how do I compare the pay of part-time employees with full-time colleagues

Compare part-time and full-time employees on an hourly basis

When comparing the pay of a part-time and full-time employee, you do not look at the amount someone receives monthly in their account, but at what they earn per hour. A part-time employee working three days and a full-time employee working five days can therefore be compensated equally even though the monthly salary varies considerably — that difference is purely in the scope of the employment contract, not in the compensation itself. What matters is the hourly rate, and in addition all other components of compensation on a pro-rata basis: a bonus, allowance or other benefit that someone receives, counts in proportion to the scope of the contract.

This comparison on an hourly basis only works well if it is first clear which functions you are actually comparing with each other. A part-time and full-time employee are only in the same comparison if they perform work of equal value; how you determine this is described under how you determine which functions are equivalent. It is also important to establish in advance what falls under "compensation" in the comparison — not only the basic salary, but also components such as a company car or a thirteenth month can count, as described under what counts as compensation.

Why this follows from the Directive

Article 3 of Directive (EU) 2023/970 defines compensation broadly, including base pay and all other benefits, which forms the basis for reducing employment contracts of different scope to a common denominator — the hourly rate. Article 4 of the Directive links the comparison to work of equal value, regardless of the scope of the contract, and Article 9 stipulates that the report is prepared per category of employees, where the scope of the employment contract is not a reason to place someone outside that category.