This comparison almost always breaks at the same point: an employee's gross salary gets put next to an agency's invoice. Those are two different kinds of number, and the comparison therefore falls in the employee's favour every time.
What an employee really costs
Beyond gross salary: employer contributions, holiday pay and year-end bonus, insurance, a workplace, hardware and licences, training, and the time of whoever manages them. Add non-productive time, because leave, illness, meetings and admin appear in no agency rate.
And the cost that never makes it into a table: if this person leaves, their knowledge leaves too and you start again. At an agency that is the agency's problem.
What an agency person-year costs
That part is public. From the annual accounts Belgian agencies file with the National Bank themselves, calculated in IKAg's Agency Barometer: in financial year 2024 the median agency made about 76,000 euro of gross margin per full-time equivalent, the bottom quartile about 61,000. That is what an agency takes in as fees per person per year, after passing through costs such as media and production.
That figure is not a price you pay, but it is the best public benchmark that exists for what a person-year of agency capacity yields. If you buy half an agency FTE, you are in that range.
Where the balance tips
- Towards in-house as soon as the work returns every week, needs few switches of craft and a lot of product knowledge. You pay the learning curve once.
- Towards an agency as soon as the work peaks, needs several crafts at once, or is so specialised that you could never keep someone busy.
The third number nobody counts
Switching on and off. Hiring takes months and parting ways costs money and energy; an agency contract carries a notice period of three to six months. That flexibility is part of what you buy from an agency, and in the year your budget halves it is the most valuable part.
See also: what an advertising agency costs in Belgium and how many marketing people you need.