The 38-hour working week is one of Belgium's best-known labour-law principles, yet its practical application regularly trips up HR managers and business owners. Averaging arrangements, reference periods, and the specific rules for part-time workers add layers of complexity that are easy to mishandle. Here is a clear, practical overview.
The 38-hour norm: an average, not a fixed weekly ceiling
Belgian law sets the standard working week at 38 hours, but this does not mean every employee must work exactly 38 hours in every calendar week. The law allows employers to average hours over a reference period, as long as certain thresholds are respected:
- The daily limit is normally 8 hours (or 9 hours under a five-day week arrangement).
- The weekly limit can reach 40 hours without those extra hours formally counting as overtime, provided the average across the reference period stays at 38 hours.
- The internal limit caps how many hours above the weekly average an employee can accumulate during the entire reference period before a correction is required.
These thresholds interact directly with overtime rules. For a deeper look, our article on Belgian overtime rules, daily limits and the internal cap covers the mechanics in detail.
Reference periods: choosing the right timeframe
The default reference period under Belgian law is one quarter, or 13 weeks. Sector-level or company-level collective agreements can extend this to a maximum of one year. A longer period offers more scheduling flexibility to absorb busy seasons and quieter spells, but it also demands more rigorous tracking to avoid unpleasant surprises at the closing date.
A few practical points to keep in mind:
- The work rules (arbeidsreglement/règlement de travail) must explicitly state the chosen reference period and the averaging formula.
- At the end of each reference period, any hours accumulated above the average must be settled: either as compensatory rest or as paid overtime.
- Sector-specific deviations exist in construction, hospitality, security and transport, among others, and can differ substantially from the general framework.
A reliable digital system tracks each employee's running hour balance against their reference period and flags when the internal limit is approaching. Tikkit does this automatically, so you are never caught out at the end of a quarter.
Part-time workers: same logic, different baseline
Part-time employees follow the same averaging logic, but their reference point is their contractual hours rather than 38 hours. An employee on a 24-hour contract cannot routinely work 30 or 32 hours without those additional hours being classified as complementary hours, which carry their own obligations.
Complementary hours for part-time workers are a particularly sensitive area:
- They must be recorded accurately and compensated in line with applicable rules.
- Beyond a certain threshold, they can trigger a contractual modification or attract a wage supplement.
- The permitted margins are defined in the employment contract and the work rules.
Accurate working-time registration matters at least as much for part-time staff as it does for full-time employees. Deviations from the contracted schedule accumulate quickly, and reconstructing the history without reliable timestamped data is difficult when questions arise during an inspection.
Building good habits ahead of the 2027 mandate
From 2027 onwards, working-time registration will be mandatory for virtually all Belgian employers. If you already use an averaging arrangement, now is a sensible time to make sure your recording practices are solid. Spreadsheets and paper logs rarely hold up when a labour inspector asks for a detailed breakdown by employee, by day, and by reference period. Our overview of what Belgian labour inspectors actually look for shows exactly what needs to be in order.
Tikkit provides a structured solution: employees clock in and out via the mobile app, a kiosk or a QR code, and the platform continuously monitors legal thresholds per reference period for each individual. The result is a clean, auditable record that reflects your averaging arrangement accurately.
The 38-hour working week is not a rigid constraint. It is a flexible framework, designed to give employers and employees room to adapt, provided the rules are followed consistently. The key is knowing those rules, embedding them in your work rules, and tracking compliance every day, for every member of your team.
This article is general information, not legal advice. Always verify your situation with your social secretariat or a legal adviser.