Corporation Tax & Marginal Relief: Financial Planning for 2026

1. The flat rate is gone

For years, UK Corporation Tax was straightforward to budget for. Whether a company generated £10,000 or £10 million in taxable profit, a single 19% rate applied. The Treasury ended that flat rate in April 2023 to raise revenue while leaving the smallest companies on the old number.

The system is now tiered. The marginal-relief band catches scaling businesses, with an effective rate of 26.5% on profits between £50,000 and £250,000. Running a limited company in 2026 means knowing which profit band the year-end will land in, months before the statutory deadline, so that extraction and capital-spend decisions are timed accordingly.

2. The Three Corporation Tax Tiers

Corporation Tax now falls into one of three bands, depending on your annual taxable profit:

• The Small Profits Rate (19%): companies with taxable profit at or below £50,000 stay on the original 19% rate.
• The Main Rate (25%): companies with taxable profit at or above £250,000 pay the 25% rate across their entire profit pool.
• The Marginal Relief Band (£50,001 to £250,000): companies sitting between the two thresholds pay a blended rate, calculated by HMRC using the Marginal Relief sliding scale.

3. The 26.5% Effective Rate Reality

The most common misunderstanding of the Marginal Relief band is the shape of the taper. When business owners read that the rate slides linearly from 19% to 25%, they often assume the middle of the band equates to a mild 22% rate.

The maths works the other way. The first £50,000 of profit stays at 19%. To bring the whole average up to 25% by the time the company hits £250,000, the profits generated inside the band itself have to be taxed at a higher rate than 25%.

The result is that every additional pound of profit between £50,000 and £250,000 is effectively taxed at 26.5%.

If your company forecasts an end-of-year profit of £75,000, growing that profit to £85,000 means the additional £10,000 is taxed at 26.5%, not 19%. Setting the cashflow provision at 19% on those marginal pounds leaves a shortfall when the Corporation Tax payment lands, nine months and one day after year-end.

4. The associated companies rule

Directors holding multiple corporate entities are caught a second time by the Associated Companies legislation. The £50,000 and £250,000 limits do not apply per company; they are divided by the total number of associated companies under common control.

If a director owns two active limited companies, the thresholds fracture:

• The Small Profits Rate ceiling plummets to £25,000.
• The Main Rate 25% floor drops to just £125,000.

If a business owner operates four separate companies, the Small Profits boundary falls to £12,500 per entity. That pulls micro-businesses into the 26.5% marginal band almost immediately. A holding-company structure or consolidation often becomes the right answer once two or more associated companies are involved.

5. Year-End Profit Mitigation

The 26.5% drag is fixed pre-year-end, not after. The mechanism is to bring taxable profits back down towards the £50,000 floor before the accounting period closes.

The most direct lever is the Employer Pension Contribution. Directing corporate cash straight into a Self-Invested Personal Pension (SIPP) is a fully allowable business expense. On £80,000 of taxable profit, injecting £30,000 into a SIPP does three things at once: it lifts the funds out of the 26.5% Marginal Relief band, returns the company to the 19% Small Profits Rate on what remains, and shelters the contribution inside a tax-advantaged pension wrapper for the director.

6. Research and Development (R&D) Enhancements

For companies investing heavily in custom software, engineering or structural design, the Research and Development (R&D) Tax Relief scheme remains a material lever against Corporation Tax liability.

Recent reforms have merged the historical SME and Research and Development Expenditure Credit (RDEC) schemes into a single harmonised regime. Compliant R&D expenditure generates an enhanced deduction. Even on a profitable company, identifying and segregating qualifying R&D spend (staffing costs, software licences, prototyping materials) can materially reduce taxable profits. Where the R&D deduction takes the company into a tax loss, the loss can often be surrendered to HMRC for a direct cash credit.

7. Capex & Super Deductions

Finally, Capital Expenditure (Capex) timing matters. The Annual Investment Allowance (AIA) permanently lets a company deduct 100% of qualifying plant and machinery, up to £1 million per year, directly against its profits.

If a company is buying significant hardware, fleet vehicles or factory kit, and its forecast profits sit deep inside the Marginal Relief band, bringing that invoice date forward to land three days before the year-end (instead of three days after) gives a 100% deduction in the current period. The deduction can pull the profit position out of the 25% or 26.5% bands altogether. Capital purchase timing is one of the most consequential decisions a director can take in the run-up to year-end.

For implementation support, see our corporation tax service.