Reliability

Open data: the calculation parameters in JSON

Updated on 7 October 2026

The 55 parameters Indexo uses to calculate net salary and tax in Belgium, in force on 1 October 2026, are published in a JSON file, with the source and verification date of each one. You can reuse them freely, crediting Indexo (CC BY 4.0 licence).

The files

File	Contents
parametres.json	Parameters in force on 1 October 2026: machine values, readable table and sources
index.json	Catalogue: current version and list of archives
parametres-1-octobre-2026.json	Archive of one version of the parameters

Files in JSON (UTF-8). The current file changes with every parameter update; archives no longer change.

What the file contains

parametres: the exact values used by the engine (rates as decimals, amounts in euros), grouped by theme.
modules: parameters specific to certain tools (rent indexation, statutory interest rates, ceilings…), each with its value, source, verification date and status (official, forecast or to be confirmed).
tableau: one human-readable line per parameter, with its source, any cross-check and the verification date.
sources: the 110 sources cited, with the organisation and address; a secondary source is marked "secondaire": true.

Key	Theme
`onss`	Employee social security contributions
`stat`	Contributions of statutory civil servants
`bonus`	Work bonus (social and fiscal)
`pp`	Withholding tax
`ipp`	Personal income tax, 2026 income
`csss`	Special social security contribution
`exc`	Withholding tax on non-recurring pay (bonuses, holiday pay)
`onva`	Blue-collar holiday pay
`dp`	White-collar double holiday pay
`empl`	Employer social security contributions
`atn`	Company car benefit
`ot`	Overtime
`ind`	Self-employed contributions
`etu`	Students
`flexi`	Flexi-job
`smart`	Business and employment cooperative
`collab`	Sharing economy and associative work
`meal`	Meal vouchers
`volont`	Volunteering
`chom`	Unemployment
`perks`	Exempt benefits
`ded`	Tax reductions
`pub`	Public sector
`mal`	Sickness benefits
`index`	Indexation
`af`	Family allowances
`srl`	Company (SRL)

Themes in the ‘parametres’ block.

Reuse

Creative Commons Attribution 4.0 licence: free reuse, including commercial use, crediting ‘Indexo (indexo.be)’ and the version date. The values are indicative: for a legal act or a real payroll, the official source cited prevails.

Amounts and rules that are not yet official (for example an indexation forecast) are flagged as such in the table. The readable details of each parameter are also on Method and sources.

Frequently asked questions

Is the data updated?

Yes, whenever a parameter changes (indexation, new scale, published reform). The previous version is archived and remains downloadable, so you can compare the rules of different periods.

Can I use this data in an article or an app?

Yes, under the CC BY 4.0 licence: credit ‘Indexo (indexo.be)’ and the version date. For a real payroll, always check the official source given for each parameter.

Why are some sources secondary?

When an official text has not yet been published or is not easily accessible, Indexo relies on a specialist source (social secretariat, trade union) and says so. The value is replaced with the official source as soon as it is available.

What next?

Method and sourcesThe readable table of parameters and the limits of the calculation.
Proof of accuracyCases checked to the cent.
What’s changingThe calendar of rule changes.