The more common forms (modelos) that need to be filed for a freelancer are:
Form 030 is filled by private individuals liable for tax payment to request the assignment of a tax identification number (NIF) when engaging in tax-related transactions.
Form 036: Registration of a freelancer or company before the tax office. This indicates to the tax office that thge person or company will be engaged in professional activities or pay wages subject to withholding.
Form 037: This is a simplified version of the Form 036 for those who fulfill certain requirements. This form is usually suitable for freelancers.
Form 100: The annual income tax form for individuals. See our personal taxes page for more information.
Form 130: Quarterly estimated tax payments for individuals.