Tax Calculator API Documentation

Authentication

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

HTTP 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.

Security: Never expose API keys in client-side code, public repositories, or browser requests. Always make API calls from your server.

Get an API Key

Quick Start

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

cURL

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:

Response — 200 OK

{
  "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
  }
}

Try it free: Test calculations interactively with our free online tax calculator before integrating the API.

POST /estimate

POST /api/v1/calculator/estimate Authenticated

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.

Parameter	Type	Description
`state` required	string	2-letter state code (e.g., `"TX"`, `"CA"`, `"FL"`)
`premium` required	number	Premium amount in USD. Must be greater than 0.01.
`policy_fees` optional	number	Policy fees in USD. Defaults to `0`. Some states include fees in the tax base.
`effective_date` optional	string	Date in `YYYY-MM-DD` format for rate lookup. Defaults to today. Use for historical calculations.

Response Fields

Field	Type	Description
`state`	object	State info: `id`, `code`, `name`
`input`	object	Echo of your input parameters
`tax_base`	number	Computed tax base (premium, or premium + fees depending on state rules)
`line_items`	array	Itemized list of taxes and fees. Each item has `name`, `code`, `rate`, `rate_type`, `amount`, `unrounded_amount`
`rounding_rule`	string	State rounding rule: `standard`, `whole_dollar`, or `no_rounding`
`total_taxes_and_fees`	number	Sum of all line item amounts
`total_due`	number	Premium + policy fees + total taxes and fees
`special_notes`	string\|null	State-specific notes or caveats, if any
`calculated_at`	string	ISO 8601 timestamp of the calculation

Line Item Codes

Code	Name	Rate Type	Description
`sl_tax`	Surplus Lines Tax	percentage	Primary state surplus lines tax
`stamping_fee`	Stamping Fee	percentage	Stamping office processing fee
`fire_marshal`	Fire Marshal Tax	percentage	State fire marshal assessment
`figa`	FIGA Assessment	percentage	Guaranty association assessment
`service_fee`	Service Fee	percentage	State service/processing fee
`surcharge`	State Surcharge	percentage	Additional state surcharge
`regulatory_fee`	Regulatory Fee	percentage	Regulatory compliance fee
`slas_fee`	SLAS/Clearinghouse Fee	percentage	Clearinghouse or SLAS fee
`municipal_tax`	Municipal Tax	percentage	City or local jurisdiction tax
`flat_fee`	Filing Fee	flat	Fixed dollar filing fee

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

Response Format

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

Success Response

Success envelope

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

Error Response

Error envelope

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

Meta Object

Field	Description
`timestamp`	ISO 8601 timestamp of the response
`request_id`	Unique request identifier for debugging. Include this in support requests.
`response_time_ms`	Server-side processing time in milliseconds

Error Codes

HTTP Status	Error Code	Description
`400`	`BAD_REQUEST`	Malformed request or invalid state code
`401`	`UNAUTHORIZED`	Missing or invalid API key
`403`	`FORBIDDEN`	Tax Calculator feature not enabled for your plan
`404`	`NOT_FOUND`	Endpoint not found
`405`	`METHOD_NOT_ALLOWED`	Wrong HTTP method (e.g., GET on POST-only endpoint)
`422`	`VALIDATION_ERROR`	Request parameters failed validation. Check `details.fields`.
`429`	`RATE_LIMIT_EXCEEDED`	Too many requests. Retry after the period in the response.
`500`	`INTERNAL_ERROR`	Unexpected server error. Contact support with `request_id`.

Validation Error Example

422 Validation Error

{
  "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

Header	Description
`X-RateLimit-Limit`	Maximum requests allowed per hour
`X-RateLimit-Remaining`	Requests remaining in the current window
`X-RateLimit-Reset`	Unix timestamp when the limit resets

Limits by Plan

Plan	Requests / Hour
Professional	500
Enterprise	5,000

Best practice: Cache results when the same state + premium + fees combination is requested repeatedly.

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.

The API automatically determines whether policy fees are included in the tax base for each state — just provide both premium and policy_fees values.

Rounding Rules

Rule	Behavior	Example
`standard`	Round to nearest cent	$1,515.456 → $1,515.46
`whole_dollar`	Round to whole dollar	$1,515.456 → $1,515.00
`no_rounding`	Full precision (5 decimals)	$1,515.45600

Complexity Spectrum

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

Wyoming (Simple)

Surplus Lines Tax: 3.0%

Florida (Complex)

Surplus Lines Tax: 4.94%
Stamping Fee: 0.06%
Fire Marshal Tax: 1.0% (fire/allied lines)
FIGA Assessment: 0.5%
Service Fee: 0.1%
Municipal Tax (if applicable)

Code Examples

cURL

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"
  }'

JavaScript (fetch)

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);
}

Python (requests)

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

1

Get API Key

Contact us to receive your API credentials

2

Test Calculator

Try the free online calculator first

3

First API Call

Use the Quick Start example above

4

Integrate

Use code examples in your language

Get API Key Try Free Calculator

Need help? Email us at support@sltax360.com with your request_id for fastest resolution.