Guidance

Self Assessment technical specifications (2025) for individual returns

Use this technical documentation for individual returns if you're a software developer working with the Self Assessment online service.

• From: HM Revenue & Customs
• Published: 22 October 2024
• Last updated: 15 July 2025
  Show all updates

  1. 15 July 2025

     The attachment 'Special cases version 2.0a' has been added.

  2. 21 May 2025

     The attachments 'Special cases version 1.0a' and 'Exclusion cases version 1.0a' have been added.

  3. 20 May 2025

     The attachments 'Special cases version 0.1a' and 'Exclusion cases version 0.1a' have been updated.

  4. 19 March 2025

     The attachments 'MTR Mapping version 1.1', 'Special cases version 0.1a' and 'Exclusion cases version 0.1a' have been added. The attachments 'Calculate Tax and NIC MTR version 2.4.0a', 'Calculate Tax and NIC MTR version 2.4.1a — Annex C', 'Test Case generator (Tester) MTR version 2.4.0' and 'Test Case Generator (Tester) MTR version 2.4.1' have been updated.

  5. 21 February 2025

     The attachments 'Calculate Tax and NIC MTR version 2.3.0a' and 'Test Case generator (Tester) MTR version version 2.3.0' has been added.

  6. 31 January 2025

     The attachments 'Calculate Tax and NIC MTR version 2.3.1a', 'Payments on Account (Stage 13) Tax and NIC calculation version 1.0.0a' and 'Test Case Generator (Tester) MTR version 1.3.0' have been added.

  7. 22 October 2024

     First published.

Documents

Self Assessment Individual RIM Artefacts version 1.0

ZIP, 4.81 MB

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Calculate Tax and NIC MTR version 2.4.0a

ODT, 552 KB

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Calculate Tax and NIC MTR version 2.4.1a — Annex C

ODT, 601 KB

This file is in an OpenDocument format

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Payments on Account (Stage 13) Tax and NIC calculation version 1.0.0a

ODT, 8.34 KB

This file is in an OpenDocument format

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Test Case generator (Tester) MTR version 2.4.0

3.54 MB

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Test Case Generator (Tester) MTR version 2.4.1

3.59 MB

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MTR Mapping version 1.1

ZIP, 23.3 KB

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Special cases version 2.0a

ODT, 46.3 KB

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Exclusion cases version 1.0a

ODT, 38.1 KB

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Details

You should use this technical documentation for individual returns if you’re a software developer working with the Self Assessment online service.