ADV days (ADV dagen or adv-dagen, from arbeidsduurvermindering: reduced working time) are rest days that compensate for a weekly schedule that is longer than the agreed average working week. Since 2003, weekly working time in Belgium must be reduced to 38 hours, which can be met as an average. So a team that works 40 hours a week can get 12 rest days a year to bring the average down to 38. That is the example from FOD WASO (Federal Public Service Employment), not a national entitlement. The real number depends on your paritair comité (joint committee), your company agreements and the schedule people actually work.
Suivo’s time tracking software keeps hours, absences and rest days in one record for payroll. Below: how ADV works, who decides the number, and how to record it correctly.
What are ADV days?
The Arbeidswet (Labour Act of 16 March 1971) caps working time at 8 hours a day or 40 hours a week. According to FOD WASO, since 1 January 2003 every company must have reduced weekly working time to 38 hours (law of 10 August 2001). That does not have to mean an actual 38-hour week.
Companies can meet the 38-hour rule in two ways:
- An actual 38-hour week, respected every week. For example, a working day of 7 hours 36 minutes.
- An average of 38 hours over a reference period. Employees keep working a longer schedule, for example 5 days of 8 hours, and get extra rest days to compensate. Those rest days are the ADV days.
Companies that did not apply a 38-hour week on 1 January 2003 were moved by law to an actual 38-hour week.
ADV suits construction well, where crews work full days and the company prefers whole days off over shorter days. A crane operator who stops 24 minutes earlier every day gains little. A full rest day is easier to plan on a site and usually more valuable to the worker.
Why do some sectors have 12 ADV days (and others none)?
The number is arithmetic. Take the hours your schedule runs above the agreed average, multiply them by the weeks worked, and divide by the length of a working day.
| Schedule | Agreed average | Extra hours per week | Extra hours per year (about 48 weeks) | ADV days |
|---|---|---|---|---|
| 40 hours (5 x 8) | 38 hours | 2 | 96 | 12 (8-hour days) |
| 38 hours (5 x 7h36) | 37 hours | 1 | 48 | about 6 (7h36 days) |
| 38 hours (5 x 7h36) | 38 hours | 0 | 0 | 0 |
The 48 weeks is a simplification: it leaves out about four weeks of statutory holidays. Your sector or company may count the reference period differently.
FOD WASO gives two worked examples:
- A 40-hour schedule brought to an average of 38 hours with 12 rest days a year.
- A sector with a 38-hour week brought to a 37-hour yearly average in a company with 6 extra rest days a year.
That is why the answer to “why 12 ADV days?” is simply: 40 hours worked, 38 hours agreed. Sectors or companies that reduce the working day itself (for example 7h36 a day) have no ADV days, because there is nothing to compensate. Others combine both. FOD WASO mentions a 37h30 week plus 3 rest days, which gives a 37-hour average.
According to SD Worx, some sectors rule out ADV and others add formalities before you can introduce it. So always check your joint committee first.
What about construction (PC 124)?
According to FOD WASO, companies under the joint committee for construction (PC 124) have 6 rest days a year fixed by Royal Decree as working time reduction, on top of 6 rest days a year fixed by sector CAO. The FOD WASO PC 124 fiche gives the yearly working time as 38 hours, with a normal week of 40 hours over the first five days. This applies to construction workers (arbeiders) in PC 124. It does not apply to white-collar staff or to other joint committees. One of the sector CAOs cited in the fiche ends on 31 December 2026. The sector has already published 12 collective rest days for 2027, so check the 2027 calendar for your region.
Ready-mix concrete companies within PC 124 follow a different model. Their average weekly working time over the year from 1 April to 31 March may not exceed 40 hours, and the daily working time can be set at 10 hours. That is an averaging rule for the whole year, not a fixed number of ADV days. See our construction industry page for how Suivo supports site crews and drivers.
Who decides the number: law, sector CAO or company?
The law sets the frame (the 38-hour average). The number of ADV days is set lower down. According to FOD WASO, working time reduction is usually set by:
- A sector CAO (collective labour agreement) of your joint committee, whether or not it is made generally binding by Royal Decree.
- A company CAO.
- The arbeidsreglement (work regulations).
- The individual employment contract.
Limits set by a sector or company CAO replace the legal limits (Arbeidswet, art. 28).
Pay. A reduction through a CAO made generally binding by Royal Decree must not lower pay: hourly wages are adjusted. The legal reduction to 38 hours must not lead to a pay cut either. Pay is not legally protected in the same way when the reduction comes from a non-binding sector CAO, a company CAO, the work regulations or the contract. Check the wording of your own agreement.
For a company with a mixed workforce, this is where it gets complicated. Blue-collar and white-collar staff often fall under different joint committees, with different ADV rules, in the same company. Our guide on time registration for a mixed workforce shows how to apply the right rule to each group.
How are ADV days planned: collective or individual?
There are two basic models, and many companies mix them:
- Collective days: the whole company, or a whole sector, is off on fixed dates. Easy to plan around.
- Individual days: each employee chooses when to take their days, within the rules. More flexible, but harder to plan on sites and routes.
FOD WASO advises that the agreement should set both how the rest days are fixed and how they are allocated when employees join or leave during the year. Work schedules must be in the work regulations, and for flexible schedules the work regulations or CAO must state the average weekly working time and the hours to work over the reference period.
According to SD Worx, ADV days are compensatory rest days, so in principle the employee takes them in the same year they are built up, depending on the sector rules. Put the rules on timing in your CAO or work regulations to avoid disputes.
For transport teams: when you plan driver routes and orders with scheduling software, treat collective ADV days as days with no drivers available, and plan individual days as early as you can.
How do you record ADV days correctly in time registration?
No official source sets a specific legal format for recording ADV days. The rules are in your CAO or work regulations, and your time registration system should track the days. In practice, a clean setup looks like this:
- One ADV rule per group. Link each employee to their joint committee and schedule, so the system knows the agreed average and the number of days.
- Show build-up and balance. Employees and HR see how many days are earned, taken and left.
- Record an ADV day as its own absence type, not as holiday, sickness or “other”. Payroll needs the separate code.
- Keep the worked hours as registered. Hours above the ADV average are not automatically overtime. In FOD WASO’s examples the weekly limit used for overtime pay and compensatory rest stays at 40 hours (or 38 hours).
- Handle joiners and leavers exactly as your agreement says.
- Load collective days in advance, so nobody is planned on a site or route that day.
- Export the ADV code to your social secretariat with the rest of the month’s hours. See our guide on connecting time registration to your social secretariat.
This matters more from 2027. The government plans a general obligation to register working time from 1 January 2027, with a transition period to 31 March 2027. As of September 2026 it is still a draft law, but as reported by SD Worx, the draft asks for a record of the time actually worked, not hours copied from a roster. An ADV day is a day not worked, so it must be clearly separated from worked days in that record.
How do ADV days differ from holidays, overtime recovery and compensatory rest?
| ADV days | Statutory holidays | Overtime recovery | |
|---|---|---|---|
| Why you get them | Your schedule is longer than the agreed average | Legal annual leave | You worked beyond the working-time limits |
| Set by | Sector CAO, company CAO, work regulations or contract | Law | Law and your CAO |
| Built up | By working the longer schedule | In the year before (according to SD Worx, unlike ADV) | When the limit is exceeded |
| Record as | ADV absence code | Holiday code | Recovery code, linked to the overtime |
Sickness and other absences are a separate topic. Our article on absence management in Belgium covers what to record from day one.
Frequently asked questions
Why do some employees get 12 ADV days?
Because they work 40 hours a week while the agreed average is 38. Two extra hours a week over roughly 48 working weeks makes 96 hours, or 12 days of 8 hours. FOD WASO uses this 40-to-38-hour example with 12 rest days, but your own number depends on your sector and company rules.
What are ADV days?
ADV days (arbeidsduurvermindering, reduced working time) are rest days granted because the weekly schedule is longer than the agreed average working week. Over the reference period, the rest days bring the average back down to the agreed level.
What are the rules for ADV days?
The legal framework is the Arbeidswet and the 38-hour average that applies since 2003. The number of days, how they are planned and whether they are paid are set by your sector CAO, company CAO, work regulations or employment contract.
How many ADV days do you get from age 45?
FOD WASO’s explanation of working time reduction does not link ADV days to age. If extra days depend on age in your company, that comes from a sector or company agreement, so check your joint committee’s CAO and your work regulations.
Get ADV right for every group
ADV is simple arithmetic until you have construction workers, drivers and office staff under different agreements in one company. One record that knows each person’s rule, shows the balance and sends the right code to payroll saves hours at every month end. Start with the group that causes the most corrections today.
