The IAE heading (the epígrafe, the code for your activity in the business activity classification) takes up one box on Modelo 036 and decides three things nobody connects with it: whether your clients withhold tax from you or not, which expenses fit your activity without argument, and whether you can use certain regimes. It is chosen in five minutes and carried for years. This guide explains how the classification is organised and how to read it so as to get it right first time.
What the IAE is, and why you fill it in if you are exempt
The IAE, the Impuesto sobre Actividades Económicas or business activity tax, is a local tax whose rates were approved by Real Decreto Legislativo 1175/1990. Individuals are exempt from paying it, and so are companies whose net turnover does not reach one million euros. But the exemption is from paying, not from being classified: the heading is still the code the tax authorities use to identify what you do, and obligations that do affect you hang from it.
A self-employed individual (an autónomo) practically never pays IAE. Even so, their heading decides whether their invoices carry withholding, whether they can use the objective method and which activity appears on their census entry when they apply to join the ROI, the register of intra-EU operators, or reply to a request for information. Choosing "whichever looks similar" because it costs nothing anyway is the source of half of the census inconsistencies that later have to be put right.
The three sections
| Section | What it covers | Practical consequence |
|---|---|---|
| One | Business activities: industry, retail and wholesale, services, hospitality, construction | As a general rule, your invoices carry no withholding |
| Two | Professional activities: lawyers, architects, doctors, translators, consultants, IT people acting as professionals | Your invoices to businesses and other professionals carry withholding |
| Three | Artistic activities: film, theatre, music, shows | Their own regime, with withholding in most cases |
The line between section one and section two is the one that really decides. It is not drawn by what you do but by how you do it: section two covers the personal exercise of a profession, while section one covers the business organisation of resources to provide a service. The same work can fall on one side or the other depending on whether it is supplied in your own name and personally, or through a structure with staff and resources.
Withholding: the most visible effect
If your heading is in section two, your business and professional clients withhold income tax on account from your invoices, at the general percentage set by the IRPF Regulations, with a reduced rate during the first years of activity. If it is in section one, as a general rule there is no withholding.
| Section one (business) | Section two (professional) | |
|---|---|---|
| Withholding on an invoice to a business | No, as a general rule | Yes |
| Withholding on an invoice to a private individual | No | No |
| Obligation to file Modelo 130 | Yes, under direct assessment | No, if at least 70 % of the previous year's income carried withholding |
| Cash flow | You collect 100 % and pay later | You collect less each month and reach the annual return with the tax paid in advance |
One consequence follows that shows from the first quarter: a professional with business clients is usually released from Modelo 130 under the 70 % rule, while a business owner always files it. They are two different ways of paying the same tax in advance, and neither is better: they change when the money goes out.
How to read the classification
The structure is hierarchical and is best read from top to bottom: division, grouping, group and heading. Each level narrows things down further. In section two there are also groups covering whole professions and headings that detail them.
- Describe your activity in one sentence, without sales adjectives. Not "I help brands grow", but "I design and code websites to order".
- Identify the main verb: manufacture, sell, repair, advise, teach, transport, broker.
- Decide whether you do it as a professional or through a business organisation. That answer chooses the section.
- Search within that section for the group covering that family and, within it, the most specific heading. The generic "other activities" headings are the last resort, not the first.
The classic mistake is to choose by the end product. Someone who records a photography course and sells it online may be engaged in teaching, trade or IT services depending on how the business is set up. The answer comes from how it actually operates, and you need to be able to explain it if someone asks: the consistency between heading, website, invoices and expenses is what holds the whole thing up.
Several activities at once
Nothing stops you being registered under several headings, and it is often the right thing to do. Someone who runs training and also sells digital templates does two different things, and both should appear. What you need to be clear about is that each registration brings its own treatment.
| Combination | What to watch |
|---|---|
| One professional heading and one business heading | Some invoices carry withholding and others do not. The 70 % rule for Modelo 130 is measured on the professional activity |
| Two activities with different VAT regimes | If one is exempt and the other is not, the pro rata rule may come in, and then input VAT is no longer fully deductible |
| One activity that could use módulos and one that could not | The objective method has incompatibility rules that can drag in the whole activity |
Adding a heading is a simple census change on Modelo 036 (remember that the 037 has been abolished since 3 February 2025) and it is done before the new activity starts, not when the first invoice is issued.
The heading and VAT: two classifications that are not the same
A frequent confusion is worth clearing up: the IAE heading does not set the VAT rate or decide whether an activity is exempt. They are two different sets of rules, with two different logics. The applicable rate and the exemptions come from Ley 37/1992, the VAT Act, and from the nature of the transaction, not from the local tax's classification.
What does happen is that the two classifications have to be consistent with each other. A teaching heading with invoices charging VAT at the standard rate, or a retail heading with every invoice exempt, are combinations that catch the eye as soon as someone cross-checks the data. When the real activity has two components (for example, exempt training and taxable sales of materials) the sensible thing is for the census to show both and for VAT to be handled under the rule that fits each, including the pro rata rule if it comes into play.
The heading and deductible expenses
An expense is deductible when it is linked to the income of the activity, and that link is judged against what your census entry says you do. The same expense can be beyond question for one heading and debatable for another: the photographer's camera, the installer's tools, the subscription to a legal database. When the heading does not fit the real activity, every expense becomes a conversation.
That is the practical reason we insist on this so much. It is not about the theory of economic classification: it is about making sure that, on the day a request arrives, the code on your census entry and the invoices for your expenses tell the same story.
Four activities that are almost always misclassified
| Activity | Where people put it | What to ask yourself first |
|---|---|---|
| Software development to order | Depending on the case, under a business heading for IT services or under a professional one | Do you act as a professional in your own name, or have you organised resources and a team to supply the service? |
| Content creation and monetisation through platforms | Almost always under a generic heading that describes nothing | Is what you are paid for advertising, a licence of rights, production services, or several things at once? |
| Training | Under teaching, full stop | Do you deliver it yourself, in person, or do you sell a recorded product? The section changes and the VAT changes |
| Your own e-commerce | Under any retail heading | What exactly do you sell, and do you make it, buy it ready-made or act as an intermediary? |
In all four cases the right answer depends on facts that only the person setting up the business knows. That is why we do not give a table of "recommended heading by profession": it would be convenient and it would be false. What we give is the method, and the warning that a classification chosen for convenience is paid for later in every argument about expenses or withholding.
If the heading is wrong
It is corrected with a census declaration of change. What is worth looking at before filing it is what the change drags backwards: if the previous heading implied withholding and none was applied, or the other way round, there is a substantive side to sort out as well as the formal one. The consistency of your tax address also counts, and if it is out of date it is fixed on the same form, as we explain in when the tax census does not back you up.
Doing it on your own initiative always turns out better than waiting. The difference between putting things right before or after a request is set out in what counts as a prior request.
If you are about to register and are not sure which section you belong in, tell us in two lines what you are going to do through the self-employed registration form and we will look at it before you file anything. The full registration route is in registering step by step and the page for this area in registering as self-employed. We cannot guarantee that the tax authorities will share a particular classification; what we do is choose it on a sound basis and leave it supported in writing.