What Is Corporation Tax and Why Should Agency Founders Care?
Corporation tax is the tax your limited company pays on its profits. If you run your agency as a sole trader or partnership, you pay income tax and National Insurance instead. But if you've incorporated, and most agency founders do once they pass £50k-£80k turnover, then corporation tax is your company's direct tax bill.
For the 2025/26 tax year, the rates are straightforward at the top level but the details matter. Get them wrong and you overpay. Get them right and you keep more of what your agency earns.
This guide covers everything a UK agency founder needs to know about corporation tax agency compliance: the rates, the deadlines, the reliefs, and the specific traps that catch agency businesses.
Corporation Tax Rates for 2025/26
There are three effective rates depending on your agency's profit level. Here is how they work.
Small Profits Rate: 19%
If your agency's annual profits are £50,000 or less, you pay 19% on all of them. This is the rate most agency founders with 1-5 person teams will pay. A 12-person digital agency billing £800k per year with £120k profit would pay £22,800 in corporation tax at this rate.
Main Rate: 25%
If your agency's profits exceed £250,000, you pay 25% on all profits. This affects larger agencies. A 30-person creative agency turning over £3.2m with £400k profit would owe £100,000 in corporation tax.
Marginal Relief: Between £50k and £250k
Between £50k and £250k of profit, you get marginal relief. This means your effective rate sits somewhere between 19% and 25%, rising as profits increase. The calculation is formula-based, and your accounting software or accountant will handle it.
For a typical agency making £85,000 profit, the effective rate is roughly 21-22%. Not 19% and not 25%. The exact figure depends on the marginal relief calculation.
Corporation Tax Deadlines Every Agency Founder Must Know
Miss these and HMRC charges interest and penalties. Here are the key dates.
Payment Deadline
Corporation tax is due 9 months and 1 day after your company's accounting period ends. If your year-end is 31 March 2026, payment is due by 1 January 2027. If your year-end is 30 June 2025, payment is due by 1 April 2026.
This is a hard deadline. HMRC does not send reminders. Set a calendar alert now.
Filing Deadline
Your company's corporation tax return (form CT600) must be filed within 12 months of the accounting period end. For a 31 March 2026 year-end, the filing deadline is 31 March 2027.
File late and you face an automatic penalty: £100 for one day late, then more. After 6 months, HMRC adds a further penalty of 10% of the unpaid tax. After 12 months, another 10%.
Quarterly Instalment Payments (for Large Agencies)
If your agency's profits exceed £1.5m, you must pay corporation tax in quarterly instalments. Most agency founders reading this will not hit that threshold. But if you are scaling fast, keep it in mind. Your accountant will flag it when it applies.
What Counts as a Deductible Expense for Your Agency?
Corporation tax is calculated on your agency's taxable profits. That is turnover minus allowable expenses. The lower your taxable profit, the less tax you pay. But only certain expenses count.
Fully Deductible
- Staff salaries and bonuses, including your own director's salary up to the personal allowance (£12,570 for 2025/26)
- Employer's National Insurance, 15% on salaries above the secondary threshold
- Rent and business rates, for your agency's office or co-working space
- Software subscriptions, Xero, QuickBooks, FreeAgent, Dext, Float, Spotlight Reporting, project management tools, design software, CRM platforms
- Professional fees, accountancy, legal, consultancy
- Marketing and advertising, Google Ads, LinkedIn Ads, PR retainers, content production
- Travel and subsistence, client meetings, industry events, but not ordinary commuting
- Equipment and technology, laptops, monitors, cameras, servers (subject to capital allowances)
- Training and development, courses, conferences, professional memberships
- Insurances, professional indemnity, public liability, cyber insurance
Partially Deductible or Restricted
- Client entertaining, 100% disallowable for corporation tax purposes. You cannot deduct the cost of taking clients to lunch or events. Staff entertaining (like the Christmas party) is deductible up to £150 per head per year.
- Directors' loan account interest, if you borrow from the company, the benefit is taxable on you personally, not the company.
- Subscriptions to non-trade bodies, check with your accountant.
Not Deductible
- Dividends paid to shareholders, these are a distribution of profit, not a cost. You pay corporation tax on the profit before dividends.
- Capital expenditure on buildings, separate rules apply.
- Fines and penalties, including late filing penalties.
- Personal expenses, anything not wholly and exclusively for the business.
Capital Allowances: Claiming for Agency Equipment
When your agency buys equipment, laptops, monitors, cameras, office furniture, servers, you do not deduct the full cost as an expense in one go. Instead, you claim capital allowances.
The Annual Investment Allowance (AIA) lets you deduct 100% of the cost of most plant and machinery in the year you buy it, up to £1m per year. For a typical agency spending £15,000 on new laptops and monitors, that is a full deduction against profits.
If you buy a van for client site visits or a camera for content production, the same applies. Keep receipts and records.
R&D Tax Credits for Agencies
Many agency founders assume R&D tax credits are only for pharmaceutical or engineering companies. That is wrong. Software agencies, digital agencies, AI agencies, and creative agencies developing new tools, algorithms, or processes can qualify.
For accounting periods beginning on or after 1 April 2024, the merged R&D scheme applies: a single 20% taxable expenditure credit on qualifying spend, giving a net benefit of approximately 15% after corporation tax. The old SME enhanced deduction of 186% applied only to periods beginning before 1 April 2024. If your agency spent £50,000 on qualifying R&D in a post-March-2024 period, the 20% credit gives roughly £7,500 net benefit after tax.
Common qualifying activities in agencies include: building proprietary software tools, developing AI-driven analytics platforms, creating new automation processes, and designing novel campaign measurement systems.
If you think your agency might qualify, ask your accountant before year-end. Claims must be made within two years of the end of the accounting period.
Directors' Loan Account: The Trap That Costs You
If your agency lends you money as a director, that creates a directors' loan account balance. If the loan is over £10,000 or not repaid within 9 months of your year-end, the company faces a Section 455 tax charge at 35.75% of the outstanding amount.
This is not a penalty. It is a tax charge that gets refunded when you repay the loan. But it ties up cash in HMRC's hands for months or years. Avoid it by keeping loan accounts in credit or repaying within the 9-month window.
A common scenario: a founder takes a £20,000 draw from the company in November 2024, with a March 2025 year-end. If that £20,000 is still outstanding on 1 January 2026 (9 months after year-end), the company owes £6,750 in S455 tax. That is cash you could have used for growth.
How to Pay Corporation Tax
Payment is made to HMRC via your company's online account. You can pay by:
- Direct debit (set up in advance)
- Bank transfer (Faster Payments, CHAPS, or Bacs)
- Debit or credit card (fees apply)
- Corporate credit card
Set up a direct debit if you can. It avoids missed deadlines and the associated penalties. Your accountant can help set this up when they file the CT600.
What Happens If You Miss a Deadline?
HMRC charges interest on late payments at the Bank of England base rate plus 2.5%. As of early 2025, that is around 7.75% annual interest on overdue corporation tax. Penalties start at £100 for a late CT600 and escalate.
If you know you will miss a deadline, tell your accountant immediately. They can often agree a Time to Pay arrangement with HMRC, spreading the tax bill over 6-12 months. But this must be arranged before the deadline, not after.
Corporation Tax Planning Before Year-End
Do not wait until after year-end to think about corporation tax. Here are three actions to take before your accounting period ends.
1. Review Your Profit Level
If your profit is heading toward £50k or £250k, the marginal relief calculation changes your effective rate. A small adjustment, buying equipment before year-end, paying a bonus, could save thousands.
2. Claim All Allowable Expenses
Go through your bank statements with your accountant. Missing expenses like software subscriptions, professional memberships, and travel costs leaves money on the table.
3. Check Your Directors' Loan Account
If you have borrowed from the company, repay before the 9-month window closes. Or convert the loan to a formal dividend if there are sufficient retained profits.
Working With a Specialist Agency Accountant
Corporation tax is not complicated in principle, but the details matter. Rates, reliefs, deadlines, and traps vary by agency type, profit level, and structure. A specialist accountant who works with agency founders will spot opportunities a general practitioner might miss.
At Agency Founder Finance, we work exclusively with agency founders. We handle your corporation tax compliance, year-end filing, and planning so you can focus on building your agency. See our services here or get in touch.
We work with marketing agencies, digital agencies, creative agencies, advertising agencies, PR agencies, web design agencies, SEO agencies, recruitment agencies, and more. If you run an agency, we understand your numbers.
For more on related topics, read our guides on salary and dividends for agency founders, incorporation and structure, and growth and exit planning.
Final Takeaway
Corporation tax for agency founders in 2025/26 is manageable if you know the rates, the deadlines, and the reliefs. Pay on time, claim what you are entitled to, and plan before year-end. Your accountant should make this straightforward, not stressful.
If your contractor mix has changed in the last 12 months, or you are approaching the £50k or £250k profit thresholds, ask your accountant before year-end. A few hours of planning now can save thousands in tax later.
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