Understanding the Annual Investment Allowance for UK Businesses

The Annual Investment Allowance (AIA) is one of the most valuable capital allowances available to UK businesses. It allows you to deduct the full cost of qualifying plant and machinery from your profits in the year of purchase, rather than spreading the deduction over many years through Writing Down Allowances. For most small and medium businesses, it means capital expenditure provides an immediate and full tax reduction.

What Is the AIA Limit?

The AIA limit is currently £1,000,000 per year. This means that if you spend up to £1 million on qualifying plant and machinery in a tax year, you can deduct the entire cost from your taxable profits immediately. Any expenditure above £1 million falls into the Writing Down Allowance pools (18% or 6% per year).

What Qualifies for AIA?

Most plant and machinery used in your business qualifies, including computers and IT equipment, machinery and tools, office furniture, commercial vehicles (vans, lorries, trucks), and fixtures and fittings in business premises. Items specifically excluded from AIA include cars (though other allowances apply), items leased to others, items acquired on hire purchase where you do not own them, and gifts.

Cars

Cars do not qualify for AIA but do qualify for other allowances. New zero-emission cars qualify for a 100% First Year Allowance — you deduct the full cost in year one. Cars with CO2 emissions up to 50g/km (but not zero) go into the 18% main pool. Cars above 50g/km go into the 6% special rate pool.

How AIA Works

You claim AIA on your tax return (Self-Assessment for sole traders and partnerships, CT600 for limited companies). Enter the qualifying expenditure in the capital allowances section. The claim reduces your taxable profit by the full amount of the qualifying expenditure, up to the £1 million limit. If the deduction creates a loss, it can be carried back or forward according to the relevant loss relief rules.

Timing of Expenditure

The AIA is based on when you incur the expenditure, not when you pay. For cash purchases, these are the same. For credit purchases, it is the date of the invoice or delivery. For hire purchase, it is the date you take possession. Care is needed around the accounting period end — large purchases in the last week of an accounting period still qualify for that period's AIA.

Multiple Businesses

The AIA limit is shared between connected businesses (businesses under common control). If you have two sole trader businesses, they share one £1 million AIA. If you and your spouse each run separate businesses with no connection, each gets the full £1 million.

The Full Expensing Alternative

For limited companies (not sole traders or partnerships), 100% Full Expensing was made permanent in April 2023. This allows companies to deduct the full cost of qualifying new (not second-hand) plant and machinery in the year of purchase, with no upper limit. It works alongside AIA — for qualifying new assets, companies can use Full Expensing rather than AIA and can also claim 50% First Year Allowances on special rate assets.