IAS23043 Business Tax- R&D RDEC CT600 L55/Tax Comp incorrect value of notional tax (19% v 25%) FIXED

ias23043-business-tax-rd-rdec-ct600-l55-tax-comp-incorrect-value-of-notional-tax-19-v-25

IAS23043 Business Tax- R&D RDEC CT600 L55/Tax Comp incorrect value of notional tax (19% v 25%) FIXED

25th November 2025

NOTE: If you are now on IRIS Version 26.1.0 or later and you believe the calculation is still incorrectly calculated at 19% and it should be 25%. Our Development team has checked and that you run the Tax comp – if the ‘Profits chargeable to Corporation tax is NIL’ then therefore it is calculated at the correct 19% and following HMRC rules.

If you have a CTAP period that starts prior to the start of the RDEC Merged Scheme. Therefore the calculation of notional tax should be using 25%.

1.The R&D RDEC entry screens will be correct

2. The Tax comp has a RDEC adjustment that is calculated at a incorrect rate of 19% (should be 25%)

3. The CT00L Box L55 may be showing a value using a rate of 19% incorrectly (should be 25%)

4. The RDEC credit calc should be a mix of 19% and 25% but its all calculated incorrectly at 19%

5. There are incorrect carry forward values

This is a DEFECT and our IRIS Development Team have released a HOTFIX version 25.4.8 OR just update to the latest IRIS version as these later versions will include the HOTFIX. (Prior advise before version 26.1.0 was to contact IRIS Support and request this hotfix link be sent to you which is no longer relevant)

Our apologies for the inconvenience.