Article 51 of the MDR, Regulation (EU) 2017/745, divides devices into classes I, IIa, IIb and III, using the 22 rules in Annex VIII. MDCG 2019-11 Rev.1, the MDCG guidance on software, was revised in June 2025. MDCG 2021-24 Rev.1 covers the classification rules in general.
Most classification mistakes do not come from picking the wrong rule. They come from not checking all the rules that apply. This article explains how Annex VIII is built, the definitions it relies on, the implementing rules, the 22 rules by group, and how they apply to software. For a comparison with the US system, see our article on classification of medical devices in the EU and US.
The four classes
Article 51(1) sets four classes: I, IIa, IIb and III. Within class I, Article 52(7) gives separate conformity assessment routes for devices:
placed on the market in sterile condition (often called "Is");
with a measuring function ("Im");
that are reusable surgical instruments ("Ir").
These are not extra classes. They are class I devices for which a notified body is involved in specific aspects.
The class determines the conformity assessment route under Article 52, the level of notified body involvement, the clinical evidence expected and the PSUR frequency. Our article on EU MDR requirements maps those obligations.
Start with the intended purpose
Implementing rule 3.1 says the application of the classification rules is governed by the intended purpose of the device. The classification is based on what the manufacturer claims, not every possible use.
In our view, this is where most weak classifications start. An intended purpose that describes the technology but not the clinical use leaves the rule selection open to challenge. It should say what the device is for, who uses it, on which patients and what decisions it supports.
The definitions that drive the rules
Chapter I of Annex VIII defines the terms the rules depend on. The most important are about duration:
| Term | Meaning |
|---|---|
| Transient | Normally intended for continuous use for less than 60 minutes |
| Short term | Normally intended for continuous use for between 60 minutes and 30 days |
| Long term | Normally intended for continuous use for more than 30 days |
Source: MDR Annex VIII, Chapter I.
Implementing rule 3.6 explains how continuous use is calculated, including temporary interruptions and immediate replacement by a device of the same type. Annex VIII also defines terms such as body orifice, surgically invasive device, reusable surgical instrument, central circulatory system and central nervous system. Article 2 defines invasive, implantable and active devices.
The implementing rules
Chapter II of Annex VIII sets the implementing rules. The ones used most often:
3.1: classification is governed by the intended purpose.
3.2: if a device is intended to be used with another device, the rules apply separately to each. Accessories are classified in their own right.
3.3: software that drives or influences the use of a device falls in the same class as that device. Software that is independent of any other device is classified in its own right.
3.5: if several rules, or several sub-rules within one rule, apply, the strictest rule and sub-rule resulting in the higher class apply.
Rule 3.5 is the one most often missed. You do not stop at the first rule that fits.
The 22 rules by group
| Group | Rules | Subject |
|---|---|---|
| Non-invasive devices | 1 to 4 | General non-invasive devices; channelling or storing blood, body liquids, tissues, liquids or gases; modifying the composition of blood or body liquids; contact with injured skin or mucous membrane |
| Invasive devices | 5 to 8 | Invasive via body orifices; surgically invasive transient; surgically invasive short term; implantable and long-term surgically invasive |
| Active devices | 9 to 13 | Active therapeutic devices; active devices for diagnosis and monitoring; software (Rule 11); active devices administering or removing medicinal products or other substances; all other active devices |
| Special rules | 14 to 22 | Including devices incorporating a medicinal substance (14), contraception (15), disinfecting devices (16), devices using non-viable tissues or cells (18), nanomaterials (19), substances absorbed by the body (21) and closed-loop systems (22) |
Sources: MDR Annex VIII, Chapter III; MDCG 2021-24 Rev.1.
Each rule has its own conditions and exceptions, so the group only tells you where to look. A single device can fall under rules from more than one group.
Rule 11 and software
Software is an active device under Article 2(4). Rule 11 classifies it by the information it provides and what it monitors:
software that provides information used to take decisions with diagnostic or therapeutic purposes is class IIa;
class III if those decisions may cause death or an irreversible deterioration of a person's state of health;
class IIb if they may cause a serious deterioration of a person's state of health or a surgical intervention;
software intended to monitor physiological processes is class IIa, or class IIb if it monitors vital physiological parameters whose variations could result in immediate danger to the patient;
all other software is class I.
Rule 11 is not the only rule for software. According to MDCG 2019-11 Rev.1, Rules 9, 10, 11, 12, 13, 15 and 22 should be considered for medical device software, and the strictest applies under implementing rule 3.5. The guidance also says software should be classified the same way regardless of its location or how it connects to hardware.
MDCG 2019-11 Rev.1 gives an example: melanoma image analysis software intended to be used with a near-infrared laser light scanner. The scanner is class IIa under Rule 10. The software drives the scanner, so implementing rule 3.3 applies, but Rule 11 also applies because of its diagnostic purpose. Under implementing rule 3.5, the software is class III.
Software that is an in vitro diagnostic medical device is classified under the IVDR, not these rules. Our article on medical device classifications for software and AI covers software in more depth.
A hypothetical example
Hypothetical example: a Dutch start-up develops software that analyses CT images and flags suspected findings for a radiologist.
Intended purpose: it writes down what the radiologist is expected to do with the flags, and for which patients.
Rule 11: the output supports diagnostic decisions, so the software is at least class IIa. The class rises if an incorrect flag could lead to serious or irreversible harm.
Implementing rule 3.3: it checks whether the software drives or influences the scanner. Only receiving images does not make it a driver.
Other rules: it checks Rules 9, 10, 12, 13, 15 and 22, as MDCG 2019-11 Rev.1 suggests, and applies the strictest result under implementing rule 3.5.
Documentation: it records the class and the reasoning in the technical documentation, as Annex II Section 1.1 requires.
If the intended purpose later changes, for example from flagging to triaging, the classification must be reassessed. Our article on SaMD technical documentation shows where the rationale belongs.
When the notified body disagrees
Under Article 51(2), a dispute between the manufacturer and the notified body about the application of Annex VIII is referred for a decision to the competent authority of the Member State where the manufacturer has its registered place of business. If the manufacturer has no registered place of business in the EU and has not yet designated an authorised representative, the matter goes to the competent authority of the Member State where the authorised representative referred to in Annex IX Section 2.2 has its registered place of business.
In our view, most disputes can be avoided by sending the notified body a clear classification rationale early, with every applicable rule addressed.
Conclusion
Annex VIII is a system, not a lookup table. The intended purpose decides which rules apply, the definitions decide how they apply, and implementing rule 3.5 decides which one wins. For software, Rule 11 is the starting point but not the only rule.
In our view, a good classification rationale lists every rule considered, explains why each does or does not apply, and is revisited whenever the intended purpose changes.
If you need help classifying your device under the MDR, our regulatory strategy team can help, or contact MedQAIR.
Frequently asked questions
How many classification rules does the MDR have?
22, in Chapter III of Annex VIII, grouped into non-invasive devices, invasive devices, active devices and special rules.
Is all medical device software at least class IIa?
No. Under Rule 11, software that does not provide information for diagnostic or therapeutic decisions and does not monitor physiological processes is class I, unless another rule gives a higher class.
What if more than one rule applies?
Implementing rule 3.5 applies the strictest rule and sub-rule, resulting in the higher class.
Does cloud hosting change the class of software?
No. According to MDCG 2019-11 Rev.1, software should be classified the same way regardless of its location.
Who decides when the notified body disagrees with the classification?
The competent authority of the Member State where the manufacturer has its registered place of business, under Article 51(2).
