Tax Calculator API

Authentication

All API requests require a Bearer token in the Authorization header.

Authorization: Bearer sltax_t2_your_api_key_here

Token Format

API keys follow the format sltax_t2_<random> where t2 identifies the token version. Keys are issued per-tenant and scoped to your account.

Get an API Key

Quick Start

Calculate surplus lines tax for a $50,000 premium in Texas with a single API call:

curl -X POST https://api.sltax360.com/api/v1/calculator/estimate \
  -H "Authorization: Bearer sltax_t2_your_api_key_here" \
  -H "Content-Type: application/json" \
  -d '{
    "state": "TX",
    "premium": 50000,
    "policy_fees": 500
  }'

The response includes an itemized breakdown of every tax and fee:

{
  "success": true,
  "data": {
    "state": { "id": 44, "code": "TX", "name": "Texas" },
    "input": { "premium": 50000, "policy_fees": 500, "effective_date": "2026-02-26" },
    "tax_base": 50500,
    "line_items": [
      { "name": "Surplus Lines Tax", "code": "sl_tax", "rate": 4.85, "rate_type": "percentage", "amount": 2449.25 },
      { "name": "Stamping Fee", "code": "stamping_fee", "rate": 0.075, "rate_type": "percentage", "amount": 37.88 }
    ],
    "rounding_rule": "standard",
    "total_taxes_and_fees": 2487.13,
    "total_due": 52987.13,
    "special_notes": "Texas: 4.85% SL tax, 0.075% stamping fee to SLTX. Tax is on total gross premium including policy fees.",
    "calculated_at": "2026-02-26T15:30:45+00:00"
  },
  "meta": {
    "timestamp": "2026-02-26T15:30:45Z",
    "request_id": "req_a1b2c3d4e5f6",
    "response_time_ms": 45
  }
}

POST /estimate

Calculate surplus lines taxes and fees for a given state and premium amount. Returns an itemized breakdown of all applicable taxes and fees.

Request Parameters

Send as JSON request body.

Response Fields

Line Item Codes

Not all codes appear for every state. The response only includes line items applicable to the requested state.

Fee Types (for fees array)

When using the fees array, each fee is categorized for per-state tax base inclusion:

Example with fees array

{
  "state": "TX",
  "premium": 50000,
  "fees": [
    { "type": "policy_fee_company", "amount": 250 },
    { "type": "broker_fee", "amount": 150 },
    { "type": "inspection_fee", "amount": 100 },
    { "type": "filing_fee", "amount": 25 }
  ]
}

For Texas, the tax_base = $50,000 + $250 (policy) + $150 (broker) + $100 (inspection) = $50,500. The $25 filing fee is pass-through (not taxed). The response includes a fee_breakdown showing exactly which fees were taxed.

Response Format

All responses use a consistent JSON envelope with success, data/error, and meta fields.

Success Response

{
  "success": true,
  "data": { /* endpoint-specific data */ },
  "meta": {
    "timestamp": "2026-02-26T15:30:45Z",
    "request_id": "req_a1b2c3d4e5f6",
    "response_time_ms": 45
  }
}

Error Response

{
  "success": false,
  "error": {
    "code": "VALIDATION_ERROR",
    "message": "Validation failed",
    "details": { /* field-level errors when applicable */ }
  },
  "meta": { /* same as success */ }
}

Meta Object

Error Codes

Validation Error Example

{
  "success": false,
  "error": {
    "code": "VALIDATION_ERROR",
    "message": "Validation failed",
    "details": {
      "fields": {
        "state": ["must be exactly 2 characters"],
        "premium": ["must be greater than 0.01"]
      }
    }
  }
}

Rate Limits

API requests are rate-limited per API key on a per-hour basis. Limits vary by plan tier.

Response Headers

Limits by Plan

State-Specific Rules

Each state has unique tax rules that the API handles automatically. Here are the key concepts:

Tax Base Composition

Some states include policy fees in the tax base; others tax only the premium. The API determines this automatically based on the state — you just provide both values.

Rounding Rules

Complexity Spectrum

States range from simple (1-2 line items) to complex (5+ fees). Two examples:

Code Examples

• cURL
• JavaScript
• Python

curl -X POST https://api.sltax360.com/api/v1/calculator/estimate \
  -H "Authorization: Bearer sltax_t2_your_api_key_here" \
  -H "Content-Type: application/json" \
  -d '{
    "state": "FL",
    "premium": 75000,
    "policy_fees": 250,
    "effective_date": "2026-03-01"
  }'

const response = await fetch('https://api.sltax360.com/api/v1/calculator/estimate', {
  method: 'POST',
  headers: {
    'Authorization': 'Bearer sltax_t2_your_api_key_here',
    'Content-Type': 'application/json',
  },
  body: JSON.stringify({
    state: 'FL',
    premium: 75000,
    policy_fees: 250,
    effective_date: '2026-03-01',
  }),
});

const result = await response.json();

if (result.success) {
  console.log('Total due:', result.data.total_due);
  result.data.line_items.forEach(item =>
    console.log(`  ${item.name}: $${item.amount}`)
  );
} else {
  console.error('Error:', result.error.message);
}

import requests

response = requests.post(
    "https://api.sltax360.com/api/v1/calculator/estimate",
    headers={
        "Authorization": "Bearer sltax_t2_your_api_key_here",
        "Content-Type": "application/json",
    },
    json={
        "state": "FL",
        "premium": 75000,
        "policy_fees": 250,
        "effective_date": "2026-03-01",
    },
)

result = response.json()

if result["success"]:
    data = result["data"]
    print(f"Total due: ${data['total_due']:,.2f}")
    for item in data["line_items"]:
        print(f"  {item['name']}: ${item['amount']:,.2f}")
else:
    print(f"Error: {result['error']['message']}")

Getting Started