Once you’ve signed on as self-employed at the Hacienda, those opening business in Spain need to communicate to the TGSS (“Tesoreria General de la Seguridad Social”, which in the UK would be known as “National Insurance”) that you’ve become self-employed. They will then start taking your monthly social security contributions out of your account. You have around thirty days to do this after you’ve signed on at the Hacienda.
You’ll need to take yourself down to your local TGSS office to become autónomo in Spain (here are a list of “delegaciones” in Barcelona). This part is very simple – you’ll need a photocopy of your passport, your NIE number and a photocopy of all the pages of your Módelo 036 or 037. You’ll fill in a form which you’re given, and – hey presto – you can now start paying social security contributions. Maybe you won’t be as keen to start celebrating this one. You’ll also be asked to choose a “mutua” (health insurance company) who will pay your insurance if you get sick – I choose one which I was advised by the woman at the counter as being one of the largest.