This article explains the common mistake of many freelancers not to quote when they should.

http://gestionpyme.com/la-polemica-jubilacion-de-los-trabajadores-autonomos/

This article explains how the calculation to determine the retirement pension is:

http://www.consumer.es/web/es/economia_domestica/finanzas/2004/09/29/109571.php?page=2

This article talks about the financing of the pension:

http://financialred.com/como-calcular-nuestra-pension/

Website to calculate the pension:

http://www.ibermutuamur.es/spip.php?page=formulario-cuota-autonomo