Claim language

R&D tax credit glossary

Quick definitions for the terms that appear in UK R&D tax credit research, calculators, and claim preparation.

Start with the calculator if you want to estimate potential value, then use this page to decode the claim terms.

• AIF

  Additional Information Form. HMRC requires this extra R&D claim form to be submitted before, or on the same day as, the Company Tax Return for the claim.

• Additional Information Form

  The form used to give HMRC project descriptions, qualifying cost categories, and claim contact details before the R&D tax relief claim is processed.

• ERIS

  Enhanced R&D Intensive Support. A route for eligible loss-making R&D-intensive SMEs for accounting periods beginning on or after 1 April 2024.

• Merged Scheme

  The main R&D relief route for accounting periods beginning on or after 1 April 2024, using an expenditure credit approach.

• RDEC

  Research and Development Expenditure Credit. The credit-style R&D relief approach used in the merged scheme.

• R&D intensity

  A ratio comparing qualifying R&D expenditure with total relevant expenditure. It matters when considering ERIS eligibility.

• CT600

  The UK Company Tax Return. R&D tax relief claims are made through the Corporation Tax return process.

• CT600L

  A supplementary Company Tax Return form used for R&D expenditure credit claims.

• Qualifying expenditure

  Costs that can be connected to qualifying R&D work, such as relevant staff, consumables, software, data, cloud, contractors, or externally provided workers, subject to scheme rules.

• PAYE cap

  A limit connected to the company's PAYE and National Insurance liabilities. It can restrict payable R&D credits.