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The annual investment allowance lets UK businesses deduct up to £1 million of qualifying capital spend from their taxable profits in the year of purchase. At the main 25% corporation tax rate, that’s a potential tax saving of £250,000 in a single year, which makes AIA one of the most valuable reliefs available to SMEs. If you’ve bought equipment, machinery, vans, or office fit-out this year, you almost certainly qualify.
The rules are simpler than HMRC’s guidance makes them sound, but the costs of missing eligible assets or mis-timing a claim can be significant. This guide walks you through what counts, what doesn’t, and how to claim, with a worked example showing the saving in real numbers. If you’d rather not do this alone, Sleek’s UK accounting services handle capital allowances claims as part of your annual return.
What is the annual investment allowance?
The annual investment allowance is a 100% first-year tax deduction that UK businesses can claim against qualifying capital expenditure on plant and machinery. It allows you to write off the full cost of eligible assets, up to £1 million per accounting period, against your taxable profits in the year you buy them.
AIA is not a cash payment from HMRC. It’s a deduction that reduces the profit figure on which you pay corporation tax in the UK or income tax. The relief was introduced to encourage business investment, and the £1 million limit has been in place since 1 January 2019. The 2024 Autumn Budget confirmed the limit will remain at £1 million permanently, so there is no expiry cliff to plan around.
Who can claim AIA?
Most trading businesses in the UK can claim AIA. The relief applies to:
- Sole traders
- Partnerships made up entirely of individuals
- Limited companies
A few groups are excluded. Trusts cannot claim AIA. Mixed partnerships, which contain both individuals and companies as partners, are also ineligible. Not-for-profit organisations that don’t trade for profit fall outside the scope as well.
There’s one important rule for groups of companies. Associated companies, meaning companies under common control, must share a single £1 million AIA limit between them. Two sister companies cannot each claim £1 million separately. The same applies to companies that are part of a group structure, so if you’re running multiple entities, plan capital spend across the group rather than per company.
What assets qualify for AIA?
AIA covers most plant and machinery a business buys for its own use. Plant and machinery is a broad HMRC term that includes far more than industrial equipment.
Qualifying assets include:
- Machinery, tools, and manufacturing equipment
- Computers, laptops, tablets, and servers
- Office furniture including desks, chairs, and storage
- Vans, lorries, and most commercial vehicles
- Tractors and agricultural equipment
- Integral features of buildings such as electrical systems, heating, air conditioning, lifts, and water systems
- Solar panels and other renewable energy installations
- Fixed plant and fittings such as commercial kitchens or laboratory benches
- Demountable partitioning, alarm systems, and CCTV
The asset must be bought for use in the business, not for resale. It must also be used in the UK trade, and you must own it outright. Hire purchase agreements qualify, but pure operating leases do not because you don’t take ownership.
What does not qualify for AIA?
This is where most business owners trip up. Some assets that feel like obvious business purchases are specifically excluded from AIA.
The main exclusions are:
- Cars, including electric cars, which fall under a separate capital allowances regime based on CO2 emissions
- Land and buildings themselves, although integral features within a building do qualify
- Residential property, unless it forms part of a furnished holiday letting business
- Assets bought specifically to lease out to other businesses
- Assets received as gifts or transferred from personal use
- Items bought in the period the business permanently stops trading, with limited exceptions
Cars are the single biggest source of confusion. If your business buys a car, regardless of how it’s used, you cannot claim AIA on it. The vehicle goes into a separate capital allowances pool, and you claim writing down allowances instead. Vans, however, do qualify for AIA, which is why classification matters. HMRC treats a vehicle as a van if it’s primarily built to carry goods rather than passengers.
How much can you claim and what’s the limit?
The maximum AIA claim is £1 million per accounting period. Spend up to that figure on qualifying assets and you can deduct the full amount against your taxable profits.
The £1 million is pro-rated if your accounting period is shorter or longer than 12 months. A new company with a six-month first accounting period, for example, has an AIA limit of £500,000 for that period. The same applies if you extend an accounting period to 18 months, where the limit rises proportionally.
Accounting period length | AIA limit |
12 months | £1,000,000 |
9 months | £750,000 |
6 months | £500,000 |
18 months | £1,500,000 |
If your capital spend exceeds the £1 million limit in a single period, the excess doesn’t disappear. It goes into your capital allowances pool and qualifies for writing down allowances instead, at 18% per year for main pool assets and 6% per year for special rate pool items like integral features. The relief is still there, just spread over more years.
If you're approaching the £1 million limit and have major capital purchases planned, the timing of when you buy can shift relief between accounting periods. Bringing forward a purchase by a few weeks, or pushing it back, can be worth thousands in tax. Talk to your accountant before signing the order.
AIA in practice: a worked example
Let’s run the numbers on a realistic SME scenario.
A UK limited company, in its second year of trading, makes the following capital purchases during the accounting period:
Asset | Cost |
10 laptops for staff | £12,000 |
Office desks and chairs | £6,000 |
Commercial van for deliveries | £22,000 |
Total qualifying spend | £40,000 |
All three categories qualify for AIA. The company can claim the full £40,000 as an AIA deduction in the year of purchase.
Here’s how that flows through to the tax bill:
Calculation | Without AIA | With AIA |
Trading profit before capital allowances | £80,000 | £80,000 |
AIA deduction | £0 | (£40,000) |
Taxable profit | £80,000 | £40,000 |
Corporation tax at 25% | £20,000 | £10,000 |
Tax saved by claiming AIA | — | £10,000 |
At the 19% small profits rate, the same £40,000 deduction would save £7,600. Either way, the relief converts a capital purchase into an immediate, concrete reduction in tax owed.
The asset still has to be paid for, of course. AIA doesn’t make the equipment free. What it does is make sure the cost is deducted against profit in the year you actually spent the money, rather than spread thinly across a decade.
How to claim AIA on your tax return
Claiming AIA is part of your normal annual tax filing. There is no separate form or pre-approval process.
For limited companies, the steps are:
- Identify every qualifying asset bought in the accounting period
- Total the qualifying expenditure
- Enter the AIA claim in the capital allowances section of your CT600 corporation tax return
- Reduce your taxable profit by the AIA amount before calculating corporation tax due
- File the return with HMRC by the deadline
For sole traders and partnerships, AIA is claimed in the capital allowances section of your self assessment tax return, specifically the SA103 self-employment pages or SA800 partnership return.
You don’t submit invoices with the return, but you must keep them. HMRC can ask to see them during an enquiry, and you need:
- Purchase invoices showing date, supplier, and amount
- Evidence the asset is used for the business
- A capital allowances schedule or fixed asset register
- Proof of payment, particularly for items bought on hire purchase
Records must be kept for at least six years after the end of the accounting period for companies, and five years after the 31 January submission deadline for sole traders.
AIA and your accounting period
Timing matters with AIA. The claim must be made in the accounting period when the asset is first available for use in the business, not when you ordered it or when you paid the final installment.
For most outright purchases, the qualifying date is when the asset is delivered and ready to use. For hire purchase, you can claim AIA on the full cost when the asset is brought into use, even though you’re paying for it over time. For assets being built or constructed, the qualifying date is generally when the asset is finished and put into service.
If your business ceases trading, you can still claim AIA on qualifying assets bought during the final accounting period. The £1 million limit is pro-rated to the length of that period. However, the period of permanent cessation has restrictions on what counts as a qualifying purchase, so check with your accountant before making large capital purchases in your final year.
Newly incorporated businesses should also note that AIA is available from day one. There’s no minimum trading period before you can claim. If you register a UK limited company and buy equipment in your first month, the AIA applies to that first accounting period, pro-rated if shorter than 12 months.
What if your spend exceeds £1 million?
Capital spend above the AIA limit doesn’t lose all tax relief. It moves into the standard capital allowances regime and qualifies for writing down allowances.
The two main pools are:
- Main pool: most plant and machinery, written down at 18% per year on a reducing balance basis
- Special rate pool: integral features, long-life assets, and thermal insulation, written down at 6% per year
So if you spent £1.2 million on qualifying assets in one period, you’d claim £1 million as AIA and put the remaining £200,000 into the appropriate pool. You’d then get 18% (£36,000) of writing down allowance in that year for main pool items, with the balance carried forward to future years.
For most SMEs, the £1 million AIA limit comfortably covers annual capital spend. The pooling regime tends to matter mainly for asset-heavy businesses such as manufacturing, logistics, and hospitality.
Common AIA mistakes to avoid
A few errors come up repeatedly in HMRC enquiries:
- Claiming AIA on a car (cars never qualify, even electric ones)
- Claiming AIA on assets bought before the business started trading (pre-trading expenditure has its own rules)
- Forgetting to pro-rate the limit for short accounting periods
- Claiming AIA across associated companies without sharing the limit
- Missing the timing window by claiming in the wrong accounting period
- Including the VAT element when the business is VAT-registered (claim AIA on the net cost only; the VAT goes through your VAT return)
If you’re VAT-registered, your AIA claim should be on the cost excluding VAT. The VAT itself is reclaimed separately on your VAT registration for UK businesses returns. If you’re not VAT-registered, the full gross cost is the qualifying amount because you cannot reclaim the VAT.
AIA versus other capital reliefs
AIA isn’t the only capital allowance available, but for most SMEs, it’s the most generous and the simplest. Here’s how it compares at a high level:
Relief | Rate | Best for |
Annual Investment Allowance | 100% in year one | Most plant and machinery up to £1m |
Writing Down Allowance (main pool) | 18% per year | Spend above the AIA cap or assets that don’t qualify for AIA |
Writing Down Allowance (special rate) | 6% per year | Integral features, long-life assets |
Full Expensing | 100% in year one | Companies only, new plant and machinery, unlimited |
Full expensing was introduced in April 2023 and made permanent in 2024. For companies buying new, unused plant and machinery, full expensing offers a similar 100% first-year deduction but without the £1 million cap. Sole traders and partnerships can’t use full expensing, which is why AIA remains essential for unincorporated businesses.
For running a limited company, understanding which relief to apply first can affect your overall tax position, particularly if you’re buying second-hand assets that don’t qualify for full expensing.
How Sleek helps with capital allowances
Capital allowances are one of the easiest reliefs to under-claim because the rules sit across multiple sections of HMRC’s manuals and the asset classifications are not always obvious to non-accountants.
Sleek’s UK accounting team prepares your CT600 or self assessment return as part of a fixed-fee service, which includes reviewing your fixed asset register, identifying every qualifying purchase, and applying AIA, full expensing, and writing down allowances correctly. We also flag opportunities you may have missed in prior years, where amendments are still possible.
Disclaimer: The preceding information is not legal advice. This content is aimed to provide general guidance. For more formal or legal advice, contact Sleek directly.
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FAQs on annual investment allowance
Can I claim AIA on a second-hand asset?
Yes. AIA applies to both new and second-hand plant and machinery, provided the asset qualifies and is bought for use in your business. This is one of the key advantages of AIA over full expensing, which only covers new, unused assets. Buying a used commercial van, refurbished machinery, or pre-owned office equipment all qualify, as long as you own the asset outright.
What happens to AIA if I sell the asset later?
When you sell a qualifying asset you’ve claimed AIA on, the sale proceeds are treated as a balancing charge and added back to your taxable profits in the year of disposal. This effectively recovers some of the relief you claimed. The charge is capped at the original AIA amount, so you won’t pay tax on more than you saved. Keep accurate disposal records to calculate this correctly.
Can I claim AIA if I’m not yet making a profit?
Yes. AIA can create or increase a trading loss, which you can carry forward against future profits or, in some cases, carry back to earlier periods. Loss-making businesses still benefit from making the claim because the relief isn’t wasted, it’s banked. For companies, the loss can offset profits in the previous 12 months or be carried forward indefinitely against future trading profits.
Does AIA apply to assets bought on finance?
Yes, with one important condition. Hire purchase agreements qualify for AIA because you ultimately own the asset, and you can claim the full cost when the asset is brought into use, not when payments end. Pure leases and contract hire do not qualify because ownership never transfers. Check your finance agreement carefully, as the wording determines whether HMRC treats the arrangement as hire purchase or a lease.
Can I split AIA between different assets?
Yes. The £1 million limit is a total cap across all qualifying purchases in the accounting period, not a per-asset limit. You can spread your AIA claim across as many assets as you like, in any combination, up to the total. This flexibility means you should always claim AIA against your special rate pool items first, since those would otherwise only attract 6% writing down allowances rather than 18%.
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What records do I need to support an AIA claim?
You need purchase invoices showing the supplier, date, and amount, evidence the asset is used in the business, and a fixed asset register or capital allowances schedule listing each qualifying purchase. Companies must keep these records for at least six years after the end of the accounting period. Sole traders must keep them for at least five years after the 31 January self assessment deadline.
Can I amend a previous tax return to claim missed AIA?
Yes, within strict time limits. Companies can amend their CT600 within 12 months of the original filing deadline. Sole traders and partnerships have until 31 January, roughly 12 months after the original submission deadline, to amend a self assessment return. Beyond these windows, you can sometimes claim overpayment relief for up to four years, but the process is more complex and not all reliefs are recoverable.
