B2B Tax Calculator API

Endpoints

Quick Example

curl "https://rel.tax/v1/calculate/de?income=60000"

POST Example

curl -X POST https://rel.tax/v1/calculate/us \
  -H "Content-Type: application/json" \
  -d '{"income": 100000, "qbiDeduction": true}'

All endpoints return JSON. CORS enabled for all origins. No authentication required.

Supported Countries

50 countries live. Click any card to see full parameter docs below.

GET /v1/calculate/pl?income=10000&taxationType=lumpsum&lumpSumRate=12

GET /v1/calculate/nz?income=75000

GET /v1/calculate/au?income=100000

GET /v1/calculate/gb?income=50000

GET /v1/calculate/us?income=100000

GET /v1/calculate/ca?income=100000&province=ON

GET /v1/calculate/de?income=60000

GET /v1/calculate/es?income=40000

GET /v1/calculate/ee?income=60000

GET /v1/calculate/jp?income=5000000
GET /v1/calculate/jp?income=10000000&blueReturn=none&businessTaxRate=3

GET /v1/calculate/rs?income=60000
GET /v1/calculate/rs?income=50000&taxModel=pausalac&pausalnaOsnovica=50000

GET /v1/calculate/ge?income=100000
GET /v1/calculate/ge?income=100000&taxRegime=regular&expenses=20000

GET /v1/calculate/am?income=50000000&taxRegime=turnover_it
GET /v1/calculate/am?income=20000000&taxRegime=turnover_it

GET /v1/calculate/mx?income=1000000
GET /v1/calculate/mx?income=500000&taxRegime=general&expenses=100000

GET /v1/calculate/pt?income=60000
GET /v1/calculate/pt?income=60000&accountingRegime=organized&expenses=15000

GET /v1/calculate/bg?income=60000
GET /v1/calculate/bg?income=60000&activityType=sole_trader&expenses=20000

GET /v1/calculate/cz?income=1000000
GET /v1/calculate/cz?income=1000000&expenseMethod=flat_80
GET /v1/calculate/cz?income=1000000&expenseMethod=actual&expenses=300000

GET /v1/calculate/ro?income=120000&expenses=20000
GET /v1/calculate/ro?income=120000&entityType=srl_micro

GET /v1/calculate/ae?income=500000&entityType=freezone&expenses=50000

GET /v1/calculate/me?income=60000&expenses=5000

GET /v1/calculate/cy?income=80000&expenses=5000

GET /v1/calculate/sg?income=120000&expenses=10000

GET /v1/calculate/hr?income=60000&expenses=10000&taxModel=obrt
GET /v1/calculate/hr?income=35000&taxModel=pausalni

GET /v1/calculate/hu?income=12000000&taxModel=kata
GET /v1/calculate/hu?income=12000000&taxModel=ev&expenses=2000000

GET /v1/calculate/nl?income=60000
GET /v1/calculate/nl?income=60000&starter=true

GET /v1/calculate/th?income=1200000
GET /v1/calculate/th?income=100000&incomePeriod=monthly&vatRegistered=true

GET /v1/calculate/my?income=120000
GET /v1/calculate/my?income=10000&incomePeriod=monthly

GET /v1/calculate/cr?income=24000000
GET /v1/calculate/cr?income=24000000&expenses=5000000

GET /v1/calculate/id?income=1000000000&taxModel=umkm
GET /v1/calculate/id?income=300000000&taxModel=progressive

GET /v1/calculate/co?income=100000000
GET /v1/calculate/co?income=100000000&expenses=20000000

GET /v1/calculate/be?income=80000
GET /v1/calculate/be?income=80000&expenses=15000

GET /v1/calculate/fr?income=60000&taxModel=micro_bnc
GET /v1/calculate/fr?income=60000&taxModel=versement_liberatoire

GET /v1/calculate/ph?income=1500000&taxModel=flat_8
GET /v1/calculate/ph?income=1500000&taxModel=graduated

GET /v1/calculate/it?income=60000&taxModel=forfettario
GET /v1/calculate/it?income=60000&taxModel=ordinario

GET /v1/calculate/lt?income=60000

GET /v1/calculate/gr?income=60000

GET /v1/calculate/ie?income=80000

GET /v1/calculate/at?income=80000

GET /v1/calculate/se?income=600000

GET /v1/calculate/il?income=300000

GET /v1/calculate/in?income=3000000&taxModel=presumptive
GET /v1/calculate/in?income=2000000&taxModel=new_regime

GET /v1/calculate/dk?income=600000

GET /v1/calculate/fi?income=60000

GET /v1/calculate/no?income=700000

GET /v1/calculate/ch?income=120000

GET /v1/calculate/lv?income=40000
GET /v1/calculate/lv?income=30000&taxModel=micro

GET /v1/calculate/sk?income=60000

GET /v1/calculate/si?income=80000&taxModel=normiranec
GET /v1/calculate/si?income=60000&taxModel=standard

GET /v1/calculate/mt?income=50000

GET /v1/calculate/tr?income=500000

Response Format

All /v1/calculate/:country endpoints return a consistent JSON structure with country-specific details.

Response Structure

{
  "country": "de",
  "taxYear": 2025,
  "input": { /* echoed input parameters */ },
  "monthly": {
    "gross": 5000.00,
    "vat": 0,
    "grossWithVat": 5000.00,
    "socialInsurance": 846.89,
    "healthInsurance": 0,
    "incomeTax": 671.83,
    "totalDeductions": 1518.72,
    "net": 3481.28
  },
  "yearly": {
    "gross": 60000.00,
    "socialInsurance": 10162.68,
    "healthInsurance": 0,
    "incomeTax": 8061.92,
    "totalDeductions": 18224.60,
    "net": 41775.40
  },
  "rates": {
    "effectiveTaxRate": 0.3037,
    "dailyRate": 189.03,
    "hourlyRate": 23.63,
    "workingDays": 221
  },
  "details": { /* country-specific calculation details */ }
}

Field Reference

Error Response

{ "error": "income is required and must be a positive number" }

Errors return HTTP 400 with a descriptive message. Unsupported country codes return HTTP 404.

Agent Integration Guide

Instructions for AI agents that need to calculate taxes programmatically.

MCP Server (Claude Desktop / Claude Code)

Use rel.tax as a native tool in Claude Desktop or Claude Code via Model Context Protocol:

npx @sliday/reltax

Add to your Claude Desktop config (claude_desktop_config.json):

{
  "mcpServers": {
    "reltax": {
      "command": "npx",
      "args": ["@sliday/reltax"]
    }
  }
}

Three tools are available:

• reltax_list_countries — List all 50 supported countries
• reltax_get_country_info — Get tax parameters for a country
• reltax_calculate_tax — Calculate B2B taxes with full breakdown

Auto-Import

Import the OpenAPI 3.1 spec into your framework of choice:

• LangChain — OpenAPIToolkit.from_openapi_spec(url)
• OpenAI function calling — import as tool definitions
• Claude tool use — convert paths to tool schemas
• ChatGPT Plugin — discovered via /.well-known/ai-plugin.json

Step 1: Determine the Country

Use the two-letter ISO country code. Call /v1/countries for the full list of 50 supported countries.

Step 2: Build the Request

Only income is required. All other parameters have sensible defaults. Use GET with query params for simplicity:

GET https://rel.tax/v1/calculate/de?income=75000&churchTax=9

Step 3: Parse the Response

The key fields you likely need:

• yearly.net — annual take-home pay
• monthly.net — monthly take-home pay
• rates.effectiveTaxRate — total tax burden as decimal
• rates.hourlyRate — effective hourly rate after all deductions
• yearly.totalDeductions — total annual taxes and contributions

Tips

• Income is always in the country's local currency unless the country supports currency selection (Serbia: EUR or RSD)
• All countries support incomePeriod (monthly/yearly). Poland defaults to monthly; most others default to yearly
• To compare countries, normalize to yearly income first
• The details object contains intermediate calculation values useful for explaining results
• Fetch /v1/countries/:code for machine-readable parameter docs at runtime