This version is in beta - expect some breaking changes.

Individual Losses (MTD) API

Available in Sandbox Yes
Sandbox base URL
Available in Production Yes
Production base URL


This API allows developers to provide financial data for Brought Forward Losses and Loss Claims.

For Brought Forward losses a developer can:

  • provide a list of brought forward losses
  • create a new brought forward loss
  • show a single brought forward loss
  • update an existing brought forward loss
  • delete an existing brought forward loss

For Loss claims a developer can:

  • provide a list of loss claims
  • create a loss claim against an income source for a specific tax year
  • show the detail of an existing loss claim
  • update a previously entered loss claim
  • delete an existing loss claim

For information on how to connect to this API see the Income Tax MTD end-to-end service guide .


We use standard HTTP status codes to show whether an API request succeeded or not. They are usually in the range:

  • 200 to 299 if it succeeded, including code 202 if it was accepted by an API that needs to wait for further action
  • 400 to 499 if it failed because of a client error by your application
  • 500 to 599 if it failed because of an error on our server

Errors specific to each API are shown in the Endpoints section, under Response. See our reference guide for more on errors.

Single errors will be returned in the following format:
{ "code": "FORMAT_FIELD_NAME", "message": "The provided FieldName is invalid" }

Where possible, multiple errors will be returned with INVALID_REQUEST in the following format:
{ "code": "INVALID_REQUEST", "message": "Invalid request", "errors": [ { "code": "RULE_FIELD_NAME", "message": "The provided FieldName is not allowed" }, { "code": "FORMAT_FIELD_NAME", "message": "The provided FieldName is invalid" } ] }


You can use the sandbox environment to test this API. You can use the Create Test User API or it's frontend service to create test users.

It may not be possible to test all scenarios in the sandbox. You can test some scenarios by passing the Gov-Test-Scenario header. Documentation for each endpoint includes a Test data section, which explains the scenarios that you can simulate using the Gov-Test-Scenario header.

If you have a specific testing need that is not supported in the sandbox, contact our support team.

Some APIs may be marked [test only]. This means that they are not available for use in production and may change.


Some endpoints support DYNAMIC gov test scenarios. The response is dynamic based on the request parameters:

  • List Brought Forward Losses V4.0
  • Amend a Brought Forward Loss Amount V4.0
  • Amend a Loss Claim Type V4.0
  • List Loss Claims V4.0


Some endpoints support STATEFUL gov test scenarios. Stateful scenarios work with groups of endpoints that represent particular types of submissions. For each type you can POST (or PUT) to submit or amend data, GET to retrieve or list data and DELETE to delete data. For example, with a STATEFUL gov test scenario a retrieval will return data based on what you submitted.

The following groups are stateful in the sandbox:

  • Brought Foward Losses V4.0
  • Loss Claims V4.0

Fraud Prevention



View API endpoints
Why do these endpoints look different?

The endpoints for this API now use the Open API Specification (OAS).

The API has not changed. You do not need to make any updates to your application if you already use this API.