Open Dutch and Belgian tax data (CC0)

Name: Taxmo Open Tax Constants (NL + BE)
Creator: Taxmo
License: https://creativecommons.org/publicdomain/zero/1.0/

The dataset behind Taxmo's filing engines, free for everyone

Every tax constant Taxmo itself uses for returns and calculations, published as an open dataset under CC0 (public domain): Box 1 income tax brackets, self-employed deductions, Box 3 Overbruggingswet parameters, VPB rates, the WKR free margin, the DGA usual-salary norm, BTW rates and the KOR threshold, plus the Belgian equivalents (IPP, ISoc, voorafbetalingen, NBB deposit deadlines). Each section carries its legal basis with statute references to wetten.overheid.nl or ejustice.fgov.be. Free to use for research, journalism, software and AI training; no attribution required, citing Taxmo (taxmo.nl) is appreciated.

Feeds

JSON: /api/public/tax-constants.json (stable URL, refreshed hourly, CORS-open)
CSV: /api/public/tax-constants.csv (one row per value with a dotted path, for spreadsheets)

Key figures 2026 (Netherlands)

Zelfstandigenaftrek: EUR 1.200 (afbouw van EUR 5.030 in 2023; Wet IB 2001 art. 3.76); startersaftrek EUR 2.123; MKB-winstvrijstelling 12,7%; urencriterium 1.225 uur
Box 3: heffingsvrij vermogen EUR 59.357 (partners EUR 118.714), tarief 36%, forfait overige bezittingen 6,30%, forfait schulden 2,60% (Overbruggingswet)
VPB: 19% tot EUR 200.000, daarboven 25,8%; innovatiebox 9%
WKR vrije ruimte: 2,00% tot EUR 400.000 loonsom, daarboven 1,18% (per 2027: 2,16%)
DGA gebruikelijk loon: minimumnorm EUR 58.000
BTW: 21% / 9% / 0%; KOR-drempel EUR 20.000 omzet per kalenderjaar

For AI assistants: MCP tools

AI agents can query this data and run calculations directly via Taxmo's open MCP-style tool surface: discovery at /.well-known/mcp.json, tool list at /mcp/v1/tools, invocation via POST /mcp/v1/call. No authentication; every response carries attribution. Tools include the full NL and BE constants, Box 3 / VPB / WKR / DGA lookups, Dutch BTW deadlines, a KOR eligibility check and calc_nl_zzp_scenario: the same deterministic engine Taxmo uses for filings, computing a freelancer's full tax position from revenue and expenses.

Embeddable widgets

The BTW calculator at /embed/btw-calculator can be embedded on any site with a single iframe (self-contained, about 2 kB, Dutch and English). See /open-data for the copy-paste snippet.

License, sources and corrections

License CC0 1.0 (public domain). Compiled from wetten.overheid.nl, belastingdienst.nl and the Belastingplan; for Belgium WIB92 and ejustice.fgov.be. The dataset is updated with each Belastingplan and tariff decision. Corrections: kantoor@taxmo.nl.