MDCG 2021-24: Classification of medical devices, explained

Who this applies to

This guidance applies to manufacturers classifying medical devices under the MDR, as well as notified bodies and authorities checking those decisions. It covers class I, IIa, IIb, and III devices and walks through the Annex VIII definitions and rules with examples.

It does not classify IVDs, which use IVDR Annex VIII. It also does not decide whether a product is a medical device in the first place. Qualification comes first; classification follows once the medical-device status and intended purpose are clear.

Classification starts with intended purpose

Classification is a legal and technical conclusion, not a marketing choice. Use the intended purpose expressed in the label, instructions for use, clinical evaluation, and promotional materials, together with the device's design and how it achieves its action.

Record the characteristics that drive the rules: duration of use, invasiveness, whether the device is active, whether it is implantable, anatomical site, energy delivered or exchanged, substances administered or removed, biological effects, medicinal substances, software function, and the consequences of an incorrect output.

Apply all rules that could plausibly cover the device. If several rules or sub-rules lead to different classes, the strictest rule and sub-rule resulting in the highest class applies. For a system, procedure pack, or device with multiple intended purposes or modes, classify the relevant functions and parts before reaching the overall result.

Definitions change the outcome

Many classification mistakes happen before anyone reaches a numbered rule. Annex VIII definitions control the path:

“Continuous use” needs a real use-scenario analysis. Temporary interruption for cleaning, disinfection, maintenance, or replacement in an immediately continuing treatment may not reset duration. Conversely, products used repeatedly on separate patients are not automatically one continuous use. Document the intended clinical episode rather than selecting the definition that gives the lowest class.

Work through the rule families

Rules 1–4 cover non-invasive devices, rules 5–8 invasive devices, rules 9–13 active devices, and rules 14–22 special cases. The special rules cover areas such as medicinal substances, contraception, disinfection, animal or human tissues and cells, nanomaterials, substances introduced into the body, therapeutic decision software, and certain active therapeutic devices.

For every applied or rejected rule, quote the decisive wording and tie it to a device fact. A defensible classification memo should let a reviewer see why the device is invasive or non-invasive, active or non-active, short- or long-term, and why each relevant condition is or is not met.

Accessories are classified in their own right. Software that drives or influences a device generally takes the same class as that device; standalone software is classified on its own. The physical location of software — cloud, phone, hospital server, or inside the device — does not decide the class.

Rule 11 for medical device software

Rule 11 is based on what the information or action is used for and the potential consequence of an error:

Do not classify from the screen or algorithm in isolation. Define the medical decision, the patient's condition, the role of the output in the clinical workflow, who reviews it, the time available to intervene, and the plausible harm from an incorrect, delayed, or missing output. Human review does not automatically reduce the class; its effectiveness has to be credible in the intended use.

For a deeper software-focused walkthrough and examples, see How to Classify Software as a Medical Device Under the MDR?. This explainer covers the guidance as a whole; that article concentrates on the Rule 11 decision.

What Rev.1 changes

Rev.1, published in April 2026, updates and clarifies the guidance while keeping the MDR's classification framework intact. If your classification memo cites an older version, revisit the revised definitions, rule interpretations, and examples that are relevant to your device rather than assuming the original conclusion still stands.

The guidance is not law and does not replace Annex VIII. Where an example resembles your device, compare the facts and intended purpose rather than treating the example's class as a product list entry.

What this means for you, practically

1. Lock the intended purpose first. Reconcile the exact medical purpose, users, population, use environment, operating principle, and claims across controlled documents.
2. Write a classification facts sheet. Capture duration, invasiveness, activity, anatomical site, substances, energy, software decisions, and worst credible consequences before choosing rules.
3. Assess every plausible rule. Record why each applies or does not; then apply the strictest rule and sub-rule instead of stopping at the first convenient answer.
4. Analyse functions separately. For modular software or multifunction devices, define boundaries and dependencies, then show how the final device class follows.
5. Repeat the assessment under change control. Intended-purpose, algorithm, workflow, population, duration, material, anatomical site, or energy changes can alter the applicable rule and conformity route.

Read the official MDCG 2021-24 Rev.1 guidance.