Income tax rates apply to any income from work, including contracted temporary work (including specifically "authorship works" which IT services generally fell under and which get 20% "normalized expenses", though if your actual costs are higher, you _can_ document expenses instead). Method of calculation is slightly different because of expenses and treatment of gross income, but rates are the same by law.

They are, however, not treated as employees (which have a lot of protections like minimum hourly wage, maximum working hours, maximum daily and weekly overtime hours, minimum number of paid vacation days, sick leave coverage at 60% of salary...). For freelancers, this does cause trouble with the pension fund employees not wanting to count your contributions toward your pension, but it depends heavily on who deals with processing your forms.

And to further clarify, as early as 2008 when I looked at it first, social insurance payments were required at the same rates employers and employees pay, with the main benefit being that if you already have other income (eg salary), your total social contributions should are capped at 5 times the average (eg if you've got a 3x the average salary, and a side gig getting you another 3x the average salary, you'd only be paying self-reported social insurance taxes on the extra 2x average salary).