Key takeaway: The main rate writing down allowance (WDA) for plant and machinery pools has been cut from 18% to 24% effective 1 April 2026 for companies and 6 April 2026 for unincorporated businesses — reducing the annual tax relief available on plant and machinery that cannot access accelerated first-year relief. A new 40% first-year allowance partially offsets the cut for qualifying new investment. For practices managing capital-intensive clients, understanding the full capital allowances landscape in 2026 is essential for correct corporation tax computations and sound investment advice.
Capital allowances are often treated as a mechanical part of the corporation tax computation — a set of numbers that the software handles and accountants review. The April 2026 changes are a reminder that capital allowances strategy genuinely matters. The combination of the WDA rate cut, the existing Annual Investment Allowance (AIA) at £1 million, full expensing for companies, and the new 40% first-year allowance creates a more complex decision framework than many clients realise — and getting it right can make a material difference to the timing of tax relief and, therefore, to cash flow.
What Has Changed and Why It Matters
The Autumn Budget 2025 announced that the main rate writing down allowance — which applies to the plant and machinery main pool and special rate pool where expenditure is not covered by other reliefs — would be reduced from 18% to 14% for the main pool (and from 6% to a corresponding lower rate for the special rate pool) from April 2026. This applies to all qualifying expenditure sitting in the pool at the start of the period, as well as new additions during the period that are not covered by accelerated relief.
The practical effect is that businesses with large brought-forward plant and machinery pools — manufacturing businesses, transport operators, rental businesses with significant equipment — will see slower tax relief on those balances going forward. A company with a £500,000 main pool at the start of 2026/27 would previously have claimed £90,000 of WDAs (18%); under the new rate, the claim is £70,000 (14%). The £20,000 difference carries forward in the pool rather than being deducted in the current year. Over time, the full relief is received — but later, and with the time-value cost that deferred relief always carries.
The reduction affects approximately 650,000 businesses that have qualifying expenditure not covered by accelerated allowances. For practices with manufacturing, fleet-heavy, or equipment-intensive clients, this is a meaningful change.
The Offsetting Measures: AIA, Full Expensing, and the New 40% FYA
The rate cut does not change the availability of accelerated allowances that prevent expenditure from entering the pool in the first place:
Annual Investment Allowance. The AIA provides 100% first-year relief on up to £1 million of qualifying plant and machinery expenditure per year. For the vast majority of SME clients, new capital investment will be fully covered by the AIA — meaning it never enters the pool and the WDA rate reduction is irrelevant for new expenditure. The AIA is available to both companies and unincorporated businesses.
Full expensing. For companies (not unincorporated businesses), full expensing provides 100% first-year relief on new main pool plant and machinery expenditure without limit. This was made permanent in the Autumn Statement 2023. For large companies whose capital expenditure exceeds the AIA, full expensing removes the need to pool new main rate expenditure entirely.
New 40% first-year allowance. From 1 January 2026, a new 40% first-year allowance applies to qualifying main rate expenditure in circumstances where other first-year allowances are not available — specifically for assets bought for leasing (which are excluded from full expensing) and by unincorporated businesses (which cannot use full expensing). This partially offsets the WDA reduction for those categories of expenditure.
The result of these measures together is that for most SME clients making new capital investment, the tax treatment of new expenditure is unchanged or improved. The WDA rate cut primarily affects the speed of relief on expenditure already sitting in pools from prior years, and new main rate expenditure that cannot access full expensing or the AIA.
Hybrid Rates for Straddle Periods
For companies and businesses whose accounting period straddles the April 2026 rate change date, a hybrid WDA rate applies. The hybrid is calculated proportionally: the proportion of the accounting period falling before the change date attracts the old rate (18%), and the proportion after attracts the new rate (14%).
For example, a company with a 30 September 2026 year end has six months at 18% and six months at 14%, producing a hybrid WDA rate of approximately 16% for the period. This needs to be calculated correctly for each affected client — applying the wrong rate to the pool will produce an incorrect tax computation.
BrightTax handles the hybrid rate calculation for straddle-period clients automatically, applying the correct proportional rate to the main pool WDA based on the company’s accounting period and the change dates. This removes the manual calculation risk in corporation tax computations for the 2026 filing cycle — a cycle where many practices will be processing straddle-period clients for the first time.
Investment Planning Conversations with Clients
The combined capital allowances landscape creates a clear framework for client advice on investment timing and structuring:
For SME companies planning new plant and machinery investment, the AIA and full expensing mean the WDA reduction is largely irrelevant — new investment should qualify for immediate 100% relief regardless of the pool rate. The planning question is whether expenditure qualifies for full expensing or only for the AIA, and whether the AIA limit creates a timing consideration where investment is spread across financial years to maximise annual relief.
For unincorporated businesses, full expensing is not available but the AIA and the new 40% FYA provide substantial acceleration. For investment above the AIA limit, the 40% FYA on the balance provides materially better relief than the 14% WDA in the year of purchase.
For businesses with large brought-forward pools — particularly those whose prior-year computations included assumptions about future WDA rates — a review of the cash flow timing of tax relief is appropriate. The deferred tax liability effect of slower WDA may be worth quantifying for businesses making significant investment decisions.
Frequently Asked Questions
What is the main rate writing down allowance from April 2026?
The main rate WDA for plant and machinery pools has been reduced from 18% to 14% effective 1 April 2026 for companies and 6 April 2026 for unincorporated businesses. The reduction applies to the annual writing down allowance on the balance of the main pool — both brought-forward balances and new additions not covered by first-year reliefs.
Does the WDA reduction affect clients who use the Annual Investment Allowance?
Not directly, because expenditure claimed under the AIA is deducted in full in the year of purchase and does not enter the pool. The WDA rate reduction affects expenditure that is pooled — either because it exceeds the AIA limit, is in the special rate pool, or is in a long-life asset pool. For most SME clients whose annual capital investment is below £1 million, the AIA means new expenditure is fully relieved regardless of the pool rate.
What is the new 40% first-year allowance introduced from January 2026?
A new 40% first-year allowance applies to qualifying main rate plant and machinery expenditure from 1 January 2026 in cases where other first-year allowances are not available. Its primary beneficiaries are businesses acquiring assets for leasing (excluded from full expensing) and unincorporated businesses (which cannot use full expensing). The 40% FYA provides materially better first-year relief than the 14% WDA for expenditure above the AIA limit.
How does the hybrid rate apply for accounting periods straddling April 2026?
For companies and businesses with accounting periods that straddle the 1 April 2026 (for companies) or 6 April 2026 (for unincorporated businesses) change date, a hybrid WDA rate applies. The hybrid is calculated by weighting the old 18% rate for the portion of the period before the change date and the new 14% rate for the portion after. For example, a 31 December 2026 year end results in approximately nine months at 14% and three months at 18%.
What is full expensing and does it still apply after the WDA change?
Full expensing provides 100% first-year relief on new main pool plant and machinery for companies, with no upper limit. It was made permanent from 1 April 2023 and is unaffected by the WDA rate reduction. Full expensing means that for companies making new qualifying capital investment, no expenditure needs to enter the main pool — the full cost is relieved in the year of purchase. It is not available to sole traders or partnerships.
BrightTax handles capital allowances computations for corporation tax and income tax returns — including WDA calculations, AIA claims, full expensing, and the hybrid rate for straddle-period clients affected by the April 2026 rate change. Find out more about BrightTax or speak to your account manager.
