Corporation Tax is one of those subjects that looks simple from a distance and becomes much more technical the moment a company starts making real profit. For UK limited companies, that matters more now than it did a few years ago. Since April 2023, the old single-rate system has been replaced by a three-part structure: 19% for smaller profits, 25% for larger profits, and Marginal Relief in between. At the same time, HMRC’s own statistics show how significant company tax now is to the public finances: total corporate tax receipts reached £97.2 billion in 2024–25, with onshore Corporation Tax receipts up to £89.2 billion.
This is also an area where mistakes are costly. HMRC estimates the overall Corporation Tax gap at 15.8% for 2023–24, equivalent to £18.6 billion, and for small businesses the Corporation Tax gap is far higher at 40.1%. That helps explain why getting the basics right, from expense classification to deadlines, is not just admin hygiene but risk management.
What Corporation Tax actually is and when a limited company becomes liable
Corporation Tax is charged on the profits a company makes during its accounting period. For a UK resident company, taxable profits can include trading profits, investment income, and chargeable gains on assets sold for more than they cost. Unlike personal tax, HMRC does not usually send a bill telling the company what to pay. The company has to work out, report, and pay the tax itself.
A new limited company also needs to recognise when it becomes “active” for Corporation Tax. HMRC says you must tell them within 3 months of starting your tax accounting period if the company is within the charge to Corporation Tax and is now active. In practice, that usually means once the company starts trading, provides services, earns interest, or receives other income.That point is easy to miss with newly incorporated businesses. Many directors assume incorporation automatically handles everything. Sometimes it does not. A company can also be dormant for Corporation Tax between incorporation and the date it actually starts trading, which is why the start date matters so much for registration, deadlines, and first-year filings.
Current Corporation Tax rates for 2024 to 2026
For non-ring-fence profits, HMRC’s published rates are unchanged across 2024, 2025, and 2026. Companies with profits under £50,000 pay the small profits rate of 19%. Companies with profits over £250,000 pay the main rate of 25%. Companies between those limits may claim Marginal Relief, which gradually increases the effective rate between the two bands.
That middle band is where many owner-managed companies underestimate their tax exposure. Once profits move above £50,000, the company is no longer simply in a “19% world.” For a straightforward standalone company, the Marginal Relief taper means each extra £1 of taxable profit in that band effectively faces a 26.5% marginal rate before other reliefs. That is one reason timing capital expenditure, pension contributions, bonuses, and other deductible costs can make a meaningful difference around year-end. This 26.5% figure is an inference from HMRC’s current 19%/25% bands and Marginal Relief fraction.
A simple example shows how the band works. If a standalone company has taxable profits of £40,000, its Corporation Tax is £7,600 at 19%. If taxable profits are £100,000, the company falls into the Marginal Relief band and the tax works out at about £22,750, giving an effective rate of 22.75%. If profits reach £300,000, the company is above the upper limit and pays the full 25%, or £75,000. These calculations use HMRC’s current published thresholds and Marginal Relief rules.
Why associated companies can change the answer
One of the most overlooked rules is that the £50,000 and £250,000 thresholds are not always the thresholds you actually get. HMRC says these limits are reduced for short accounting periods and also reduced by the number of associated companies. Its own example shows that if a company has 3 associated companies, the lower limit becomes £12,500 and the upper limit becomes £62,500.
That means a group structure can pull a business into higher-rate territory much earlier than the directors expect. A company that looks “small” on a standalone profit number can still lose access to the 19% rate band more quickly once the associated company rule is applied.
How taxable profits are really worked out
Corporation Tax is charged on taxable profit, not turnover and not accounting profit without adjustment. HMRC says the trading profit or loss for Corporation Tax purposes is worked out by making the usual tax adjustments to the profit or loss shown in the company’s financial accounts.
That is where many practical issues begin. Some costs are deductible as revenue expenses, but capital spending is generally dealt with through capital allowances instead. HMRC’s current guidance says revenue expenses can be fully deducted only if they are not specifically disallowed and they are incurred wholly and exclusively for the business. It specifically flags client entertaining as an example of something disallowed.
The distinction between revenue and capital is not just technical bookkeeping. It affects timing. A deductible running cost reduces taxable profit immediately. A capital purchase may still reduce the bill, but only through allowances or first-year reliefs. HMRC also warns that anything directors or employees get personal use from must be treated as a benefit, so trying to push mixed-use spending through the company without proper treatment can create problems beyond Corporation Tax alone.
Reliefs and deductions that move the tax bill in practice
For most limited companies, the biggest planning gains come from using the right relief at the right time rather than hunting for obscure loopholes.
- Revenue expenses can reduce taxable profit if they are genuine running costs, not specifically disallowed, and satisfy the wholly-and-exclusively business test.
- Annual Investment Allowance (AIA) lets a business deduct the full value of qualifying plant and machinery up to £1 million in an accounting period.
- Full expensing allows companies to deduct 100% of the cost of qualifying new and unused plant and machinery bought from 1 April 2023, while the 50% first-year allowance applies to certain special rate assets. Cars are excluded.
- R&D relief changed from 1 April 2024. For accounting periods beginning on or after that date, the old SME and RDEC schemes are replaced by the merged RDEC scheme and ERIS for qualifying loss-making R&D-intensive SMEs. HMRC says ERIS can produce a total deduction of 186% of qualifying costs and a payable credit worth up to 14.5% of the surrenderable loss.
- Charitable giving through the company can also reduce Corporation Tax, because the value of qualifying donations can be deducted from total business profits before tax.
- Loss relief still matters, but it is no longer a simple “wipe out all future profit” tool for bigger profit-makers. HMRC says carried-forward losses are subject, broadly, to a £5 million allowance plus 50% of remaining profits above that amount for periods from 1 April 2017.
A very current 2026 point is capital allowances. Budget 2025 measures introduced a new permanent 40% first-year allowance for certain assets from 1 January 2026, while the main rate writing-down allowance drops from 18% to 14% from 1 April 2026 for Corporation Tax. In other words, the direction of travel is clear: the tax system is rewarding upfront qualifying investment more heavily, while making slower pool relief slightly less generous.
Deadlines every limited company director should know
Directors often confuse three separate obligations: Companies House accounts, Corporation Tax payment, and the Company Tax Return. They are related, but they are not the same deadline. HMRC and GOV.UK currently set them out as follows:
- Tell HMRC the company is active: within 3 months of starting the tax accounting period or becoming active.
- Pay Corporation Tax: usually 9 months and 1 day after the end of the accounting period.
- File the Company Tax Return: 12 months after the end of the accounting period.
- File annual accounts at Companies House: usually 9 months after the company’s financial year end.
The first year can be especially awkward. GOV.UK notes that a Corporation Tax accounting period cannot be longer than 12 months, so if your first accounts cover more than 12 months, you may need to file 2 Corporation Tax returns and deal with 2 payment deadlines. That is a common startup trap.
There is also an important 2026 admin change. HMRC says Company Tax Returns must be filed electronically, the computations and accounts must be in iXBRL, and you must use proprietary third-party software. It also notes that the format guidance was updated following the closure of the HMRC online filing service on 31 March 2026. In plain English, software-based filing is now the normal route, not an optional upgrade.
If you discover an error after filing, HMRC says you usually have 12 months from the filing deadline to amend the return. That gives companies a correction window, but it is still better to fix the computation before submission than to rely on post-filing amendments.
When companies have to pay in instalments instead of waiting until year-end
Many directors assume Corporation Tax is always paid after the accounting period ends. That is true for smaller companies, but not for all of them.
HMRC says companies with annual taxable profits above £1.5 million and below £20 million are normally large companies for instalment purposes. For a 12-month accounting period, they usually pay in 4 instalments, with the first due 6 months and 13 days after the first day of the accounting period, then every 3 months after that. The thresholds are also reduced by associated companies.
Very large companies, with profits above £20 million at an annual rate, pay even earlier. HMRC says a 12-month accounting period requires 4 instalments due on the 14th day of months 3, 6, 9 and 12 of the accounting period, again with threshold reduction for associated companies.
This matters because cash flow planning changes completely once instalments apply. A business can be profitable on paper and still run into stress if it budgets for tax after year-end but is actually required to prepay during the year.
The 2026 compliance trend directors should not ignore
The direction of travel in 2026 is tighter administration, not looser administration. The tax rates themselves are stable through financial year 2026, but filing and compliance are becoming stricter. HMRC’s November 2025 measure says that for Corporation Tax returns with a filing date on or after 1 April 2026, fixed late-filing penalties rise from £100 to £200 and from £200 to £400 once the return is more than 3 months late. Repeat-failure penalties also double, from £500 to £1,000 and from £1,000 to £2,000.
That change is bigger than it looks. It means late filing is no longer a small nuisance cost for companies that habitually miss deadlines. Combined with software-only filing and HMRC’s continued focus on the tax gap, the message is clear: Corporation Tax is becoming more digitised and less forgiving.
What good Corporation Tax management looks like in a small or mid-sized company
For most limited companies, good Corporation Tax management is not about aggressive tax planning. It is about building a disciplined process.
A well-run company usually does four things consistently. It keeps bookkeeping current enough that taxable profit is visible before year-end. It separates revenue spending from capital spending early, instead of cleaning the classification up months later. It reviews profit levels before the year closes, especially around the £50,000 and £250,000 Marginal Relief thresholds. And it treats filing as a software-supported compliance task, not a last-week scramble. Those habits align with HMRC’s current rules on electronic filing, iXBRL, deductible expenses, capital allowances, and rate bands.
For director-owned businesses, one more point matters: Corporation Tax should not be planned in isolation. Salary, employer pension contributions, dividends, asset purchases, charitable giving, and R&D claims all change the final number. The best decisions usually come from looking at the full profit extraction and investment picture rather than asking, at the end of the year, “What is the tax bill?”
Conclusion
Corporation Tax for UK limited companies is no longer a simple flat-percentage exercise. The current system is more layered: 19% for smaller profits, 25% for larger profits, Marginal Relief in between, associated-company adjustments, more detailed capital allowance choices, reworked R&D relief, software-led filing, and tougher late-filing penalties from April 2026.
The practical takeaway is straightforward. The companies that manage Corporation Tax well are not necessarily the ones using exotic structures. They are usually the ones that understand their thresholds, claim the reliefs they are genuinely entitled to, keep clean records, and plan before the accounting period ends instead of after the deadline has passed. With rates stable but compliance tightening, that approach is likely to matter even more over the next few years.
FAQs
What is Corporation Tax for a UK limited company?
Corporation Tax is the tax a UK limited company pays on its taxable profits, including trading profits, investment income, and chargeable gains.
What is the current Corporation Tax rate in the UK?
The current rates are 19% for profits up to £50,000, 25% for profits over £250,000, and Marginal Relief may apply in between.
When does a limited company have to pay Corporation Tax?
Most companies must pay Corporation Tax 9 months and 1 day after the end of their accounting period.
When is the Company Tax Return due?
The Company Tax Return is usually due 12 months after the end of the accounting period.
Do all limited companies pay the same rate of Corporation Tax?
No, the rate depends on the level of taxable profits and whether Marginal Relief applies.
What expenses can reduce a Corporation Tax bill?
Allowable business expenses, qualifying capital allowances, charitable donations, and some R&D costs can reduce taxable profits.
What is Marginal Relief?
Marginal Relief helps reduce the Corporation Tax bill for companies with profits between £50,000 and £250,000.
Can associated companies affect Corporation Tax thresholds?
Yes, if a company has associated companies, the profit thresholds for the tax bands are divided, which can increase the effective tax rate sooner.
Do companies need software to file Corporation Tax returns?
Yes, Corporation Tax returns must now be filed digitally using compatible software with accounts and computations in the correct format.
What happens if a company files its Corporation Tax return late?
Late filing can lead to penalties, and from April 2026 the fixed penalties for late Corporation Tax returns have increased.