Self-employed workers in Spain are commonly known as autonomos. Their registration process has to be made with the Spanish tax authority and the Social Security in Spain.
Most autonomos have to present quarterly IVA (VAT) returns and an annual income tax return (I.R.P.F.). Other declarations are frequently applicable on a quarterly and annual basis, according to circumstances.
Also, self-employed workers in Spain have to make social security contributions to the Spanish social security system through the Special Regime for Autonomous Workers (Régimen Especial de Trabajadores Autónomos or RETA). Most autonomos pay a flat rate Social Security, no matter how much or how little you earn. You have to make the payments even if you don’t earn anything one month, so make arrangements to cover payments if necessary.