Key facts
- Disallowable expenses are costs included in your accounts that are not deductible for Corporation Tax.
- They must be added back in the tax computation to arrive at taxable profit.
- The most common add-backs are depreciation, client entertaining, fines, and capital expenditure.
- Some items are specifically prohibited by legislation; others fail the “wholly and exclusively” test.
Which Expenses Cannot Be Deducted from Corporation Tax
When preparing your company’s statutory accounts, the profit and loss account will include all expenditure — whether or not it is deductible for tax. The tax computation then adjusts this accounting profit by adding back any costs that tax law does not allow as a deduction.[1] CT600 filing software applies these add-backs as part of the computation.
These non-deductible costs fall into two broad categories:
- Specifically prohibited — items that legislation expressly denies (e.g. business entertainment)
- Fails the test — items that do not meet the “wholly and exclusively for trade purposes” requirement
Common Disallowable Expenses
The table below lists the most frequently encountered add-backs in a company’s Corporation Tax computation:
| Expense | Why It’s Disallowable | Tax Treatment |
|---|---|---|
| Depreciation & amortisation | Accounting estimates, not recognised for tax | Add back; claim capital allowances instead[4] |
| Client entertaining | Specifically prohibited by legislation | Always add back — no exceptions[2] |
| Fines and penalties | Arising from breaking the law (parking tickets, HMRC penalties, court fines) | Add back in full[1] |
| Political donations | Specifically prohibited; not a trade expense | Add back in full |
| Capital expenditure | Purchase or improvement of long-term assets | Add back; claim capital allowances or SBA[4] |
| General provisions | Not specific enough for tax — only specific bad debts qualify | Add back; deduct only when debts are specifically identified and written off |
| Donations to non-qualifying bodies | Only Gift Aid donations to registered charities are deductible | Add back unless paid under Gift Aid |
| Personal expenses of directors/shareholders | Fail the “wholly and exclusively” test | Add back; may also trigger BIK or s.455 charge |
| Legal costs for capital transactions | Legal fees on acquiring/disposing of assets are capital in nature | Add back; may form part of the base cost for chargeable gains |
| Impairment losses on non-trade assets | Not related to the company’s trade | Add back; dealt with under separate tax rules (e.g. loan relationships) |
Business Entertainment in Detail
Business entertainment is one of the most clear-cut disallowable expenses. It covers hospitality of any kind provided to clients, customers, suppliers, or other business contacts.[2]
This includes:
- Restaurant meals with clients
- Tickets to sporting events, theatre, or concerts
- Corporate hospitality days
- Gifts to customers (unless small branded items under £50 per person per year that are not food, drink, or tobacco)
Staff entertainment is different: Reasonable entertainment for employees (e.g. a Christmas party costing up to £150 per head) is allowable for Corporation Tax, provided it is genuinely for staff and not a disguised client event.[2]
Depreciation & Capital Expenditure
Accounting depreciation and amortisation are always added back because they are subjective estimates. Tax law replaces them with capital allowances, which are calculated using prescribed rates and rules.[4]
Common examples of capital expenditure that must be added back include:
- Purchase of plant, machinery, and equipment
- Computer hardware and servers
- Vehicles
- Improvements to existing assets (as distinct from repairs)
- Costs of acquiring intangible assets (goodwill, patents, trademarks)
Remember: Although these costs are added back as expenses, relief is normally available through capital allowances, Structures & Buildings Allowance, or the intangible fixed assets regime.
Grey Areas & Dual-Purpose Expenses
Some expenses have both a business and a personal element. Where the two elements can be separately identified, HMRC may accept an apportionment — but only the business portion is deductible.[3]
Examples include:
- Mobile phone bills — business calls are allowable; personal calls are not
- Use-of-home costs — a reasonable business proportion may be claimed
- Travel with a personal element — if a business trip is extended for a holiday, only the business days’ costs are allowable
Where a cost is inseparably mixed (e.g. a suit worn for both business meetings and personal occasions), the entire cost is disallowable.
Frequently Asked Questions
What are the most common disallowable expenses for Corporation Tax?
The most common add-backs are depreciation, client entertaining, fines and penalties, political donations, and capital expenditure. These must all be added back in the tax computation.
Is client entertaining deductible for Corporation Tax?
No. Business entertainment of clients, customers, and suppliers is specifically prohibited by legislation and must always be added back. However, staff entertainment (e.g. a Christmas party up to £150 per head) is allowable.
Why is depreciation added back for Corporation Tax?
Depreciation is an accounting estimate and not recognised for tax purposes. It is always added back, and the company claims capital allowances instead using HMRC’s prescribed rates.
Can I deduct a fine from my Corporation Tax?
No. Fines and penalties arising from breaking the law — including parking tickets, HMRC penalties, and court fines — are disallowable and must be added back in full.
Further Reading
- Allowable Business Expenses — the full list of deductible costs for companies
- Taxable Profits Explained — how add-backs fit into the overall tax computation
- Capital Allowances Overview — how to claim relief on capital expenditure
- Benefits in Kind for Directors — when personal expenses trigger a BIK charge
- The CT600 Tax Return — where disallowable expenses feed into the return
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