Engineering & Professional Services Firms: How to Calculate Your Payroll Costs (2026)

Managed payroll by headcount for an engineering firm

10 employees: $450 a month, $5,400 a year; 25 employees: $1,125 a month, $13,500 a year; 50 employees: $2,250 a month, $27,000 a year; 100 employees: $4,500 a month, $54,000 a year. Every row is $45 per employee per month, all-inclusive, inside the payroll software you already use, with no monthly minimum, so the per-employee cost is the same at 10 as at 100. Nothing in the engineering firm setup, prevailing wage for government projects, billable hour payroll allocation, PE license classification and field vs office payroll, is billed as an add-on.

The employer-side tax that rides on every engineering firm wage

At the May 2025 national median for civil engineers, $100,840 a year or about $48 an hour, the employer share of Social Security and Medicare is $7,714 per employee per year and FUTA is $42 after the state credit, before state unemployment at the assigned rate. Those costs are the same whoever runs payroll; the calculator question is only who does the work and who carries the error.

Employers use Form 8974 to determine the qualified small business payroll tax credit for increasing research activities that can be claimed on the employment tax return; related forms listed by the IRS include Forms 941, 943, 944 and 6765.

The in-house line in the calculation

BLS OEWS May 2025: payroll and timekeeping clerks, national median $58,260, mean $59,630. Add roughly 30 percent for benefits and employer taxes, about $75,738, before the software that person runs, and set it against the headcount rows above. Managed payroll stays under that loaded figure until about 140 employees.