Capital allowances are the government’s way of acknowledging that buying business assets costs money — and that the tax system should reflect that. Rather than deducting the full cost of a piece of equipment as an expense (which most day-to-day costs allow), capital allowances give businesses a structured way to deduct the cost of longer-lasting assets from their taxable profits.

In our experience, this is an area where owner-managed businesses consistently leave money on the table. Not through any fault of their own — the rules are genuinely complex, and the landscape has shifted considerably over the last few years, particularly with the end of the super-deduction and the introduction of full expensing. Getting it right can make a meaningful difference to your corporation tax or income tax bill.

This post sets out how the main allowances work, who can claim what, and where we tend to see the most common mistakes.

Capital allowances apply primarily to plant and machinery — a broad category that covers far more than it sounds. Computers, vans, specialist equipment, tools, and certain fixtures within commercial premises can all qualify. For trades and construction businesses, that list extends to scaffolding, plant hire equipment, and site machinery.

What doesn’t qualify is worth noting too. Stock — things you buy to sell on — is not covered. Furniture or fittings inside a residential let property fall outside the rules (though furnished holiday lets and commercial property fixtures are a different matter). Land doesn’t qualify, and neither do most standard buildings, though there are separate allowances for structures and buildings that we’ll come to.

One rule that catches people out: if you use the cash basis for accounting — which many sole traders do — you generally cannot claim capital allowances, except on cars. The cash basis treats most asset purchases as ordinary expenses instead. It is worth reviewing whether cash basis is actually working in your favour before assuming it is the simpler option.

The key categories of allowances are the Annual Investment Allowance (AIA), full expensing (for companies), writing down allowances, and the structures and buildings allowance. Each has its own rules, rates, and eligibility criteria.

For most small and medium-sized businesses, the Annual Investment Allowance (AIA) is the workhorse relief. It currently allows businesses to deduct up to £1 million of qualifying plant and machinery expenditure in full in the year of purchase. For the vast majority of owner-managed businesses, this limit is more than sufficient — they will never spend £1 million on qualifying assets in a single year.

The AIA is available to sole traders, partnerships, and limited companies alike, which makes it the most broadly useful allowance on the list.

For limited companies, there is an additional route introduced from 1 April 2023: full expensing. This allows a company to deduct 100% of the cost of new and unused qualifying plant and machinery from profits before tax in the year of purchase — with no annual cap. A 50% first-year allowance applies to certain assets that fall into the ‘special rate pool’ (such as long-life assets and integral features), though you cannot claim both full expensing and the 50% allowance against the same item of expenditure.

It is worth noting that full expensing applies only to companies, only to new assets (not second-hand), and does not cover cars. If your business is still operating as a sole trader or partnership, you are relying on the AIA — which is still generous, but the distinction matters for planning purposes.

When expenditure exceeds the AIA limit, or for assets that don’t qualify for the AIA, writing down allowances (WDAs) come into play. These spread the tax relief over multiple years rather than giving it all upfront.

The main rate pool allows a deduction of 18% per year on a reducing balance basis. The special rate pool — which covers integral features of buildings (electrical systems, heating, air conditioning), long-life assets, and thermal insulation — uses a lower rate of 6% per year.

In practice, for most small businesses spending within the AIA limit, WDAs are a fallback rather than a primary planning tool. But for larger capital-intensive businesses — contractors with heavy plant, construction firms, or manufacturers — understanding the pools matters for forecasting the timing of tax relief accurately.

One thing worth flagging: when you sell or dispose of an asset, you may trigger a balancing charge, which effectively claws back some of the allowances you’ve already claimed if the sale proceeds exceed the remaining pool value. This is why asset disposals need to be reviewed carefully, not just acquisitions.

Since October 2018, businesses that incur costs constructing, converting, or renovating non-residential commercial structures have been able to claim the structures and buildings allowance (SBA). It provides relief at 3% per year on a straight-line basis — meaning it takes around 33 years to claim full relief, which is far less generous than plant and machinery allowances.

For property investors and businesses that own their commercial premises, the SBA is worth understanding even if it sounds modest. The cumulative effect over time is real, and it is an allowance that gets missed when property costs are lumped together without proper analysis of what qualifies.

Enhanced rates are also available in Freeport and Investment Zone special tax sites, which may be relevant to businesses operating in those designated areas — though those specific provisions are fairly niche and come with their own conditions and time limits.

Where this gets genuinely complicated — and where we see the most confusion — is with mixed-use properties and embedded fixtures. A commercial building purchase often contains items that qualify as plant and machinery (lighting, heating systems, specialist fit-out) alongside the structure itself. Separating these correctly can significantly increase the allowances available. This is an area where professional analysis tends to pay for itself.

Capital allowances mistakes tend to fall into a few recurring patterns. The most common is simply not claiming — either because the business owner assumes their accountant has handled it, or because they weren’t aware an asset qualified. Both are more common than you’d expect.

A second issue is timing. Capital allowances are given for the accounting period in which the expenditure occurs — for companies, that is their accounting period, which cannot exceed 12 months. Buying a significant piece of equipment just after your year-end rather than just before it can push the relief back by 12 months. For businesses with strong profits in a particular year, that timing decision has a real cash-flow implication.

Third, and something we feel strongly about flagging: there is a market of firms that contact business owners — particularly property owners — with high-pressure pitches around capital allowance surveys and retrospective claims. Some of these are legitimate; others are aggressive or poorly structured. If someone contacts you unsolicited about a large capital allowances claim, treat it with real caution. Any meaningful claim should be reviewed carefully, and transactions involving capital allowances should be assessed within a reasonable timeframe to ensure proper compliance.

Finally, sole traders using the cash basis should revisit that choice periodically. The simplicity benefit has to be weighed against what it costs in allowances forgone — particularly if asset purchases are a meaningful part of annual spending.