What is the basic formula?
Day rate = (yearly income you need + social contributions + tax + business costs + pension savings) ÷ billable days.
Each term has to be yours: there is no standard rate for a developer, an architect or a project manager in Belgium, and averages mix very different profiles. What a day rate must absorb, and why it is not a salary, is covered in our definition of the day rate. This page is about the calculation.
How many days can you actually invoice?
Start from the calendar. A year has about 261 weekdays, and Belgium has 10 public holidays, as the SPF Employment lists, so around 251 working days remain in a year when no holiday falls on a weekend. Then deduct, with your own assumptions:
- The holidays you plan to take
- Sick days, which are not paid for incapacities of seven days or less
- Training and certification days
- Days spent on sales, admin and accounting
- Gaps between two assignments, often the least predictable item
A rate built on 251 billable days assumes you never stop. Build it on a conservative figure, and treat any extra day as a margin.
What costs go into the rate?
Social contributions first: in 2026, 20.5% of net professional income up to €75,024.54, then 14.16% up to €110,562.42, plus your fund’s management fees, according to INASTI. The mechanism is in what social contributions a freelancer pays.
Then income tax or, through a company, corporate tax and your director’s pay. Then business costs: accountant, professional liability insurance, hardware, software licences, training, travel. Finally, what an employer would otherwise fund: pension, income protection, and holidays. VAT is not part of the rate: a day rate is quoted excluding VAT.
How do you check the rate before quoting it?
Compare it with three things. The rate a client or agency is prepared to pay for your profile in your sector. Your current net income as an employee, converted with the method in freelancer or employee: which pays more. And the billing model: a time and materials assignment pays per day worked, while a fixed-price assignment shifts the risk of overruns to you.
If you work through an agency, the rate you negotiate is the one in your own contract, as explained in how freelancing through an agency works. Then look at the current contract and permanent roles to see which profiles are in demand.
