Flexi-Job vs Student Worker vs Interim: Which Contract and What You Must Track

If you roster occasional staff in Belgium, you are probably choosing between three contracts: a flexi-job worker, a student worker, or an interim (agency) worker. They look similar on a shift plan, but they are legally distinct, and, crucially, each one is tracked differently. A flexi-job needs a Dimona with code FLX before work starts, either a day Dimona with start and end times for each shift or a period Dimona backed by approved electronic time registration; a student is tracked against a 650-hour annual contingent under a student Dimona code; an interim worker’s hours are split between the staffing agency and your own joint committee. Get the wrong record for the wrong worker and a single mixed-workforce audit can turn expensive fast. Suivo’s time tracking solution tags each worker by category and applies the right rule to each, so you are not depending on someone remembering three rulebooks at 6am. This guide explains the differences and what you must register for each.

What is the difference between the three worker types?

Flexi-job worker. Someone who already works at least 4/5 of a full-time job with another employer during the reference quarter (the third quarter before the flexi-job starts, “Q-3”), or who is legally retired. Since 1 July 2026, flexi-jobs are open to almost all sectors, subject to your joint committee not opting out. The appeal is the favourable social treatment: a 28% employer contribution, 0% worker contribution, and flexi-income that is tax-free up to EUR 18,440 for income year 2026 for non-retired workers (unlimited for the legally retired).

Student worker. A student working under a student employment contract, benefiting from reduced solidarity contributions instead of full social security, as long as they stay within an annual contingent of favourable hours. The social security portal tracks that contingent through the student Dimona code.

Interim (agency) worker. A temporary worker supplied by a staffing agency. The agency is the legal employer, handles the Dimona and payroll, and the worker’s activity is governed both by the agency’s joint committee (PC 322) and by the joint committee of your business where the work is done.

How is each worker type tracked?

This is where the three diverge, and where mistakes happen. The table below summarises the core tracking obligation for each.

	Flexi-job	Student worker	Interim (agency)
Legal employer	You	You	The staffing agency
Dimona code	FLX: a day Dimona (DimDay) with start and end times per shift, or a period Dimona of at most one quarter	STU (student code), booking hours against the contingent	Filed by the agency (interim code)
Key limit to watch	Wage cap and the EUR 18,440 tax-free threshold	650-hour annual contingent of favourable hours	Agency contract terms and PC 322 rules
Time registration	Start and end times registered electronically since 1 July 2026 (a day Dimona with times counts; a period Dimona needs an approved system)	Working-hours record required; contingent must not be exceeded	Hours recorded for the agency; you still need presence proof on site
Who files the declaration	You, before work starts	You	The agency
What an inspector checks	DimDay timestamp vs hours worked	Hours booked against the contingent	Match between agency declaration and actual presence

A few points that catch employers out:

• The Dimona has no grace period. For a flexi-job, the Dimona must be filed before the worker starts and cannot be done retroactively. Miss it and the work can be requalified as ordinary employment, with ordinary social security contributions and loss of the flexi tax advantage, and a missing Dimona is a level 4 offence under the Social Penal Code, fined per worker.
• The 650-hour contingent is annual and shared. A student’s favourable hours are counted across all their employers for the year, not just yours. Go over the contingent and full contributions apply. You can check remaining hours before you roster.
• Interim does not remove your obligations. The agency files the Dimona, but you still need to prove the worker was present on your site and worked the hours invoiced. Presence registration protects you if the agency’s records and reality diverge.

Which contract should you use?

There is no single right answer, but the trade-offs are clear:

• Choose a flexi-job when you have recurring, flexible demand and access to people who already hold a main job or are retired. The social cost is low and the worker keeps more of the wage, but eligibility is strict and the DimDay discipline is unforgiving.
• Choose a student worker for seasonal peaks and lighter roles, watching the 650-hour contingent. The reduced contributions are attractive, but only within the limit.
• Choose interim when you need to fill a gap fast without becoming the legal employer, accepting the agency margin in exchange for the agency handling declarations and payroll.

Many operations use all three at once, which is exactly why classification errors are the most expensive mistake in a mixed-workforce audit: apply a flexi-job rule to a student, or forget an interim worker was on site, and the retroactive assessment lands on you.

How does a connected platform reduce the risk?

The problem is not knowing the rules once; it is applying the right rule to the right person on every shift, every day. A scheduling solution that distinguishes worker categories applies a DimDay check to flexi-jobs, contingent tracking to students, and presence proof to interim workers automatically, so the rule follows the worker instead of living in someone’s head. Feeding those verified hours into Suivo’s workforce management platform gives you one record across all three categories, payroll-ready and defensible in an audit.

For the full flexi-job rules, see our complete employer guide to flexi-jobs in Belgium. To manage all three worker types together on one roster, read our guide to managing a mixed workforce.

Frequently asked questions

What is the difference between a flexi-job and a student job in Belgium?

A flexi-job worker already works at least 4/5 elsewhere in the reference quarter or is legally retired, and is declared with Dimona code FLX before work starts. A student works under a student employment contract with reduced solidarity contributions, within an annual contingent of 650 favourable hours, declared with code STU.

How many hours can a student work in Belgium with reduced contributions?

A student can work 650 hours a year with reduced solidarity contributions. The contingent is counted across all the student’s employers for the year, not just yours. If the student goes over it, full contributions apply, so check the remaining hours before you put them on the roster.

Who files the Dimona for an interim worker?

The staffing agency does. The agency is the legal employer and handles the Dimona and payroll. You still need to prove that the worker was present on your site and worked the hours invoiced, which protects you if the agency’s records and reality differ.

When should you choose a flexi-job, a student or an interim worker?

Choose a flexi-job for recurring, flexible demand when you can reach people with a main job or who are retired. Choose a student for seasonal peaks and lighter roles within the 650-hour contingent. Choose interim to fill a gap fast without becoming the legal employer, in exchange for the agency margin.

What does a social inspector check for each type of worker?

For a flexi-job worker, the inspector checks the Dimona against the registered start and end times. For a student, they check the hours booked against the contingent. For an interim worker, they check that the agency’s declaration matches the worker’s actual presence on your site.

Track every worker type by the right rule

Suivo tags each worker by category and applies the correct tracking rule to each: DimDay for flexi-jobs, contingent for students, presence for interim. One connected platform, one record, ready for any inspection.

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