Register for IAE (choose your epígrafe and declare it at Hacienda)

What you need

1. Cl@ve, certificado digital or DNIe working. Without this you can't do the online steps.
2. Be clear on what you will do to choose the correct Epígrafe IAE. The IAE tariffs are a sudoku: pick the one that best describes your real activity.
3. Start date nailed down. The registration must go before you start or, at most, within the first month if you need the 840.
4. If you're a sociedad, have the escritura and the NIF provisional ready.

Documentation

1. DNI/NIE (autónomo) or NIF de la sociedad + escritura if applicable.
2. Certificado digital/Cl@ve to sign on sede.agenciatributaria.gob.es.
3. Epígrafe IAE (and secondary ones if you do several activities).
4. Address and referencia catastral of the local or rental contract if you'll work from premises.
5. Municipio where you'll be taxed for IAE (where you carry out the activity).
6. IBAN to domiciliate the municipal bill if you're not exempt.
7. Turnover last year if you approach or exceed 1.000.000 €.

Step by step

1. Go to sede.agenciatributaria.gob.es with Cl@ve/certificado and open Censo de empresarios (Modelo 036/037).
2. Fill the alta indicating the actividad and the exact Epígrafe IAE, municipality and start date. If there's a local, add it.
3. Sign and submit. Download the justificante of the 036/037: it shows your Epígrafe IAE.
4. If you're a sociedad, check in Mis expedientes that the 036 is filed (even if PAE/notaría claimed to have done it). If not, file it yourself.
5. If you're not exempt (e.g., you exceed 1.000.000 € or fall into non-exempt cases), file Modelo 840 (IAE) at the same sede within the first month from starting. This registers you in the municipal matrícula del IAE.
6. When the ayuntamiento has you in the padrón, domiciliate the IAE bill at their sede or when you get the payment notice. The payment is not made on the 840.
7. Keep all justificantes; you'll need them for licences, banks or Seguridad Social.

Expert tips

1. Epígrafe first, licences after: the epígrafe must match your activity/licence. If it doesn't, you'll get bounced around.
2. Don't invent dates: late census registration = possible sanción (típicamente 200€). Better to file on time, even if you haven't invoiced yet.
3. Multiple epígrafes: include all that apply. It avoids corrections and headaches with withholdings/IVA.
4. Don't confuse IAE with a licence: IAE is with AEAT and the bill is municipal; the licence is a separate ayuntamiento procedure.
5. If one year you exceed 1.000.000 €, review things: you may have to pay IAE the following year and submit extra information to Hacienda.

Common mistakes

1. Not declaring the epígrafe because “I'm exempt”. Mistake: exemption is for payment, not for declaring.
2. Picking a catch-all epígrafe that doesn't fit. Later it conflicts with licences or VAT rules.
3. Forgetting the 840 when required. Result: municipal surcharges and ‘padrón de oficio’ letters.
4. Filing the 036/037 late. Fine and awkward if they ask for justificantes.
5. Paying in the wrong place: the 840 is not a payment; the bill comes from the ayuntamiento. Set up direct debit and forget about it.