In technical jargon, a distinction is made between the small and the large pillar 3a. Anyone with an income subject to AHV contributions can pay into the small pillar 3a. Only self-employed persons who are not affiliated to a pension fund can pay into the large pillar 3a. This is to replace the missing 2nd pillar.
A maximum of CHF 6’826 per year can be paid into the small pillar 3a and a maximum of CHF 34’128 per year into the large pillar 3a (as of 2020). Persons who are not affiliated to a pension fund (self-employed persons or those who do not earn the BVG minimum wage) may pay a maximum of 20% of their income into the restricted form of the 3rd pillar (3a).