A dental surgery refit feels like a single decision and arrives as a single invoice. For tax it is nothing of the sort. The same builder's figure has to be dissected into three quite different categories, and the way you draw the lines between them decides how quickly the cost turns into tax relief. Getting it right can pull years of relief forward; getting it wrong can leave a large slice of your spend crawling at 6% a year, or stranded with no plant relief at all.
This guide walks through how one fit-out invoice splits across the main-rate pool, the special-rate pool and the building structure, and then through the most valuable move in the whole exercise: pointing your Annual Investment Allowance at the slowest-relieving items first. We assume you already know what the AIA is; this page is about the anatomy of the spend it covers.
Why one fit-out invoice is really three tax categories
A surgery refit is never a single allowance. The expenditure splits three ways:
- Main-rate-pool plant and machinery. The general kit: dental chairs and delivery units, cabinetry, X-ray and imaging, autoclaves, compressors, suction, IT. This pool writes down fastest.
- Special-rate-pool integral features. Plant that has become part of the building: the electrical and lighting installation, water systems, heating, air conditioning and ventilation. This pool writes down slowest, at 6%.
- Non-qualifying building structure. Walls, floors, ceilings, doors and decoration. This gets no plant-and-machinery allowance at all, though it may instead reach the Structures and Buildings Allowance.
Getting this split right is what decides how fast relief comes. Two practices can spend an identical £150,000 and, depending only on how that figure is apportioned and where the AIA is pointed, end up with materially different tax positions in the early years. The mechanics here follow the standard capital-allowances framework for plant and machinery, and the worked numbers below are tagged to current 2026/27 rates.
The main-rate pool: 18% now, 14% from April 2026
General plant and machinery sits in the main-rate pool. In a dental fit-out that means the dental chairs and delivery units, surgery cabinetry and worktops, X-ray and imaging units, autoclaves, free-standing compressors and suction units, loupes and the IT estate. These attract the main-rate writing-down allowance on a reducing-balance basis.
The rate is changing, and you must date-tag it. The main-rate writing-down allowance is 18% for relief up to 31 March 2026 (corporation tax) or 5 April 2026 (income tax), and 14% for relief from 1 April 2026 (corporation tax) or 6 April 2026 (income tax), under Finance Act 2026 section 28. A chargeable or basis period that straddles the change date uses a hybrid rate, time-apportioned by days. This rate only bites on spend that sits above the AIA, because anything inside the £1m AIA is relieved in full immediately. The special rate, by contrast, was not changed and stays at 6%.
The special-rate pool: 6% integral features
The special-rate pool is the slow pool. It holds the integral features: the electrical and lighting installation, the cold and hot water systems, space and water heating, air conditioning and mechanical ventilation, and lifts. In a surgery refit these are not a footnote; they are a large slice of the spend. Compressed air and central suction need pipework and plant, local exhaust ventilation needs ducting and wiring, surgery-grade lighting is hard-wired into the lighting installation, and modern infection-control standards drive significant HVAC.
All of this attracts only 6% writing-down allowance on a reducing balance, a drag of roughly 38 years before most of the cost is relieved. That slow rate is precisely why the special-rate items are the ones you most want to cover with the AIA, as the next section explains.
What is not a capital allowance at all: the building structure
Some of the invoice is neither pool. The walls, floors, ceilings, doors, general decoration and the building shell are not plant and machinery. They get no plant-and-machinery allowance and no AIA. Instead they may qualify for the Structures and Buildings Allowance at 3% a year over 33 and a third years, which is a separate, much slower relief that companion guide covers in full.
Drawing this line wrong, by claiming AIA on building works, is the classic dental fit-out error. It inflates the year-one claim, and on enquiry HMRC will strip the structure out and leave you with an unexpected liability. The boundary between special-rate integral features (which do get relief, slowly) and building structure (which does not, except through SBA) is where most of the risk lives.
The reason the structure category is so easy to get wrong is that, to the eye, it looks like part of the same job. The plasterer, the electrician and the equipment installer are all on site in the same week, and the builder bills it as one project. But tax does not follow the project; it follows the asset. A new partition wall is structure even though it was built at the same time as the wiring that runs through it. A suspended ceiling is structure even though the ventilation ducting above it is an integral feature. The discipline is to ask of each item: is this the building, or is this apparatus the practice uses in the building? Walls, floors, ceilings and decoration are the building. Wiring, pipework, heating, cooling and the surgery kit are apparatus.
Where the structure does qualify for the Structures and Buildings Allowance, note two things. First, the SBA is a 3% straight-line relief over 33 and a third years, which is even slower than the special-rate pool, so it is no substitute for getting plant correctly into the pools. Second, the SBA has its own evidence requirement (an allowance statement) and excludes the land and any plant already pooled. Treat it as the residual home for genuine structure, not as a place to park spend you could not categorise.
The order that matters: direct AIA at the 6% items first
The AIA gives 100% relief on up to £1m of qualifying plant a year, and it can be allocated to either pool. This optionality is the heart of fit-out planning.
Because the special-rate pool writes down at only 6% a year, while the main pool writes down at 18% (14% from April 2026), the AIA is worth most when pointed at the 6% integral features first. Cover the slow-relieving special-rate spend with the AIA, take 100% of it this year, and leave the faster main-pool items to write down at the higher rate. Do it the other way round, putting the AIA on the fast main-pool items and leaving the integral features to crawl at 6%, and you have wasted the allowance on spend that would have relieved quickly anyway. This single allocation decision is the most valuable move in the article.
It helps to think about what the AIA is really buying you. The allowance does not change the total relief you will eventually get on a pooled asset; the pool relieves the full cost in the end whatever you do. What the AIA buys is speed: it converts a multi-year write-down into a single year-one deduction. Speed is worth far more on a slow pool than a fast one, because the slow pool is where the gap between immediate relief and natural write-down is widest. On the 6% pool, the difference between AIA and no AIA is the difference between all of the cost this year and almost four decades of crawling reductions. On the main pool, the difference is real but much smaller, because the asset relieves at a healthy clip anyway. Put bluntly, the AIA's value is concentrated in the slowest-relieving spend, and that is the integral features.
There is a second-order point that profitable practices should keep in mind. The value of any deduction depends on the rate of tax it saves. If you expect to be in a higher-rate or marginal band this year and a lower one next year, accelerating relief through the AIA also pulls it into the more valuable year. The allocation decision and the timing decision therefore interact, which is why a fit-out near year-end deserves a deliberate plan rather than a default.
A line-by-line dental fit-out, categorised
The table below walks a refit invoice item by item into its category. It is illustrative; the actual boundary on any given item depends on how it is installed and how it functions.
| Fit-out item | Category | Relief route |
|---|---|---|
| Dental chair and delivery unit | Main-rate pool | AIA or 18%/14% WDA |
| Surgery cabinetry and worktops | Main-rate pool | AIA or 18%/14% WDA |
| X-ray, OPG and imaging units | Main-rate pool | AIA or 18%/14% WDA |
| Free-standing compressor and suction | Main-rate pool | AIA or 18%/14% WDA |
| Electrical installation and rewire | Special-rate pool (integral feature) | AIA or 6% WDA |
| Surgery lighting installation | Special-rate pool (integral feature) | AIA or 6% WDA |
| Cold and hot water systems, waste plumbing | Special-rate pool (integral feature) | AIA or 6% WDA |
| Air conditioning, ventilation and air handling | Special-rate pool (integral feature) | AIA or 6% WDA |
| Partition walls and flooring | Building structure | SBA at 3% (no plant allowance) |
| General decoration and shell works | Building structure | SBA at 3% (no plant allowance) |
The borderline cases are where the value sits. A free-standing compressor is main-pool plant; the pipework distributing the compressed air around the surgery is closer to an integral feature. Surgery lighting panels are main-pool plant if they are free-standing fittings, but the hard-wired lighting installation they connect into is a special-rate integral feature. These judgments are exactly what a specialist apportionment exists to make.
It is worth dwelling on why these judgments matter so much in a dental setting specifically. A general office fit-out is mostly decoration, partitioning and a modest amount of wiring; the integral-feature slice is small. A dental surgery is the opposite. Infection control, compressed air, central suction, local exhaust ventilation, surgery-grade lighting and the cooling needed for imaging and decontamination rooms all drive a heavy services load. In a typical refit, the special-rate integral-feature slice can be a third or more of the qualifying spend, which is far higher than most owners expect. That is good news, because integral features do attract relief, but it makes the apportionment more valuable and the cost of getting it wrong higher. Understate the integral features and you lose relief; overstate them by sweeping in genuine structure and you expose the claim on enquiry.
One nuance to hold onto: an item's category is driven by what it is and how it functions, not by the heading on the builder's quote. A line called "electrical works" almost always belongs in the special-rate pool, but a line called "surgery equipment" might contain a mix of free-standing main-pool plant and plumbed-in fixtures. The apportionment has to look through the labels to the underlying assets.
The 40% first-year allowance and full expensing above the AIA
For spend that exceeds the £1m AIA, there are further reliefs, though they rarely bite for a single-site practice. A company can use full expensing (100% relief on new main-rate plant) and the 50% first-year allowance on new special-rate integral features, both uncapped but available only on new (not second-hand) assets. From 1 January 2026 a permanent 40% first-year allowance also applies to new main-rate plant for both companies and unincorporated businesses, excluding second-hand assets and cars (Finance Act 2026 section 29).
For most dental fit-outs these only matter above the £1m AIA ceiling, because below the cap the AIA gives 100% relief, which beats both 40% and 50%. The timing of the AIA is itself a planning lever, and a fit-out close to year-end raises exactly that question.
Why a specialist apportionment beats a builder's invoice
A builder bills "fit-out: £180,000" in one line. HMRC relief, though, depends on a just and reasonable apportionment of that figure across main pool, special rate and structure. A single-line invoice does not give you that, and it does not give you the costed schedule you need to defend the split on enquiry.
A specialist capital allowances apportionment routinely surfaces integral-feature and main-pool spend that a single-line invoice buries. We have seen a practice whose builder billed a £180,000 refit as a single line, where a specialist apportionment surfaced enough integral-feature spend to point the AIA at the 6% items first and pull years of relief forward that would otherwise have crawled. The exercise is not about inventing relief; it is about correctly identifying relief that is already in the spend and would otherwise be lost to a vague invoice.
The Capital Goods Scheme shadow on a big fit-out
If your practice is partly exempt, mixing exempt dental care with standard-rated cosmetic work, the same fit-out has a second tax life. Where the spend on land or buildings reaches £250,000 or more, it enters the VAT Capital Goods Scheme, which spreads and re-tests input-VAT recovery over 10 years as your taxable-use mix shifts. The capital-allowance pool split and the Capital Goods Scheme run on the same invoice but are different taxes. Keep them separate in your head, but make sure both are looked at on a large refit.
Disposal: balancing charges and balancing allowances
Allowances are not the end of the story. When a pooled asset is later sold or scrapped, its disposal value (capped at original cost) is deducted from the pool. If the pool turns negative, a balancing charge claws relief back as taxable income; if it is positive on cessation, a balancing allowance may be given. The point that catches people out: kit relieved in full by the AIA still carries a disposal value. Sell AIA-relieved equipment with the practice, or strip it out on a later refit, and a balancing charge can follow. These mechanics live in CAA 2001 sections 55 to 59, and the same disposal logic drives the value negotiation when you buy a practice with existing fixtures.
Records and the apportionment trail you must keep
The split is what HMRC tests on enquiry, so keep the evidence that supports it: the invoices, the specialist apportionment or surveyor's schedule, and the asset register showing how each item was categorised. A clean costed schedule that ties the builder's figure to the pools is the difference between a claim that holds and one that unravels. If you want to see the mechanics worked through end to end, the worked capital-allowances example walks a straight equipment claim through the numbers.
The standard of evidence HMRC looks for is not a single global figure but a methodology. A schedule that shows how the £180,000 was broken down, item by item, with a reasoned basis for each category and a value attached, is robust. A claim that simply asserts "£100,000 of plant" with nothing behind it is fragile, because there is no way to test whether the £100,000 was reasonable or whether building structure was swept in. The phrase that matters in the legislation and the case law is "just and reasonable", and the way you demonstrate that you were just and reasonable is the costed schedule. Keep it with the rest of the practice's permanent tax records, not just for the year of the claim, because the pool balances carry forward and the disposal calculations years later depend on knowing what went in and at what value.
A practical filing tip: tag the apportionment schedule to the specific accounting period in which the spend was incurred, and keep a note of which items took the AIA and which were left in the pool. When a later refit replaces some of those items, you will need to know their original category and cost to compute the disposal value correctly, and reconstructing that from memory five years on is exactly the kind of avoidable error that turns a routine refit into a balancing-charge surprise.
Worked examples
Example A: a £150,000 surgery fit-out split across the pools
A practice spends £150,000 (VAT-exclusive) refitting two surgeries in the 2026/27 period. A just-and-reasonable apportionment gives: main-rate plant (chairs, cabinetry, X-ray, compressor) £70,000; special-rate integral features (electrical, water, HVAC) £55,000; building structure (partitions, flooring, decoration) £25,000.
The £1m AIA comfortably covers all £125,000 of qualifying plant. The order is what matters: direct the AIA at the £55,000 special-rate items first, because they would otherwise crawl at 6%, then the remaining £70,000 at the main-rate plant. All £125,000 of qualifying plant is relieved in full this year. The £25,000 of structure gets no plant allowance, but may reach the Structures and Buildings Allowance at 3%. (Tagged 2026/27, house position §7.)
Example B: why the AIA direction matters when spend exceeds the cap
Now imagine a group fit-out of £1.2m forces some spend out of the AIA. Putting the main-pool items outside the AIA loses far less than leaving the special-rate items outside it. Take the £55,000 of integral features: relieved at 6%, year-one relief is just £3,300, and it takes roughly 38 years to write down. The same £55,000 inside the AIA is relieved in full immediately. That gap, £3,300 in year one versus £55,000, is the whole case for pointing the AIA at the 6% pool first. (Tagged 2026/27, house position §7.)
Example C: the 14% rate change on the residual main pool
A company with a 31 March year-end has £40,000 of main-pool spend that did not fit inside the AIA, in an accounting period straddling 1 April 2026. The writing-down allowance on that pool is a hybrid of 18% (for the part of the period before 1 April) and 14% (for the part after), apportioned by days. A period split evenly across the date gives a blended rate of about 16% for that year, against a flat 14% for a wholly post-April year. The practical lesson: above-AIA main-pool spend relieves more slowly from April 2026 onward, which sharpens the case for using the AIA fully rather than letting spend fall into the pool. (Tagged companies 1 April 2026 / income tax 6 April 2026, house position §7.)
Common errors
- Claiming AIA on building structure, when the structure gets no plant allowance (only possibly SBA at 3%).
- Dumping the whole fit-out into the main pool and missing the 6% integral features (or vice versa).
- Pointing the AIA at fast 18%/14% main-pool items and leaving the slow 6% integral features to crawl.
- Ignoring the post-April-2026 14% main rate when modelling spend above the AIA, and quoting a flat 18%.
- Forgetting that AIA-relieved kit still carries a disposal value, and being surprised by a balancing charge on a later sale or refit.
The fit-out is one of the few moments in a practice's life where a single decision, the pool split and where the AIA is pointed, moves real money. It rewards getting the categories right and the order right, and it punishes a vague single-line invoice. Treat the split as a tax exercise in its own right, not a footnote to the builder's quote.