New Expat salary Calculations

Does anyone here know how the new expat salary is applied in real terms. Does the 30% tax benefit apply to the gross salary or taxable amount (i.e. after social security & other such deductions).

I have seen confusing info online

"https://www.sd.be/loonsimulator/public/?lang=EN"

Thanks for the link calculator does not take into consideration, the expat status