Depreciation in your accounts isn't tax-deductible — capital allowances replace it. You disallow the depreciation charge in the P&L section, then claim allowances on what the company actually spent, in the Assets section of the Corporation Tax screen. For the whole journey from a depreciation charge in the trial balance to the computation, see Depreciation in your trial balance.
Choose your pools
The General tab is the allowance computation itself, organised by pool. Switch on the pools you need — Plant and Machinery covers most equipment; Special Rate is for integral building features and higher-emission cars; there are also pools for energy-efficient machinery and cars, structures and buildings, and ineligible assets. Each selected pool gets a column showing opening balances, additions, disposals, allowances and the carried-forward written-down value.
Record what you bought
On the Fixed Asset Additions tab, click Add Asset and record each purchase: name, date, cost, which pool it belongs to, and whether it was brought into use in the period. The dated list matters — allowance entitlement follows the date the expenditure was incurred, and the additions aggregate automatically into the pool computation on the General tab.
Two first-year allowances give 100% relief and have their own CT600 boxes. Record a new zero-emission car against Energy Efficient Cars (box 726) and electric vehicle charge-points against Electric Vehicle Charge-Point (100% FYA) (box 713). Both are available for expenditure up to 31 March 2027 (extended a year by the 2025 Budget); after that the asset types are no longer offered and a later-dated asset is flagged. For an accounting period beginning on or after 1 April 2026, boxes 726 and 713 are not in use until HMRC updates its online service in April 2027; until then HMRC asks for both claims in box 725 (other allowances).
New main-rate plant and machinery bought on or after 1 January 2026 — including equipment you lease out, which full expensing does not cover — can instead go against Main Rate 40% FYA. Tax Optimiser claims 40% in the year of purchase and adds the other 60% to the main pool from the following period. HMRC adds two CT600 boxes for this allowance in April 2027 (box 696, or box 739 when the allowances belong to a property business). Until then it asks for the claim in box 725, or box 750 for a property business, with the cost in box 760. From 1 April 2026 the main pool writing-down allowance is 14% (was 18%); a period that spans the change gets a time-apportioned rate.
A new electric van or other zero-emission goods vehicle bought before 1 April 2025 goes against Zero-Emission Goods Vehicle (100% FYA) and is reported in box 723. That asset type is only offered for periods starting before 1 April 2025; a new van bought later gets Full Expensing (100%) instead. See Electric vans and zero-emission goods vehicles.
Allocate the Annual Investment Allowance
The AIA Allocation tab shows your AIA entitlement for the period (£1,000,000 a year, apportioned for short or long periods) alongside your plant-and-machinery and special-rate expenditure. Enter how much of each you're claiming as AIA — usually the full amount up to the limit, which gives 100% relief in year one. Anything not covered by AIA stays in the pool for writing-down allowances instead. If you have both main-rate and special-rate spend, allocate AIA to the special-rate pool first — its writing-down rate is lower, so AIA is worth more there.
A group of companies shares a single AIA. If the company is in a group, enter the annual amount allocated to it in Group AIA share at the top of the tab; the entitlement for each date range is then worked out from that share instead of the full £1,000,000.
Brought-forward pools
Enter last period's closing written-down values in Write down allowance B/F on the General tab. When the organisation has an earlier saved computation, the tab shows the main pool and special rate pool it carried forward — click Use as written down allowance B/F to copy them in. At the foot of the General tab, Tax pools and allowances claimed shows each pool's movement for the period (brought forward, additions, AIA, disposals, writing-down allowance, balancing charge, carried forward) and the total allowances claimed, so you can check the claim without opening the computation.
When the trade stops
For the final period of a trade that has permanently ceased, tick Trade ceased in this period at the top of the Assets section. No AIA, first-year allowances or writing-down allowances are due for that period: enter the disposal proceeds (or market value) of every remaining asset, and each pool's remaining balance is claimed as a balancing allowance (a negative balance is a balancing charge). On a return split into two periods, only the second gets the balancing allowance. The same tick lets a final trading loss be carried back three years under terminal loss relief — see Carrying back a trading loss.
Allowances that are not in the trade
Capital allowances claimed by at the top of the Assets section decides which activity the allowances belong to. Trade is the usual choice. Choose UK property business for a letting company’s assets (see UK property income and losses), or Investment business (management expenses) for equipment used to manage a company’s investments — those allowances are relieved in CT600 box 255 alongside its management expenses (see Management expenses for investment companies). Either way the allowances come out of the trading profit and the CT600 analysis moves to boxes 733 to 755, where EV charge-points, zero-emission goods vehicles and zero-emission cars have their own boxes (737, 748 and 751). For an accounting period beginning on or after 1 April 2026, HMRC asks for charge-point and zero-emission car claims in box 750 instead of 737 and 751 until it updates its online service in April 2027.
Where it shows up
The claim flows straight through: the headline payable figure updates, and the computation document gains a full set of fixed-asset schedules — D2 capital allowances summary, D3 annual investment allowance, D4 the main pool movement and D5 the additions analysis — so the numbers you file are fully supported.
On the CT600 the allowances are analysed box by box. Zero-emission cars, EV charge-points and zero-emission goods vehicles are reported in their own boxes (726, 713 and 723) rather than in the main pool figure, as the CT600 Boxes section shows. For an accounting period beginning on or after 1 April 2026, HMRC asks for zero-emission car and charge-point claims in box 725 instead of 726 and 713 until April 2027. Capital allowances on the CT600 explains every box from 688 to 775, with a worked example.
Next: Trading losses.
