because a screenshot of a test does not replace those requirements. Royal Decree 899/2009, BOE.

A short checklist for documenting the problem:

• Date and time of each test.
• Connection used: cable, Wi-Fi or mobile data.
• Device and place from which you measured.
• Relevant network activity and repeated results.

The test can help answer a limited question: what performance that connection recorded in those tests and under those conditions. If the problem recurs over cable and at different times, you will have a more consistent indication to describe to your provider than if you have only one isolated wireless measurement. Even so, identifying the source may require checks of the router, device or provider’s network that the test does not carry out on its own.

A good one-off figure does not rule out brief outages, fluctuations at other times or problems specific to an application. Nor does a poor Wi-Fi result automatically prove that the provider is delivering less than the contracted service. The CNMC also offers frequently asked questions about the tool; consult that documentation for up-to-date instructions, especially if you need to know exactly what data it stores or how each mode works. Speed test FAQs. The prudent conclusion is simple: measure, record the context, repeat and compare. Use the result as indicative evidence to investigate, not as a definitive diagnosis or a guarantee of resolution.