Do I have to pay Turkish social security as a freelancer?

If you register as self-employed or as a sole trader in Turkey, membership of the 4/b scheme — commonly called Bağ-Kur — is compulsory, and the premium is due monthly regardless of whether you invoiced that month. The premiums are deductible from your tax base. If you are employed by a foreign employer with no presence in Turkey, the position depends on whether a social security agreement between Turkey and that country applies to you.