Annual Investment Allowance Explained
The Annual Investment Allowance (AIA) is a capital allowance that enables businesses to deduct 100% of the cost of qualifying plant and machinery from their taxable profits in the year of purchase. It provides immediate tax relief on capital expenditure, rather than spreading the relief over several years through writing down allowances.
The AIA is available to all businesses — sole traders, partnerships, and limited companies — and applies against income tax or corporation tax as applicable.
The Current AIA Limit
The AIA limit is permanently set at £1,000,000 per year. This means businesses can deduct up to £1 million of qualifying capital expenditure in full against their taxable profits each year.
The £1 million limit was made permanent from April 2023. Before that, the limit changed frequently, which is why older accounting periods sometimes needed the straddling calculations described below.
For most small and medium businesses, the £1 million limit is more than sufficient to cover annual capital expenditure in full.
What Qualifies for AIA?
The AIA applies to expenditure on plant and machinery, which broadly covers items used in the business. Qualifying assets include:
General Plant and Machinery
- Computers, laptops, and IT equipment
- Office furniture and fittings
- Tools and equipment
- Manufacturing machinery
- Commercial vehicles (vans, lorries, but not cars)
- Agricultural machinery
- Catering and kitchen equipment
Integral Features
Certain building-related items classified as integral features also qualify for AIA:
- Electrical systems (including lighting)
- Heating, ventilation, and air conditioning systems
- Cold water systems
- Lifts and escalators
- External solar shading
Fixtures in Buildings
Items that become fixed to a building may qualify, including:
- Fire alarm and sprinkler systems
- Kitchen and bathroom fittings in commercial properties
- Security systems
- Fitted carpets and floor coverings
What Does Not Qualify?
The AIA cannot be claimed on:
- Cars — these have their own capital allowance rules (but vans do qualify)
- Land and buildings — these are not plant and machinery
- Items given to the business — only purchased items qualify
- Items bought before the business started trading
- Leased assets — where the business is the lessee under an operating lease
Cars
Cars are excluded from AIA but qualify for other capital allowances:
| CO2 Emissions | Capital allowance treatment |
|---|---|
| 0 g/km (fully electric) | 100% first-year allowance while the relief is available |
| Up to 50 g/km | Main rate pool |
| Over 50 g/km | Special rate pool |
HMRC publishes the current writing down percentages for each pool and the end date of the first-year allowance for zero-emission cars.
How to Claim AIA
For Sole Traders and Partnerships
AIA is claimed on the capital allowances section of the self-assessment tax return. The expenditure reduces your taxable trading profit, which in turn reduces your income tax and National Insurance liability.
For Limited Companies
AIA is claimed on the CT600 corporation tax return. The expenditure reduces the company’s taxable profits, saving corporation tax at the applicable rate.
Tax Saving Calculation
The tax saving from AIA depends on your tax rate:
| Business Type | Tax Rate | Saving per £10,000 AIA |
|---|---|---|
| Basic rate sole trader | 20% | £2,000 |
| Higher rate sole trader | 40% | £4,000 |
| Small profits company | 19% | £1,900 |
| Main rate company | 25% | £2,500 |
AIA and Accounting Periods
The AIA limit of £1 million relates to a 12-month period. If your accounting period is shorter or longer than 12 months, the AIA limit is proportionally adjusted.
For example, if a company has a 9-month accounting period, the AIA limit is:
£1,000,000 x 9/12 = £750,000
Straddling Periods
When the AIA limit changes and your accounting period straddles the change date, the calculation becomes more complex. The period is split at the change date, and each part gets a proportionate share of the relevant limit.
Expenditure Exceeding the AIA Limit
If capital expenditure exceeds £1 million, the excess is allocated to the appropriate writing down allowance (WDA) pool:
| Pool | Rate | Assets |
|---|---|---|
| Main rate pool | Main rate set by Parliament | Most plant and machinery |
| Special rate pool | 6% per year | Integral features, long-life assets, thermal insulation |
The WDA is calculated on a reducing balance basis. So the allowance each year is applied to the remaining pool balance, not the original cost.
AIA and Full Expensing
Since April 2023, companies (not sole traders or partnerships) can also claim full expensing — a 100% first-year allowance on qualifying main rate plant and machinery with no upper limit. This means:
| Relief | Available To | Limit | Assets |
|---|---|---|---|
| AIA | All businesses | £1 million | All qualifying P&M |
| Full expensing | Companies only | No limit | Main rate P&M only |
| 50% first-year allowance | Companies only | No limit | Special rate P&M only |
For companies with expenditure above £1 million, full expensing provides unlimited 100% relief on main rate assets. The AIA remains important for:
- Sole traders and partnerships who cannot claim full expensing
- Special rate assets (integral features) where full expensing only gives 50%
Practical Considerations
Timing of Purchases
AIA is claimed in the accounting period when the expenditure is incurred. This is normally when the obligation to pay becomes unconditional, not when the asset is delivered or paid for.
For hire purchase, the full cost (excluding interest) qualifies for AIA at the time the contract is entered into.
Groups and Related Businesses
The AIA is shared between associated businesses and group companies. If two businesses are under common control, they share a single AIA of £1 million between them, not £1 million each.
Groups can allocate the AIA between group companies in any proportion they choose, but the total cannot exceed £1 million.
Record Keeping
You must keep records of all capital expenditure to support your AIA claims, including:
- Purchase invoices
- Proof of payment
- Details of assets acquired and disposed of
- Evidence of business use
These records should be retained for at least 5 years (sole traders) or 6 years (companies) as part of your general accounting records. Under Making Tax Digital, capital allowance records must be maintained digitally.
Disposing of AIA Assets
When you sell or dispose of an asset that was claimed under AIA, the sale proceeds create a balancing charge that is added back to taxable profits. This effectively claws back the tax relief on the amount received.
If the proceeds exceed the original cost (rare for depreciating assets), the excess is also taxable.
Example
| Item | Amount |
|---|---|
| Original cost of equipment | £50,000 |
| AIA claimed | £50,000 |
| Equipment sold 3 years later for | £15,000 |
| Balancing charge (added to profits) | £15,000 |
The balancing charge means you have received net tax relief only on the actual depreciation of the asset (£35,000 in this example), which is the economically correct outcome.
AIA and Other Tax-Deductible Costs
It is important to distinguish between revenue expenses and capital expenditure. Day-to-day running costs are claimed as tax-deductible expenses and reduce taxable profits directly. Capital expenditure on lasting assets is claimed through the AIA or writing down allowances.
Repairs and maintenance of existing assets are revenue expenses — but improvements and replacements with superior items are capital expenditure qualifying for AIA.