Use this free Writing Down Allowance Calculator UK to estimate main pool WDA, special rate pool WDA, hybrid rates, closing tax written down value and year-by-year capital allowance relief for plant and machinery.
Writing Down Allowance is the annual UK capital allowance that reduces a tax pool balance over time.
Writing Down Allowance, usually shortened to WDA, is one type of UK capital allowance. It lets a business deduct a percentage of the remaining tax value of certain assets from taxable profits each year. In simple terms, if your business has plant and machinery that has not already been fully relieved through the Annual Investment Allowance, full expensing, a first-year allowance or another upfront relief, the unrelieved amount normally sits in a tax pool and is written down gradually.
This is different from accounting depreciation. Depreciation appears in your accounts and follows your chosen accounting policy, such as straight-line depreciation over five years or reducing balance depreciation at 25%. Writing Down Allowance is a tax calculation. It follows HMRC rules, uses statutory rates, and affects the tax computation rather than the profit and loss account directly. At year end, many businesses add back accounting depreciation and then claim capital allowances instead.
For 2026, the most important WDA rates are the 14% main pool rate and the 6% special rate pool rate. The main pool usually covers general plant and machinery, equipment and some low-emission cars. The special rate pool covers integral features, long-life assets, solar panels, thermal insulation added to buildings and cars over the relevant emissions threshold. This Writing Down Allowance Calculator UK helps you model both pools and see how relief spreads over future years.
Enter your opening pool balance, additions, disposals, period length and tax rate to generate a year-by-year WDA schedule.
Use this tab for main pool plant and machinery after AIA or other first-year relief has been applied. The default main pool WDA rate is 14% for periods beginning after the 2026 change date.
Use this tab for integral features, long-life assets, solar panels, thermal insulation added to buildings and cars that belong in the special rate pool.
Use this tab when your accounting period spans the April 2026 main rate change. The calculator blends 18% and 14% based on days before and after the change date.
Year 1 uses the blended rate. Later years use 14% main pool WDA in this projection.
Use the custom tab for planning scenarios, single asset pools, internal forecasts, or checking how different rates change the timing of relief.
The calculation is simple, but the order of additions, disposals and allowances matters.
Start with the opening tax written down value of the pool. Add any qualifying expenditure that has not already been fully relieved. Deduct disposal proceeds for assets sold or scrapped, usually capped at the original cost of the asset. The remaining figure is the base on which the WDA percentage is applied. The allowance reduces taxable profit, and the remaining balance is carried forward as the closing pool value.
Because WDA works on a reducing balance basis, the cash benefit of the allowance is higher in early years and lower later on. A £100,000 main pool balance at 14% produces £14,000 of relief in year one, then £12,040 in year two if there are no new additions or disposals. The pool is never written down in equal chunks unless a small pool allowance or balancing adjustment clears the balance.
A business with a profitable year may prefer to claim AIA or a first-year allowance to accelerate relief. A business with low taxable profits may decide to claim only part of an upfront allowance and carry more value forward into the WDA pool. The right choice depends on your expected profits, Corporation Tax or Income Tax rate, group AIA availability, financing structure and whether the asset is eligible for other reliefs.
Accounting depreciation reflects how the asset is consumed in the business. It helps present a fair view of profit and net book value. WDA is used for tax relief. An asset can be depreciated over five years in the accounts while receiving AIA in year one for tax, or it can be depreciated straight-line while being relieved at 14% reducing balance in the tax computation. This is why your accounts and tax written down value often do not match.
Use this quick guide before choosing the right tab in the calculator.
For most plant and machinery that does not go into the special rate pool or a single asset pool. The rate was 18% before the April 2026 change.
For integral features, long-life assets, solar panels, thermal insulation added to buildings and relevant higher-emission cars.
AIA can usually relieve up to £1 million of qualifying plant and machinery in the period of purchase, but cars are excluded.
From 1 January 2026, a 40% FYA applies to certain new main-rate plant and machinery where conditions are met. Cars and second-hand assets are excluded.
| Asset or Situation | Typical Pool / Treatment | 2026 Rate or Note |
|---|---|---|
| Office equipment, tools, standard machinery | Main pool unless AIA/FYA/full expensing used | 14% WDA on reducing balance |
| Integral features such as lighting, heating and lifts | Special rate pool | 6% WDA |
| Long-life assets over the threshold | Special rate pool | 6% WDA |
| Cars with CO₂ over the relevant threshold | Special rate pool | 6% WDA, with emissions rules checked by purchase date |
| Short-life assets election | Single asset pool | Main rate WDA, with balancing adjustment when disposed |
| Items used partly outside business by sole traders/partners | Separate pool | WDA restricted for private use |
Follow these four steps to build a clear tax relief projection.
Choose main pool, special rate pool, hybrid rate or custom rate based on the asset type and accounting period.
Use the tax written down value from your last tax computation, not the accounting net book value.
Include additions that were not relieved upfront and disposal proceeds for assets removed from the pool.
Multiply the allowance by your tax rate to estimate the cash impact on Corporation Tax or Income Tax.
The best allowance depends on asset type, timing, profit level and eligibility.
These errors can overstate relief, understate relief or create problems during an HMRC review.
| Mistake | Why it matters | Better approach |
|---|---|---|
| Using accounting NBV as the tax pool value | Net book value and tax written down value often differ because depreciation and capital allowances follow different rules. | Use the closing pool balance from the last tax computation. |
| Putting special rate items in the main pool | This can overclaim relief by using 14% instead of 6%. | Check integral features, long-life assets, solar panels and car emissions carefully. |
| Forgetting hybrid-rate periods | A period crossing April 2026 may not use a full 18% or full 14% rate. | Calculate a blended rate based on the days before and after the change. |
| Ignoring private use | Sole traders and partnerships may need separate pools and private-use restrictions. | Keep business-use records and restrict allowances where required. |
| Claiming WDA when AIA would be better | WDA spreads relief over years, while AIA may give immediate relief. | Compare tax savings before finalising the claim. |
This example shows why a Writing Down Allowance schedule is useful for planning cash flow and tax relief.
Assume a limited company starts its 2026 accounting period with a main pool tax written down value of £80,000. During the year it buys £30,000 of eligible machinery, but the directors decide to use available AIA on only £10,000 because profits are expected to be low. The remaining £20,000 is added to the main pool. The business also sells an old machine and receives £5,000 of disposal proceeds. The Year 1 WDA base is therefore £95,000: opening pool of £80,000, plus £20,000 of additions, less £5,000 of disposals.
At the 14% main pool rate, the Year 1 Writing Down Allowance is £13,300. If the company pays Corporation Tax at 25%, the estimated cash tax saving from that allowance is £3,325. The pool carried forward becomes £81,700. In Year 2, if there are no further additions or disposals, the 14% WDA is calculated on £81,700, not on the original cost of the assets. This is the reducing balance effect: relief continues for many years but becomes smaller as the pool is written down.
The same logic applies to the special rate pool, but at 6% the relief is much slower. A £95,000 special rate pool would produce only £5,700 of WDA in the first year before tax rate effects. For long-life assets, integral features and high-emission cars, that slower relief can materially affect investment decisions. Businesses often compare the after-tax cost of buying, leasing and delaying expenditure before committing to large projects.
Good records make your Writing Down Allowance claim easier to support if HMRC asks questions later.
The standard rates are enough for most users, but some periods and planning exercises need a blended or custom percentage.
A custom WDA rate is useful when your accounting period does not fit neatly into a single tax year, when a rate changes part way through the period, or when you are running an internal forecast rather than preparing a formal return. For the 2026 main rate change, a business with a 31 December 2026 year end will have part of the year before the Corporation Tax change date and part after it. Instead of applying 18% or 14% to the full period, the business works out a blended rate based on the number of days in each part of the period.
Custom rates are also helpful for sensitivity testing. For example, you might compare a 14% main pool WDA projection with an upfront AIA claim, a 40% first-year allowance claim, or a finance lease scenario where rental deductions replace ownership allowances. The result is not simply a bigger or smaller deduction: it changes timing, cash flow and the future tax written down value left in the pool.
For important decisions, do not rely only on one rate. Run at least two scenarios: one using the relief you expect to claim, and another using a more conservative assumption. That gives you a range of possible tax savings and helps you avoid overstating short-term cash flow. If the asset is expensive, unusual, partly private-use, leased, imported or linked to property fixtures, professional advice is normally worthwhile.
Use these related pages to build a complete depreciation and tax planning workflow.
Answers to common questions about WDA, tax pools, allowances and 2026 rate changes.