Annual Investment Allowance (AIA) and Full Expensing: A Business Tax Guide

Capital allowances are the mechanism by which businesses obtain tax relief on spending on plant and machinery — the UK does not permit a simple deduction of capital expenditure against profits in the year it is incurred. Instead, capital allowances determine the rate and timing of tax relief. The Annual Investment Allowance (AIA) and, since April 2023, full expensing, provide accelerated 100% first-year relief on qualifying expenditure, making them the most valuable tax tools for businesses investing in equipment, machinery, and fixtures.

What Is the Annual Investment Allowance?

The AIA provides a 100% deduction in the year of expenditure for qualifying plant and machinery. It does not require the business to write down the asset over its useful life — the full cost is deducted immediately, reducing taxable profits in the year of purchase.

The AIA limit is £1,000,000 per annum. Having previously been set at temporary higher levels on a time-limited basis, the £1m limit was made permanent, so no reversion to a lower figure is scheduled. Any expenditure on qualifying assets above the £1m limit falls into the standard capital allowance pools (main pool or special rate pool) and attracts the normal writing-down allowances.

The AIA is available to:

• Sole traders and partnerships
• Limited companies (including close companies)
• Individuals carrying on a property business that includes commercial property (for fixtures)

The AIA is not available to individuals or trusts for non-business use assets, or to investment companies whose activities are limited to holding shares.

What Qualifies for AIA?

Qualifying plant and machinery includes most tangible assets used in a business, such as:

• Manufacturing and processing equipment: machinery, tools, computer hardware.
• Vehicles: commercial vehicles used for business (but see the exclusion for cars below).
• Fixtures: plant and machinery that is permanently attached to a building — boilers, air conditioning, electrical systems installed as part of a building project, fire alarm systems, plumbing.
• Integral features of a building (see Special Rate Pool section below): these qualify for AIA even though they would otherwise attract the slower 6% writing-down rate.
• Office furniture, shelving, display units, and similar operational assets.

What Does NOT Qualify for AIA?

Cars are specifically excluded from the AIA and from full expensing. Cars (defined by HMRC as vehicles primarily suited for personal use, not modified commercial vehicles) must be allocated to the main or special rate pool and written down at the main-pool or special-rate-pool rate per annum respectively, depending on their CO2 emissions, unless they are 100% electric (which qualify for 100% first-year allowances under separate provisions).

Buildings and structures: the cost of constructing or purchasing a building does not qualify for AIA. A separate Structures and Buildings Allowance (SBA) provides 3% straight-line relief on qualifying construction costs, but this is much slower than AIA.

Land: no capital allowances are available on land.

Assets held for leasing may qualify for AIA but with restrictions; specific leasing provisions in the Capital Allowances Act 2001 should be reviewed.

The Special Rate Pool and Integral Features

Certain assets must be allocated to the special rate pool rather than the main pool. The special rate pool attracts writing-down allowances at only 6% per annum (reducing balance method). Assets allocated to the special rate pool include:

• Integral features of a building: electrical systems (including lighting), cold water systems, space or water heating systems, powered systems of ventilation, lifts and escalators, and external solar shading.
• Long-life assets: assets with an expected useful life of 25 years or more (e.g., some industrial machinery, offshore platforms).
• Thermal insulation added to existing buildings.

Critically, integral features qualify for the AIA. A business can therefore claim 100% relief in year one on integral features by using AIA against them, rather than falling into the 6% pool. This is a significant planning opportunity for businesses undertaking building fit-outs or refurbishments.

The priority order for claiming AIA matters: it is generally more tax-efficient to use the AIA against special rate pool assets (which would otherwise attract only 6% relief) rather than main pool assets (which attract the lower main-pool writing-down rate — 14% from April 2026, reduced from 18%). The remaining AIA capacity can then be applied to main pool assets.

Full Expensing: From April 2023

Full expensing was introduced from 1 April 2023 for companies only (not sole traders or partnerships). It provides:

• 100% first-year allowance on expenditure on main pool assets (replacing the standard main-pool writing-down rate of 14% from April 2026).
• 50% first-year allowance on expenditure on special rate pool assets (the balance entering the pool at 6%).

Full expensing is available on an unlimited basis — unlike the AIA, it has no annual cap. This makes it particularly valuable for large companies making capital expenditures in excess of £1m in a year.

AIA vs Full Expensing: Which to Use?

For companies spending more than £1m on qualifying assets:

• Full expensing (100% for main pool, 50% for special rate) applies to all expenditure within its scope.
• AIA provides 100% on special rate assets — making it more valuable than the 50% first-year allowance under full expensing for those assets.

The optimal approach is:

1. Use AIA against special rate pool assets first (achieving 100% relief vs the 50% that full expensing would deliver).
2. Use AIA against remaining main pool assets up to the £1m limit.
3. Apply full expensing (100%) to main pool assets beyond the AIA limit.
4. Apply full expensing (50%) to special rate assets beyond the AIA limit.

For companies spending below £1m, AIA alone is generally sufficient and simpler to administer.

Important: full expensing is a company relief only and requires the asset to be new (unused). Second-hand assets do not qualify for full expensing (though they do qualify for AIA, provided they are first brought into use by the business).

Straddling Accounting Periods

Where a business has a 12-month accounting period that straddles the date of an AIA limit change, the available AIA is calculated by reference to the proportionate limit for each part of the period. For example, if the limit changes on 1 April and the accounting period runs from 1 January to 31 December, the maximum AIA is:

• 3/12 × (old limit) + 9/12 × (new limit)

Additionally, expenditure incurred in the straddling period is subject to a cap equal to the relevant proportion of the limit for each part of the period. This is often a source of error in practice and should be calculated carefully with the company's accountants.

Group Companies and the Shared AIA Limit

Where two or more companies are under common control and form a group, the £1m AIA limit is shared between all companies in the group — they do not each get a separate £1m allowance. The group may allocate the AIA between companies as they choose, but the combined claim cannot exceed £1m.

Common control is broadly defined: companies under common control includes any relationship where one person controls multiple companies, or where multiple persons together control companies within the same group. This can catch family-owned groups and associated company structures that may not appear to be formally connected.

The group company restriction means that investment planning within groups must be coordinated across all entities to ensure the AIA is used efficiently.

Interaction with the Super-Deduction (Now Repealed)

The 130% super-deduction was available from 1 April 2021 to 31 March 2023. It has been repealed and replaced by full expensing. Assets that attracted the super-deduction and were subsequently disposed of may give rise to a balancing charge at the higher rate; this is a transitional issue relevant for assets purchased in 2021–2023.

Disposal and Balancing Charges

When an asset on which AIA has been claimed is sold, the proceeds are added back to the relevant pool. Where proceeds exceed the pool balance, a balancing charge arises — additional taxable profits equal to the excess. This ensures that the tax relief ultimately equals the net cost of the asset (cost minus proceeds).

Where full expensing has been claimed (for companies), the disposal treatment is modified: the proceeds from disposal of a fully expensed asset are subject to a balancing charge at the applicable rate. Businesses should model disposal proceeds when budgeting for asset replacement.

Compliance Caveat

Capital allowances legislation is detailed and subject to change. The full expensing regime is stated to be permanent (from April 2023 onwards) but parliamentary confirmation should be monitored. AIA limits, first-year allowance rates, and the eligible asset categories are all subject to change in Finance Acts. The specific inclusion of an asset as "plant and machinery" rather than a building or structure is often a matter of fact and degree, and HMRC may challenge categorisations on enquiry. Property-related capital allowances are particularly complex, especially where a business is buying a property with existing fixtures — a s.198 election agreed between buyer and seller is required to establish the value attributed to fixtures in the purchase price. Professional tax advice is recommended for significant capital expenditure programmes. This guide reflects the law as at June 2026.

How Global Investments Can Help

Global Investments advises business-owning clients on the tax efficiency of their capital expenditure programmes, including how to maximise AIA and full expensing claims, how to structure group capital investment across multiple entities, and how capital allowances interact with broader tax planning. For property investors, we also advise on capital allowances on commercial property acquisitions and fit-outs. Contact us to discuss your capital expenditure plans.