Part-time work: rules and pitfalls for employers

You want someone to work two days a week. Sounds simple. Draw up a contract, agree on the hours, done. But then the first question pops up: is that employee actually allowed to work only eight hours a week? And do you need to include all those work schedules in your work rules? And what if she stays a little longer than agreed one day: does that count as overtime?

Part-time work is bound by strict rules in Belgium. Rules with good intentions (protecting employees, social security), but ones you can easily trip over as an employer. In this article, we explain the key part-time contract rules, from the minimum working hours to the deviation register. Without legal jargon where it isn't needed, and with concrete examples where possible.

What makes a contract "part-time"?

Let's start with the basics. A part-time employment contract is any contract where the employee works fewer hours than a full-time colleague in the same category within your company. Do your full-timers work 38 hours a week? Then any agreement below those 38 hours is part-time.

Two things you need to get right from the start:

• The agreement must be in writing. That isn't always mandatory for full-time work, but for part-time work it is. No written contract? Then the employee can choose whichever work schedule suits them best. You don't want that.
• The contract must state the agreed working hours and the work schedule. For a fixed schedule: the exact days and hours. For a variable schedule: the average number of hours per week and the framework within which the schedules can vary.

The contract must be signed no later than the moment the employee starts working. Not the day after, not "next week". On day one.

Read more about the different types of employment contracts in Belgium in our detailed guide.

Minimum working hours: the one-third rule

Here's the key point. The weekly working hours of a part-time employee may not fall below one-third of the full-time working hours in your company. With a 38-hour week, that minimum is 12 hours and 40 minutes per week.

On top of that, there's a second minimum: each individual work period must last at least 3 hours. So you can't schedule someone for an hour and a half on a Tuesday afternoon. At least three hours per shift, no exceptions (unless a sector-level CLA states otherwise).

Important: change from 1 April 2026. The current one-third rule will be relaxed into a one-tenth rule. This means the minimum weekly working hours will drop to one-tenth of the full-time working hours. With 38 hours full-time, that becomes 3 hours and 48 minutes per week. The minimum of 3 hours per work period does remain in place.

When can you deviate from the one-third rule (until April 2026)?

Exceptions exist. A royal decree or a sector-level CLA can allow you to go below the one-third minimum. Think of:

• Cleaning staff in educational institutions
• Certain roles in the hospitality sector (JC 302)
• Employees with specific tasks that are shorter by nature

Always check the rules of your Joint Committee. What's allowed in one sector is a violation in another.

Work schedules: fixed or variable (and why it matters)

This is where it gets a bit administrative. Not boring-administrative, but exactly the kind of detail the social inspectorate looks at.

Fixed work schedule

With a fixed schedule, your employee knows exactly when they work. The same days, the same hours, every week. Easy, predictable.

But watch out: if that part-time schedule doesn't fully fit within the full-time schedules already listed in your work rules, you have to include the part-time schedule separately in your work rules. Employers often forget this. And it's precisely where an inspection can come unstuck.

A copy of the part-time employment contract (or an extract of it) must be kept in the place where the work rules are also available. That way, an inspector can immediately check whether the agreed schedule matches reality.

Variable work schedule

With a variable schedule, you alternate the working days and hours. Flexible for you as an employer, but with more obligations.

Your work rules must contain a general framework setting out:

• The average number of hours per week
• The limits within which the schedule can vary (earliest start, latest end, which days)
• The way you announce the schedule to the employee
• The notice period within which you must communicate the schedule (at least 5 working days in advance, unless your sector sets a different period)

You must keep the notice with the applicable work schedule for as long as it's in force, and for a full year afterwards. In paper or electronic form, it doesn't matter, but it has to exist.

At Recruit, we see this is one of the points where employers trip up most often. You think: I'll just send a WhatsApp with the schedule. But without a formal announcement following the rules in your work rules, you're in breach. A payroll partner like Recruit can automate this process, so your schedules are correctly registered and stored without you having to chase after it.

The deviation register: what it is and when you need it

Picture this: your part-time employee normally works from 9 a.m. to 2 p.m., but on a busy day you ask her to stay until 4 p.m. Those two extra hours have to be recorded somewhere. That's the deviation register.

The deviation register documents all deviations from the normal or agreed work schedules of part-time employees. It covers:

• Starting later than planned
• Stopping earlier or working longer
• Working on a different day than agreed

Who has to keep it? Every employer with part-time employees on the payroll.

Good news: if you have an electronic time-tracking system (think of a badge system or digital time registration), you don't need to keep a separate paper register. The electronic system is enough, provided it contains the same data: the employee's identity, the date, and the start and end time of the deviation.

After more than 15 years in Belgian payroll, we know the deviation register is one of those documents employers only think about when the inspectorate comes knocking. By then it's too late. A good time-registration system prevents that problem entirely.

We previously wrote an article about the cost and calculation of your labour cost as an employer. Handy if you want to estimate the total cost of part-time staff.

Additional hours: when is an overtime premium due?

This is one of those topics even experienced HR managers sometimes stumble over. There's a difference between "additional hours" and "overtime", and that difference determines whether you have to pay an overtime premium.

Additional hours

Additional hours are all the hours your part-time employee works above the agreed working hours, but below the full-time limit. Does someone work 20 hours a week under contract in a company with a 38-hour week? Then hours 21 to 38 are additional hours.

The employee has to agree to additional hours. You can't simply impose them, unless a sector-level CLA governs this.

The credit of additional hours (without an overtime premium)

Per reference period (usually a quarter, unless a CLA sets a different period), the part-time employee has a credit of additional hours that may be worked without entitlement to an overtime premium. In principle, that credit amounts to 12 hours per month of the reference period, so 36 hours per quarter.

Once that credit is exceeded, entitlement to an overtime premium kicks in. And that premium isn't small: a 50% supplement for additional hours on weekdays and Saturdays, and a 100% supplement on Sundays and public holidays.

Genuine overtime

Only when the additional hours exceed the full-time working hours (so above 38 hours per week in our example) do we speak of genuine overtime. The same rules then apply as for full-time employees: an overtime premium and entitlement to compensatory rest.

The pitfall? Many employers don't track additional hours properly. They only notice at the end of the quarter that the credit was long exceeded. The result: unexpected wage costs.

Read more details about overtime and compensation in Belgium in our separate article.

Holiday pay for part-time work

"Does my part-time employee get as much holiday pay as a full-time one?" No, but the system is fairer than you might think.

Number of holiday days

The number of holiday days is proportional to the number of days worked. An employee who works four days a week is entitled to 16 holiday days (instead of 20 for five days). Someone works three days? Then 12 holiday days. Logical.

Calculating holiday pay

It differs depending on whether your employee is a blue-collar or white-collar worker.

For white-collar workers: the single holiday pay is paid on the basis of the current part-time salary. The double holiday pay amounts to 92% of the gross monthly salary. If someone worked part-time for the whole previous year, the calculation is fairly straightforward.

For blue-collar workers: the holiday pay is calculated by the National Annual Holidays Office (RJV) or a holiday fund. It amounts to 15.38% of the gross wages of the holiday qualifying year (the year before). Because a part-time blue-collar worker earns less, they automatically receive less holiday pay. So the formula accounts for this itself.

Where it gets complex: when an employee switches from part-time to full-time (or vice versa) within the same company, or when someone works part-time for several employers. Then you have to prorate, and it becomes a calculation job. Want to know exactly how that works? Check out our article on calculating holiday pay.

Supplementary holiday when working hours increase

A part-time employee who increases their working arrangement by at least 20% during the holiday year compared with the average in the holiday qualifying year is entitled to supplementary holiday. That supplementary holiday only applies if the difference amounts to at least 4 holiday days. The holiday pay for those extra days is, however, deducted from holiday pay to be paid out later. So pay attention here.

Part-time work and the income guarantee benefit

As an employer, you don't have to calculate this yourself, but it's good to know how the system works. Because employees ask about it, and it sometimes influences their decision to take a part-time job.

An employee who takes a part-time job while unemployed can, under certain conditions, receive an income guarantee benefit (IGU) from the NEO (National Employment Office). This benefit tops up the part-time salary so that the total income (salary + benefit) is higher than the unemployment benefit alone.

Conditions (broadly):

• The average contractual work schedule is at most 4/5 of a full-time schedule
• The gross monthly salary is below a certain ceiling (indicatively: around 2,112 euros gross per month, an amount that is regularly indexed)
• The employee has submitted an application to the NEO via form C131A

Why this is relevant to you as an employer: employees entitled to an IGU are sometimes more inclined to accept a part-time role. So it can be an argument in your recruitment. And if an employee involuntarily moves from full-time to part-time with the same employer, a waiting period of three months applies before the IGU can start.

The five most common part-time contract mistakes

After years of experience with part-time employment, we keep seeing the same mistakes come back. Here are the five you really want to avoid.

1. No written contract (or signed too late)

The contract has to exist the moment the employee starts. Not the day after. Without a written contract, the employee can freely choose which work schedule to apply from the schedules in your work rules. And in a dispute, they'll of course pick the most favourable one.

2. Work rules not updated

Every part-time schedule that doesn't fit within the full-time framework must be included separately. And for variable schedules, you have to describe the full framework (limits, notice period, method of communication). Many sets of work rules are incomplete here.

We wrote a separate article about drawing up work rules where we explain this step by step.

3. Forgetting the deviation register

No register, no proof that your employee worked according to the agreed schedule. During an inspection by the social inspectorate, this can lead to the presumption that the employee worked full-time, with all the consequences for NSSO contributions that entails.

4. Not tracking additional hours

You regularly ask your employee to stay an hour longer. Understandable when it's busy. But if you don't record those hours, you don't know when the credit has been exceeded and an overtime premium is due. At the end of the quarter, that can be an unpleasant surprise.

5. Ignoring the one-third rule

You want someone to work only 6 hours a week, because that's all you need. But unless your sector provides an exception, that's not allowed. The minimum is one-third of full-time. Check your Joint Committee before drawing up the contract.

The part-time employment contract and your Joint Committee

The honest truth? The basic rules for part-time work are complex enough already, but it gets one layer more complicated through sector-specific deviations via Joint Committees.

Each Joint Committee can set its own rules on:

• Deviations from the minimum working hours
• The reference period for the credit of additional hours
• Specific overtime premium percentages
• Notice periods for variable schedules (shorter or longer than the statutory 5 working days)

In JC 200 (the supplementary Joint Committee for white-collar workers), the standard rules apply. But in hospitality (JC 302), construction (JC 124), or cleaning (JC 121), there are sector-level CLAs that adjust the rules. Sometimes in the employer's favour (a shorter notice period), sometimes in the employee's favour (a higher overtime premium).

At Recruit, we're active across all Belgian Joint Committees. We regularly see companies applying the standard rules while their sector has made different arrangements. That can lead both to costs that are too high and to a breach of sector obligations.

In practice: how to draw up a correct part-time contract

The key points at a glance:

• In writing and signed before work begins
• Statement of the agreed work schedule (fixed) or the average number of hours per week plus the framework (variable)
• The weekly working hours may not be lower than one-third of full-time (or one-tenth from April 2026)
• Each individual work period lasts at least 3 hours
• Include the part-time schedule in your work rules if it doesn't fit within the full-time framework
• Set up a deviation register (or use electronic time registration)
• Track additional hours and know when the credit has been used up

You can keep track of all this manually. With spreadsheets, paper registers, and a good memory. But the more part-time employees you have, the greater the chance of mistakes. A payroll system that automatically tracks work schedules, deviations, and additional hours saves you not only time but also stress during a possible inspection.

Want to know what your part-time employee is left with net? Our article on calculating gross to net gives you a clear overview.

In short

Deploying part-time staff offers flexibility, but Belgian legislation sets a solid framework against it. The minimum working hours, the obligations around work schedules and the work rules, the deviation register, the rules on additional hours and the overtime premium: each one is a point where things can go wrong if you're not careful.

The common thread? Documentation. Make sure everything is on paper (or digital): the contract, the schedules, the deviations, the additional hours. Then you're in a strong position, both during an inspection and in any dispute.

The rules are changing too. From April 2026, the one-third rule will be replaced by a one-tenth rule. That gives you more flexibility, but the other obligations remain in place. So stay up to date with the current legislation, or get support from a specialist.

Frequently asked questions

Can a part-time contract be concluded verbally?

Technically, a verbal contract isn't void, but it puts you as an employer in a weak position. Without written proof, the employee can choose the most favourable work schedule from your work rules. Always put it in writing, before employment starts.

What if my part-time employee structurally works more hours than agreed?

If it happens regularly, adjust the contract. Structurally working more than the contractual hours can lead the NSSO (or a court) to rule that the actual working hours are higher than what the contract states. With all the consequences for contributions and entitlements.

Can I convert a part-time contract into full-time?

Yes, by mutual agreement. You draw up a new contract (or an addendum to the existing one) with the new working hours. Keep in mind the impact on holiday pay and any income guarantee benefits.

Does the one-tenth rule of April 2026 change everything?

The new rule sharply lowers the minimum weekly working hours: from one-third to one-tenth of full-time. That opens the door to very small contracts (for example, 3 hours and 48 minutes per week under a 38-hour system). The minimum duration of 3 hours per work period does remain. And all other obligations (written contract, work rules, deviation register) don't change.

Is a part-time employee entitled to an end-of-year bonus?

That depends on your Joint Committee and any company-level CLAs. In many sectors, the end-of-year bonus is calculated pro rata based on the working time performed. Check the rules of your JC.

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How Recruit helps you

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• Contracts in under 60 seconds: create trial and temporary agency contracts without hassle
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• 24/7 personal support: always a dedicated contact who knows your company
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Try Recruit or get in touch with our HR experts for tailored advice.

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The information in this article is purely informative and does not replace professional legal or accounting advice. Labour legislation changes regularly. Always consult the current legislation or contact an HR expert for advice tailored to your situation. Please note: the rules can differ per Joint Committee and sector. This article provides general guidelines. For specific advice adapted to your sector, contact our HR specialists.