BrightTax now supports creating and submitting Corporation Tax returns for accounting periods ending up to 31 March 2027. This article summarises the key changes introduced for the 2026 period and explains how they are handled in BrightTax.

The 2026 update introduces HMRC's updated CT 2026 form and taxonomy, along with three specific changes that affect how certain fields and calculations work. CT rates and marginal relief thresholds remain unchanged from 2025.

For accounting periods that are less than 12 months in length, the R&D PAYE cap on CT600L is now calculated on a time-apportioned basis rather than the previous fixed £20,000 amount.

For example, for a nine-month accounting period, the cap would be calculated as 9/12 of the annual threshold. BrightTax performs this calculation automatically — you do not need to manually apportion the figure.

CT600E Box 195 now supports up to 12 entries for the 2026 period. If you have previously been unable to record all required entries due to the previous entry limit, you can now do so within BrightTax for 2026 returns.

There is no action required from you to enable this — BrightTax automatically applies the expanded entry limit for accounting periods covered by the 2026 form.

Enterprise Zone capital allowances on CT600 are no longer applicable for accounting periods starting on or after 1 April 2024. BrightTax reflects this by removing the Enterprise Zone capital allowances field for any return where the accounting period start date falls on or after 1 April 2024.

The Corporation Tax rates and marginal relief thresholds for 2026 remain the same as 2025:

• Small profits rate: 19% (profits up to £50,000)
• Main rate: 25% (profits over £250,000)
• Marginal relief: applies to profits between £50,000 and £250,000
• Marginal relief thresholds are divided by the number of associated companies, as in 2025

I cannot see the CT 2026 form — my return is showing the old form

• Check the accounting period end date on the CT return. The CT 2026 form applies to accounting periods ending up to 31 March 2027. If the period end date is before this range, the previous form will apply.
• If the accounting period end date appears correct but the form is still showing as 2025, contact support.

The R&D PAYE cap figure looks different to what I calculated manually

• For short or long accounting periods, the cap is now time-apportioned. BrightTax calculates this automatically. Check the accounting period length to confirm the apportionment is being applied correctly.

Enterprise Zone capital allowances field is missing from my CT600

• This is expected behaviour for accounting periods starting on or after 1 April 2024. Enterprise Zone allowances are no longer applicable for these periods. If you believe the field should be present for your specific period, review the accounting period start date on the return.

Q: Do I need to do anything to enable CT 2026 support in BrightTax?

A: No. BrightTax automatically applies the correct CT form and taxonomy based on the accounting period end date. There are no settings to change.

Q: Are CT rates changing for 2026?

A: No. CT rates and marginal relief thresholds remain unchanged from 2025.

Q: How do I know if a return is using the CT 2026 form?

A: The CT return header in BrightTax will indicate the form year. You can also check the accounting period dates — the CT 2026 form applies to periods ending up to 31 March 2027.

Q: What if my client has an accounting period that started before April 2024 but ends after it?

A: For straddle periods, consult current HMRC guidance on Enterprise Zone allowances. BrightTax applies the rules based on the accounting period start date. Contact support if you need specific guidance on a straddle period scenario.