Stamp Duty Land Tax (SDLT) API

The Stamp Duty Land Tax (SDLT) API provides accurate calculations for stamp duty taxes on property purchases in England and Northern Ireland using the latest 2026 rates. Our API handles all buyer types, surcharges, and property types with detailed breakdown calculations.

This API provides:

• Residential property SDLT calculations with 2026 rates
• Commercial property SDLT calculations
• First-time buyer relief calculations
• Additional property surcharge (5%)
• Non-UK resident surcharge (2%)
• Detailed breakdown by tax bands

Current 2026 SDLT Rates:

This API is ideal for:

• Conveyancing software requiring automated SDLT calculations
• Estate agents providing purchase cost estimates
• Mortgage brokers calculating total transaction costs
• Property investment platforms showing tax implications
• Financial advisors and accountants
• Property portals displaying stamp duty costs

All requests to the SDLT API require authentication using an API key. You can obtain your API key from your PropertyInsights dashboard after subscribing to an API plan.

Include your API key in the request header as follows:

X-API-Key: your_api_key_here

Base URL

https://propertyinsights.co.uk/api/v1/

/sdlt/calculate

POST /sdlt/calculate

Send parameters as JSON in the request body.

Successful chargeable JSON responses include a top-level billing object. The endpoint examples on this page focus on the endpoint-specific data, so this repeated block may not be shown in every example.

"billing": {
  "mode": "prepaid",
  "creditsCharged": 1,
  "creditsRemaining": 1999,
  "creditsRefreshAt": "2026-08-14T09:30:00.000Z"
}

All authenticated API-key calls expose the billing headers, including validation errors and zero-credit status or management requests. Only successful chargeable JSON responses add the billing object to the response body.

All API responses are returned in JSON format. The standard response structure is as follows:

{
  "success": boolean,
  "data": {
    // Response data varies by endpoint
  },
  "error": {
    "code": string,
    "message": string
  } // Only present if success is false
}

Successful SDLT Calculation Response

{
  "success": true,
  "data": {
    "propertyPrice": 500000,
    "propertyType": "residential",
    "firstTimeBuyer": true,
    "higherRate": false,
    "ukResident": true,
    "stampDuty": 10000,
    "breakdown": [
      {
        "band": "£0 - £300,000",
        "rate": "0%",
        "amount": 0
      },
      {
        "band": "£300,000 - £500,000",
        "rate": "5.0%",
        "amount": 10000
      }
    ],
    "surcharges": {
      "additionalProperty": 0,
      "nonUkResident": 0
    }
  }
}

Response Fields

The API uses standard HTTP response codes and returns detailed error information in JSON format. All errors follow a consistent structure to help you handle them appropriately in your application.

Error Response Format

{
  "success": false,
  "error": {
    "code": "INVALID_PROPERTY_TYPE",
    "message": "Property type must be \"residential\" or \"commercial\"."
  }
}

API requests are subject to rate limiting based on your subscription plan. The current limits are:

When you exceed your rate limit, the API will return a 429 Too Many Requests response. Each response includes the following headers to help you track your usage:

X-RateLimit-Limit: [requests-per-minute limit]
X-RateLimit-Remaining: [requests remaining in current window]
X-RateLimit-Reset: [timestamp when limit resets]