Build the annual requirement
Add the gross owner-compensation target, business overhead and a planning buffer. Keep personal income tax separate unless the model explicitly handles it.
Estimate billable capacity
Multiply working weeks by hours per week, then by the fraction that can genuinely be billed. Admin, sales, leave and internal work reduce that fraction.
Test the workload
Compare several realistic billable fractions and working-week assumptions. The result supports planning; it is not a promise of take-home income.