Checking the indexation on a cleaning contract means testing the announced percentage against your own indexation clause before you approve the invoice. It is not the collective labour agreement (CLA) that determines what reaches your invoice, but the formula in your contract. GRIP is contract management software for the supplier contracts of organisations in healthcare, education and the public sector. According to WorldCC, PwC and McKinsey, an average of 2.6% of contract value leaks away each year through poor contract management, and 95% of organisations have no complete view of their own contractual obligations. An incorrect indexation is exactly that kind of leak.
An indexation letter of 6.2% is sitting on your desk. The cleaning supplier points to the new CLA and wants to pass on the increase from 1 January. Does that percentage match your contract? For many contract managers the answer is: no idea, and no time to find out. Below you will read how to run that check in minutes.
The 2026-2028 cleaning CLA affects your invoice, but not how you think
The CLA booklet for the cleaning and window-cleaning sector 2026-2028 was published in October 2026. In Belgium, wages in joint committee 121 (cleaning) rose by 2.07% in July 2026. According to CBS figures on the service sector, labour costs make up by far the largest share of the cost price for labour-intensive services. A CLA increase therefore weighs directly on your supplier’s cost structure.
This is where the thinking goes wrong. A CLA rise is not an invoice rise. What reaches your invoice is determined not by the CLA, but by the indexation clause in your contract. If that clause holds a weighted formula with wages, social charges and a general price index, the contractual increase is almost always lower than the bare CLA wage rise. Suppliers sometimes reach for the highest figure available. Your job is to bring the figure back to what was contractually agreed.
Why you should not simply approve the indexation
Many contract managers sign off the indexation letter because the deadline is pressing and the clause sits in a PDF somewhere on a drive. Tracking it down costs half an afternoon you do not have. The result: a percentage that is never checked against the source, year after year.
The solution does not start with a stricter clause, but with a fixed checking routine you can run in minutes. It comes down to two questions. Does the percentage match the chosen index and the reference dates? And is the base correct, meaning do you pay indexation on the right contract amount rather than on a quietly expanded scope? Without an answer to both questions, approving is a gamble.
Reading your indexation clause: six fields that decide whether it is correct
Take out your clause and fill in these six fields. Only when they all match the supplier’s letter is the indexation correct.
- Chosen index. Which index does your contract prescribe? A CLA wage index, the CBS price index, or a composite formula. The supplier must use exactly this index.
- Reference month. Which month or period is the index figure taken from? Often October on October, sometimes an annual average.
- Reference date. The date on which the index figure is set. A shifted reference date gives a different percentage.
- Publication date. When was the source index figure officially published? You cannot index on a figure that did not yet exist.
- Effective date. From when does the new rate apply? Usually 1 January, but check it.
- Weightings and cap. With a weighted formula: what percentage weight goes to wages, social charges and other? And is there a maximum increase?
Composite indexation worked out: 70% wages, 10% social charges, 20% other
Say you have a cleaning contract of 10,000 euros per month. The clause weights 70% wages, 10% social charges and 20% general price index. The figures for your reference period: wages +5.0%, social charges +3.0%, other +2.5%.
- Wages: 70% x 5.0% = 3.50%
- Social charges: 10% x 3.0% = 0.30%
- Other: 20% x 2.5% = 0.50%
- Weighted indexation: 4.30%
The contractual increase is 4.30%, not 5.0%. Your new monthly rate becomes 10,430 euros, not 10,500 euros. That difference of 70 euros per month is 840 euros per year on this one contract. Across twenty sites it adds up fast.
Where does it go wrong? Two places. Rounding: anyone who rounds each sub-percentage separately before adding up ends up with a different final figure than someone who rounds only at the end. Record when you round. And reference dates: if the supplier takes a more recent, higher wage figure than your contract prescribes, the difference feeds straight through into the 70% component. Always request the source index figures the supplier used.
Indexation, additional work or a scope change? Pull them apart
The invoice rises, but is that indexation? Sometimes frequencies have quietly gone up or square metres have been added. A higher invoice labelled “indexation” while scope is hidden inside it is the most common error in practice. These three should appear separately on your invoice.
- Indexation. The same work, a higher rate according to your clause.
- Additional work. One-off extra work, agreed separately, with its own work order.
- Scope change. Structurally more or fewer rooms, frequencies or square metres, with an adjusted base.
If you see an invoice line that mixes these three together, send it back and ask for a breakdown. You always calculate indexation on the original base, not on a base already inflated by scope.
What to do with an error: wrong index, too late, or retroactive
If the announcement only arrives in March with an effective date of 1 January, check whether your contract allows retroactive application. If that basis is missing, the new rate only applies from the announcement. If the supplier uses a different index than agreed, or a year-on-year figure instead of the prescribed period, do not approve. Request a corrected letter with the right basis. No basis, no payment of the difference.
Recording the check: from a loose PDF to a single contract file
A check you record nowhere, you have to repeat next year. In Excel the clause lives on one tab, the letter in a mailbox and the index figure in your head. Instead, link them together in one file: the clause, the indexation letter, the source index figures used, your own calculation and the approval, with an audit trail showing who approved what and when.
With the Contract Dashboard your indexation clause sits next to the invoice, and the financial management calculates the weighted formula for you. That lets you show your CFO that an incorrect indexation does not slip through unnoticed across all your sites.
See how GRIP records the indexation check for your cleaning contracts. Book a demo.
Frequently asked questions
Can a cleaning company apply indexation retroactively? Only if your contract explicitly allows it. If the announcement arrives later than the effective date and there is no basis for retroactive application, the new rate only applies from the date of the announcement.
Is the CLA wage increase the same as my contractual indexation? No. The CLA determines your supplier’s labour costs. What reaches your invoice is determined by your indexation clause. With a weighted formula, the contractual increase is usually lower than the bare CLA wage rise.
Which percentage applies after the 2026-2028 cleaning CLA? That depends on your clause, not on the CLA itself. The 2026-2028 CLA was published in October 2026; in Belgium PC 121 rose by 2.07% in July 2026. You calculate your own percentage with your chosen index and weightings.
How do I know whether an invoice increase is indexation or scope? Indexation, additional work and scope change belong separately on the invoice. If you cannot tell them apart, ask for a breakdown. You always calculate indexation on the original base.
What do I do if the supplier uses the wrong index? Do not approve, and request a corrected letter with the index, reference month and reference date your contract prescribes. Only pay the difference once the basis is correct.
How do I set up an indexation check for an audit? Keep the clause, the indexation letter, the source index figures used, your calculation and the approval in one contract file with an audit trail. That way every decision can be traced later.