To work a flexi-job in Belgium, a person must clear one of two eligibility routes. Either they were already employed at least 4/5 of a full-time job with one or more other employers during the reference quarter, known as Q-3, or they are legally retired. The 4/5 rule is the test most employers get wrong, because it looks at a quarter in the past, not the worker’s situation today. Getting eligibility right matters: if a worker turns out not to qualify, the flexi-job classification collapses and full social security contributions fall due. Alongside eligibility, since 1 July 2026 every employer engaging a flexi-job worker must have electronic time registration in place. Suivo’s workforce management platform provides that record and supports the same-day Dimona checks that keep each shift compliant. This guide explains who qualifies and how it is verified.
What is the 4/5 rule for flexi-jobs?
The 4/5 rule is the core eligibility test for non-retired flexi-job workers. To qualify, a person must have been employed at least four-fifths (4/5) of a full-time schedule with one or more employers other than the one now offering the flexi-job, measured during the reference quarter.
The logic is deliberate. A flexi-job is meant to be extra work on top of a substantial main job, not a way to replace regular employment with a lower-cost contract. Requiring a 4/5 main occupation ensures the worker already has full social security cover from their primary employer, which is why the flexi-job itself carries a 0% worker contribution and a 28% employer contribution.
Two details decide most cases:
- The 4/5 employment must be with a different employer (or employers) than the one offering the flexi-job.
- It is measured over the reference quarter, not the week you want to hire. That is the point people miss.
What is the Q-3 reference quarter?
Eligibility is not judged on the worker’s situation today. It is judged on the third quarter before the flexi-job begins, which is why it is called Q-3.
Belgium divides the year into four calendar quarters (Q1 January to March, Q2 April to June, Q3 July to September, Q4 October to December). Q-3 means you count back three quarters from the quarter in which the flexi-job starts. For example:
- A flexi-job starting in Q3 2026 (July to September) is assessed against Q4 2025 (October to December).
- A flexi-job starting in Q1 2026 (January to March) is assessed against Q2 2025 (April to June).
So the question is never “does this person work 4/5 right now?” It is “was this person employed at least 4/5 of full-time with another employer during the reference quarter three quarters ago?” Someone who started a full-time job last month does not yet qualify, because the reference quarter predates their current employment. This lag is the most common source of eligibility errors.
Who qualifies without the 4/5 test?
Legally retired workers take a different route. If a worker has reached legal retirement and draws a pension, they qualify for a flexi-job without the 4/5 employment test. They also benefit from a more generous income rule: while non-retired workers keep flexi-income tax-free only up to EUR 18,440 for tax year 2026 (indexed), legally retired workers can earn unlimited flexi-income.
That makes retirees a valuable and low-friction pool for flexi-job hiring: no reference-quarter calculation, no annual tax ceiling to monitor. For sectors with steady flexible demand, the retiree route is often the simplest path to a compliant flexi-job.
How is flexi-job eligibility verified?
Eligibility is not something you confirm once and forget. It is checked at declaration time and can be reviewed in an inspection.
- At the Dimona stage. When you file the flexi-job Dimona, Belgian social security systems can flag whether the worker meets the conditions based on their employment history in the reference quarter. The social security portal holds the employment data that underpins the 4/5 assessment.
- Through the framework agreement. A written framework agreement (raamovereenkomst) must be signed between you and the worker before the first shift. It is the document that formalises the flexi-job relationship.
- During a social inspection. SIOD inspectors can review whether the workers you engaged actually qualified, alongside DimDay timestamps and hours records. If a worker did not meet the 4/5 rule and was not retired, the flexi-job status fails and full social security contributions apply retroactively.
Because eligibility depends on history you do not control, the safe practice is to confirm status before the first shift rather than assume it. A worker who left their main job, or dropped below 4/5 in the relevant quarter, may not qualify even though they seem like an obvious fit.
What else must be in place before day one?
Passing the eligibility test is necessary but not sufficient. Before a flexi-job worker starts, you also need:
- A signed framework agreement, in writing, before the first employment.
- A confirmed joint committee position. Since 1 July 2026 flexi-jobs are open to almost all sectors, but sectors can opt out on a quarterly basis during the transition, so confirm your paritair comite with the FPS Employment has not opted out.
- A same-day Dimona (DimDay) filed before every shift, with no grace period.
- Electronic time registration, now mandatory for flexi-jobs and heading toward mandatory for all employers from 1 January 2027.
For the complete set of 2026 rules, see our complete employer guide to flexi-jobs in Belgium. To see how the flexi-job compares with student and interim contracts, read flexi-job vs student worker vs interim.
Check eligibility, then track it right
Suivo helps Belgian employers keep flexi-jobs compliant from day one: DimDay support, electronic time registration, and one connected record ready for any NSSO or SIOD inspection.
