Corporation Tax Marginal Rate Calculator
Calculate your effective corporation tax rate including marginal relief for profits between £50,000 and £250,000
Comprehensive Guide to Corporation Tax Marginal Rates (2024)
The corporation tax marginal rate system in the UK was introduced in April 2023 to create a smoother transition between the small profits rate (19%) and the main rate (25%). This guide explains how marginal relief works, who qualifies, and how to calculate your effective corporation tax rate.
1. Understanding the Corporation Tax Rate Structure
Since April 2023, the UK has operated a three-tier corporation tax system:
- Small Profits Rate (19%): For companies with profits up to £50,000
- Main Rate (25%): For companies with profits over £250,000
- Marginal Rate: For companies with profits between £50,000 and £250,000, where the 25% rate applies but marginal relief reduces the effective rate
The thresholds are reduced proportionally for:
- Short accounting periods (less than 12 months)
- Companies with associated companies (divided by 1 + number of associates)
2. How Marginal Relief Works
Marginal relief provides a gradual increase in the effective tax rate for profits between the lower and upper limits. The formula for calculating marginal relief is:
Where:
- Upper Limit = £250,000 (adjusted for accounting period and associated companies)
- Main Rate = 25%
- Small Profits Rate = 19%
3. Step-by-Step Calculation Process
- Determine your accounting period: Standard is 12 months, but shorter periods adjust the thresholds proportionally
- Count associated companies: Includes companies under common control or significant influence
- Calculate adjusted thresholds:
- Lower limit = £50,000 / (1 + number of associates) × (accounting period/12)
- Upper limit = £250,000 / (1 + number of associates) × (accounting period/12)
- Apply the appropriate rate:
- Profits ≤ lower limit: 19% (small profits rate)
- Profits ≥ upper limit: 25% (main rate)
- Profits between limits: 25% minus marginal relief
4. Practical Examples
| Scenario | Taxable Profits | Associated Companies | Effective Tax Rate | Tax Due |
|---|---|---|---|---|
| Small business | £40,000 | 0 | 19% | £7,600 |
| Medium business | £120,000 | 0 | 22.5% | £27,000 |
| Large business | £300,000 | 0 | 25% | £75,000 |
| Group company | £120,000 | 2 | 24.3% | £29,160 |
5. Common Mistakes to Avoid
- Ignoring associated companies: Forgetting to count associated companies can lead to incorrect threshold calculations
- Incorrect accounting periods: Not adjusting for short accounting periods results in wrong threshold amounts
- Misapplying marginal relief: Calculating relief based on unadjusted thresholds rather than the adjusted amounts
- Overlooking taxable adjustments: Using accounting profit instead of taxable profit (after additions and deductions)
- Missing deadlines: Corporation tax is due 9 months and 1 day after the accounting period ends
6. Planning Opportunities
Understanding the marginal rate system creates several planning opportunities:
- Profit extraction timing: Deferring or accelerating income to manage which rate applies
- Group structuring: Organizing associated companies to optimize threshold allocations
- Loss utilization: Using brought-forward losses to reduce taxable profits into lower brackets
- Capital allowances: Maximizing claims to reduce taxable profits
- R&D tax credits: Increasing the super-deduction to reduce taxable profits
| Strategy | Taxable Profits | Effective Rate | Tax Saved |
|---|---|---|---|
| No planning | £150,000 | 23.75% | £0 |
| £20k capital allowances | £130,000 | 23.08% | £1,015 |
| £30k R&D super-deduction | £120,000 | 22.50% | £2,175 |
| Profit split between 2 companies | £75,000 each | 21.25% avg | £3,750 |
7. Recent Changes and Future Outlook
The current system was introduced in the 2021 Budget and took effect from April 2023, replacing the previous single-rate system (19% for all companies). Key changes included:
- Introduction of the 25% main rate (first increase since 1974)
- Creation of the marginal relief system to smooth the transition
- Adjustment of thresholds for associated companies and short accounting periods
- Maintenance of the 19% small profits rate for the smallest businesses
Looking ahead, there are no announced changes to the corporation tax rates or thresholds for the 2024/25 tax year. However, businesses should monitor:
- Potential adjustments to the small profits rate in future Budgets
- Changes to capital allowances that affect taxable profits
- Possible reforms to the associated company rules
- Developments in international tax rules affecting UK multinational companies
8. How to Pay Your Corporation Tax
Once you’ve calculated your corporation tax liability using this calculator, you’ll need to:
- File your Company Tax Return (CT600) with HMRC within 12 months of your accounting period end
- Pay the corporation tax due within 9 months and 1 day of your accounting period end
- Keep records for at least 6 years from the end of the accounting period
Payment can be made:
- Online via the HMRC website (recommended)
- By telephone banking (Faster Payments)
- By CHAPS or Bacs transfer
- At your bank or building society
9. Frequently Asked Questions
Q: What counts as an associated company?
A: An associated company is any company under the control of the same person or group of people, or where one company controls another. This includes:
- Subsidiary companies
- Sister companies under common control
- Companies where the same person has significant influence (typically >50% ownership)
Q: How do I know if I qualify for the small profits rate?
A: You qualify for the 19% small profits rate if your taxable profits are:
- £50,000 or less (for a 12-month period with no associated companies)
- Adjusted for your accounting period length and number of associated companies
Q: Can I reduce my corporation tax bill?
A: Yes, common ways to legitimately reduce your corporation tax include:
- Claiming capital allowances on equipment and machinery
- Utilizing R&D tax credits for qualifying activities
- Carrying forward trading losses from previous years
- Making pension contributions
- Donating to charity (though this reduces profits rather than giving direct tax relief)
Q: What happens if I pay my corporation tax late?
A: HMRC charges interest on late payments at:
- Current rate: 7.75% (from 22 August 2023)
- Calculated daily from the due date until payment
- No penalties for first late payment, but interest applies immediately
Q: Do I need to pay corporation tax on my first year’s profits?
A: Yes, but you have more time to pay for your first accounting period. The payment deadline is:
- 9 months and 1 day after the end of your first accounting period
- This is often longer than 9 months from incorporation if your first period is longer than 12 months
10. When to Seek Professional Advice
While this calculator provides accurate estimates, you should consult a tax professional if:
- Your company has complex group structures with multiple associated companies
- You have international operations or overseas subsidiaries
- Your accounting period is not 12 months or spans tax year changes
- You’re considering significant profit extraction or restructuring
- You’re claiming substantial R&D tax credits or capital allowances
- You’ve received a tax enquiry from HMRC
A qualified accountant or tax advisor can:
- Verify your calculations and ensure compliance
- Identify additional tax reliefs you may qualify for
- Help with optimal profit extraction strategies
- Assist with HMRC enquiries or disputes
- Provide year-round tax planning advice