What Is AIA in Tax? A Guide for UK Landlords and Property Investors

AIA stands for Annual Investment Allowance. It is a capital allowance that lets a business write off the full cost of qualifying plant and machinery against its taxable profits in the year the money is spent, instead of spreading the relief across many years. The annual cap is £1 million, and that figure is permanent.

For property investors, AIA sounds like one of the most generous reliefs available. The catch is that most ordinary buy-to-let landlords cannot use it on the things they assume they can, because a long-standing rule blocks capital allowances for plant inside a let home. Understanding that single rule is the difference between a correct claim and an HMRC enquiry.

This guide explains what AIA is, how it works, the £1 million permanent cap, and the dwelling-house restriction that decides whether AIA applies to your property at all. It also covers commercial and mixed-use property, furnished holiday lets after abolition, property companies, the 2026 capital allowance changes, and how AIA sits alongside Making Tax Digital.

What Is AIA in Tax? A Plain Definition

The Annual Investment Allowance is set out in the Capital Allowances Act 2001 (CAA 2001), sections 51A to 51N. It gives 100% relief on qualifying capital expenditure on plant and machinery, up to a fixed annual limit, in the chargeable period in which the spend is incurred.

An ordinary capital cost would normally be relieved slowly through writing-down allowances, a percentage of the remaining value each year. AIA short-circuits that. If you spend £40,000 on qualifying plant and machinery and the spend is within your AIA cap, you deduct the whole £40,000 from your taxable profit that year.

The cap is £1 million per 12-month chargeable period. Per CAA 2001 section 51A(5), the maximum allowance is £1,000,000, and that figure was made permanent by Finance (No. 2) Act 2023 section 8 with effect from 1 April 2023. There is no longer a temporary cap and no scheduled fall back to £200,000. You should treat the £1 million figure as the settled, ongoing limit.

Does AIA Apply to My Buy-to-Let? The Dwelling-House Rule

This is the rule that catches most landlords out, so it comes first. CAA 2001 section 35 bars plant and machinery allowances, and therefore AIA, for expenditure on plant or machinery for use in a dwelling-house within an ordinary property business. The operative wording in section 35(2) is that the expenditure "is not qualifying expenditure if it is incurred in providing plant or machinery for use in a dwelling-house."

In plain terms, if you buy a boiler, a fitted kitchen appliance, a radiator, carpets or furniture for use inside a let house or flat, you cannot claim AIA or any other plant and machinery allowance on it. The asset is otherwise perfectly good plant and machinery, but the location, inside a dwelling let as residential accommodation, removes it from the allowance entirely.

There are narrow but genuine exceptions, and these are where property capital allowances claims still live:

• Common parts of a multi-let building. Plant serving the shared areas of a block of flats or an HMO, such as a communal boiler, a lift, communal lighting or a shared ventilation system, is not inside any individual dwelling, so it can qualify.
• Genuinely commercial or mixed-use space. Plant in offices, shops, commercial units or the non-dwelling parts of a mixed-use building is not caught by section 35. Integral features in those areas (electrical systems, cold water systems, heating, lifts, external solar shading under CAA 2001 section 33A) are special-rate plant and can qualify.
• Equipment used to run the business. Office equipment, computers and management software used to run your property portfolio, and not located in a let dwelling, are not inside a dwelling-house and can qualify.

So the dwelling-house rule does not mean a landlord never claims capital allowances. It means the claim sits in the common parts, in commercial and mixed-use space, and in the running of the business, not in the let homes themselves.

If Not AIA, How Do I Relieve Furniture and Appliances?

Because section 35 blocks AIA on items inside a let dwelling, the cost of furnishing and equipping a residential let is relieved a different way. For replacing worn-out domestic items, the route is replacement of domestic items relief under ITTOIA 2005 section 311A (with an equivalent in the Corporation Tax Act 2009 for companies).

This relief is a revenue deduction, not a capital allowance. It gives a deduction for the cost of replacing domestic items provided for use in a let dwelling, such as beds, sofas, carpets, curtains, fridges, freezers, washing machines and crockery. Three points matter:

• It applies to replacement of an item, not the first time you provide it. The old item must no longer be available for use in the property.
• It does not extend to fixtures (things that become part of the building, such as a fitted kitchen or a boiler), which follow the repairs-versus-capital rules instead.
• You cannot claim both this relief and a capital allowance on the same spend, so the routes do not overlap.

For repairs to the property itself, the cost is usually a revenue expense deductible in full. The line between a repair (revenue) and an improvement (capital) is one of the most common areas of error. Our complete list of landlord tax deductions explains the repairs-versus-capital distinction and replacement of domestic items relief in detail.

What Actually Qualifies for AIA on Property?

Pulling the rules together, here is what a property investor can and cannot claim AIA on. The table is a starting point, not a substitute for advice on your own facts.

Item and location	AIA available?	Why / what applies instead
Boiler, radiators, carpets, white goods inside a let house or flat	No	Section 35 dwelling-house bar. Use replacement of domestic items relief or revenue repairs.
Furniture and furnishings in a residential let	No	Section 35 bar. Replacement of domestic items relief (ITTOIA 2005 s.311A).
Communal boiler, lift or lighting in a block of flats or HMO common parts	Yes	Not inside an individual dwelling, so section 35 does not bite.
Plant and integral features in a commercial unit, office or shop	Yes	Not a dwelling. Integral features are special-rate plant (s.33A).
Fit-out plant in the commercial parts of a mixed-use building	Yes (commercial part)	Apportion between dwelling and non-dwelling parts.
Office equipment and computers used to run the portfolio	Yes	Not located inside a let dwelling.
Cars	No	Cars are excluded from AIA (CAA 2001 s.38B, General Exclusion 2). Separate rules apply.
The building structure itself	No	Buildings are excluded from plant and machinery (s.21). Structures and buildings allowance may apply to commercial buildings.

Two further exclusions are worth flagging. Cars never qualify for AIA. The building shell and its general fabric (walls, floors, ceilings, doors, windows, mains services) are treated as building, not plant, under CAA 2001 section 21, and so fall outside AIA. For commercial buildings, the structure may instead attract the structures and buildings allowance at 3% straight-line, which is a separate relief from AIA.

AIA on Commercial and Mixed-Use Property

Where the dwelling-house rule does not apply, AIA becomes genuinely valuable. Investors holding shops, offices, warehouses, surgeries or other commercial property can claim AIA on qualifying plant and machinery and integral features, and on fit-out costs when refurbishing a commercial unit.

Mixed-use buildings, for example a shop with a flat above, need apportionment. The plant serving the commercial part can qualify; the plant inside the residential dwelling is barred by section 35. A reasonable apportionment is required where an item serves both.

When you buy a commercial property that already contains fixtures (air conditioning, electrical systems, lifts), claiming allowances on those fixtures depends on the fixtures rules, including the section 198 election between buyer and seller and the pooling and fixed-value requirements that apply to post-April-2014 transactions. These rules are detailed and time-limited, so a fixtures claim on a commercial purchase is an area where specialist input pays off. For the full decision framework on commercial and residential capital allowances, see our capital allowances for property investors pillar guide.

AIA After the Furnished Holiday Lettings Abolition

Before April 2025, a qualifying furnished holiday let (FHL) was treated as a trade, which meant plant and machinery in the property, including furniture and appliances, qualified for capital allowances and AIA. The dwelling-house bar did not bite on an FHL in the same way.

That changed when the FHL regime was abolished by Finance Act 2025 Schedule 5, with effect from 6 April 2025 for income tax and 1 April 2025 for corporation tax. Properties that were FHLs are now taxed as part of an ordinary property business, which means the section 35 dwelling-house bar applies to them going forward.

The transitional position is important. Capital allowance pools built up on a former FHL before abolition are not lost. They carry forward into the ordinary property business pool and continue to be written down. What you cannot do is claim new AIA on plant and machinery inside those properties after the abolition date, because they are now ordinary residential lets caught by section 35. Genuinely serviced accommodation that amounts to a trade is a separate question, and you should take advice on the correct treatment.

AIA for Property Companies

If you hold property through a limited company, the rules work the same way on the dwelling-house point. Plant inside the company's let dwellings is barred by section 35; plant in commercial property and in common parts can qualify. Companies claim capital allowances, including AIA, through the corporation tax return.

A company has a single £1 million AIA across all its qualifying activities (section 51B). Where companies are under common control and related to one another, they share one £1 million allowance between them (sections 51E to 51G), so a group cannot multiply the allowance by setting up more companies. The detail of allocating the cap across a group is set out in our AIA £1 million cap allocation and association rules guide.

A company investing in new and unused main-rate plant for genuinely commercial property will often use full expensing rather than AIA, because full expensing gives 100% relief with no annual cap. The next section explains how AIA, full expensing and the new 40% allowance fit together. If you are weighing up incorporation, our complete guide to buy-to-let limited companies covers the wider tax picture.

AIA, Full Expensing and the New 40% First-Year Allowance

AIA is one of several capital allowances. For property investors, three matter most alongside it.

• Full expensing under CAA 2001 section 45S gives companies a 100% first-year allowance on new and unused main-rate plant and machinery, with no annual cap. It is company-only and is not available to individual landlords or partnerships.
• The 40% first-year allowance introduced by Finance Act 2026 section 29 gives a 40% first-year allowance on new and unused main-rate plant and machinery for spend incurred on or after 1 January 2026. It excludes cars, second-hand assets and assets for overseas leasing. It is the practical route for those who cannot use company-only full expensing, such as unincorporated landlords and leasing businesses. Unlike the first-year allowances, AIA itself can cover second-hand qualifying plant, as our guide on claiming AIA on second-hand assets explains.
• Writing-down allowances apply to spend above the AIA cap, or to assets that do not qualify for a first-year allowance. The main pool rate is 14% from April 2026, cut from 18% by Finance Act 2026 section 28, and the special rate pool (integral features) stays at 6%. Periods straddling the start date use a time-apportioned hybrid rate. See our guide to writing-down allowance rates for the detail.

The key point for a property investor is that all of these reliefs are still gated by section 35. None of them lets you claim against plant inside a let dwelling. They become relevant only on the commercial, common-parts and business-equipment spend that section 35 does not block. For an investor-focused comparison of AIA against full expensing, see our AIA for UK property investors guide.

How AIA Interacts With Section 24

Section 24 restricts finance-cost relief for individual landlords to a basic-rate (20%) tax reducer, rather than a full deduction. It is fully in force. AIA is a different mechanism: it is a deduction from rental profit, not a finance cost, so it is not restricted by Section 24.

Where a landlord does have a valid capital allowances claim (for example on common parts or commercial space), that claim reduces rental profit in the normal way before the Section 24 calculation runs. For a higher-rate taxpayer, reducing taxable rental profit is valuable because it lowers income that would otherwise be taxed at 40% or 45%. Our complete guide to Section 24 sets out how the finance-cost restriction works in full.

How the £1 Million AIA Cap Works in Practice

The £1 million cap is a permanent annual limit, applied per chargeable period of 12 months. If your accounting period is shorter or longer than 12 months, the cap is scaled in proportion. A six-month period, for instance, has a £500,000 cap.

Spend up to the cap gets 100% relief in the year. Spend above the cap is not lost; it rolls into the relevant capital allowances pool and is written down at the pool rate (14% main pool, 6% special rate) in later years. For investors planning a large refurbishment of commercial space, the timing of qualifying spend across chargeable periods can change how quickly the relief lands. The cap-allocation and group-sharing mechanics are covered in depth in our guide to the Annual Investment Allowance and the £1 million cap.

How to Claim AIA

You claim AIA through your tax return. Individual landlords use the capital allowances boxes on the Self Assessment property pages (SA105). Companies claim through the corporation tax return (CT600) and the supporting computations.

For each chargeable period you identify the qualifying spend, claim AIA up to the cap, and carry any excess into the pool for writing-down allowances. Good records are essential. Keep invoices, the date each asset was bought, and evidence of when it was first brought into use, because HMRC can ask for this if it reviews your return. For fixtures bought as part of a commercial property, you may need a capital allowances valuation and a section 198 election with the seller, which is a specialist exercise.

Non-Resident Landlords and AIA

Non-resident landlords are within the charge to UK tax on their UK property income and are subject to the same capital allowances rules, including the section 35 dwelling-house bar. A non-resident with UK residential lets faces the same restriction as a UK-resident landlord; allowances are available on common parts and commercial space, not on plant inside the let homes.

Non-resident landlords in the Non-Resident Landlord Scheme can apply (using form NRL1) to receive rent without tax deducted at source and account for their income, including any capital allowances, through Self Assessment. Non-resident companies holding UK property claim through the corporation tax return, with the same £1 million AIA cap.

AIA and Making Tax Digital for Landlords

Making Tax Digital (MTD) for Income Tax is live and being phased in by income level. It applies from 6 April 2026 to landlords and sole traders with qualifying income over £50,000, from 6 April 2027 to those over £30,000, and from 6 April 2028 to those over £20,000.

Within MTD you keep digital records and send quarterly updates to HMRC using compatible software, then finalise the year with a final declaration. Capital allowances, including any AIA claim, are dealt with at the final declaration rather than within the quarterly updates, so your record-keeping needs to capture qualifying spend through the year ready for the year-end adjustment. Our guide to MTD for landlords sets out the thresholds and what you need to do to be ready.

Common Mistakes Landlords Make With AIA

The errors below are the ones we see most often, and several can trigger an HMRC enquiry.

• Claiming AIA on plant inside a let dwelling. This is the biggest and most expensive mistake. Boilers, kitchens, carpets and furniture in residential lets are barred by section 35. Claiming AIA on them is wrong and will be challenged.
• Believing the cap is temporary or about to fall to £200,000. The £1 million cap is permanent. Old guidance that says otherwise is out of date.
• Treating the main pool writing-down rate as 18%. It is 14% from April 2026.
• Confusing repairs with capital spend. Repairs are usually a revenue deduction in full; capital spend follows the allowances rules. Getting this line wrong distorts the return.
• Missing the section 198 election deadline on a commercial purchase. Without it, a buyer can lose the right to claim on fixtures already pooled by the seller.
• Assuming individuals can use full expensing. Full expensing is company-only. Unincorporated landlords use AIA or the 40% first-year allowance instead.

Getting Professional Advice

AIA can deliver real relief on commercial and mixed-use property and on the common parts of blocks and HMOs, but the dwelling-house rule, the repairs-versus-capital line and the fixtures rules make it one of the easier areas to get wrong. A mistaken claim is not just denied; it can open an enquiry into the whole return.

A specialist property accountant can review your expenditure, separate what genuinely qualifies for AIA from what should go through replacement of domestic items relief or revenue repairs, handle fixtures elections on commercial purchases, and keep your claims correct as the 2026 rate changes bed in. To understand what that involves, see what a property accountant does.

You can also cross-check the headline rules at the official source: GOV.UK publishes a consumer-level overview of the Annual Investment Allowance. For your own portfolio, the right next step is a conversation about what actually qualifies before you spend.