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What is box 155 on the CT600? (trading profits)

Reviewed by Lee Jones, Founder · Updated 16 July 2026
The short answer

Box 155 is your company's trading profit worked out for tax, not the profit printed in your accounts. HMRC's own label for it is "Trading profits". It starts from your accounts profit, adds back costs the taxman does not accept (like depreciation and client entertaining), and swaps in HMRC's own allowances for equipment you bought. So it is normal, and usually correct, for box 155 to be a different number from your accounts.

Official source. This guide is a plain-English summary of official GOV.UK guidance, not advice. The authoritative source is The Company Tax Return guide on gov.uk. Always rely on that over our summary.

What goes in box 155?

Your accounts show one version of profit: money in, minus money out. Box 155 asks for a second version: the profit HMRC taxes. Gov.uk says it plainly: the profit for Corporation Tax "is different from the profit or loss shown in your annual accounts".

Getting from one to the other takes three steps:

  1. Start with the profit in your accounts. Say your company made £40,000.
  2. Add back the costs HMRC does not allow. Some things reduce your accounts profit but are not allowed against tax. The two you are most likely to have are depreciation (the yearly write down of your equipment's value) and entertaining clients. Say that is £3,000 of depreciation and £500 of client meals: your running total is now £43,500.
  3. Take off capital allowances. Instead of depreciation, HMRC gives you its own deduction for things like equipment, machinery and business vehicles. Most small companies can deduct the full cost of that kind of kit in the year they buy it, up to £1 million a year. Say you bought £4,000 of laptops and office kit: £43,500 minus £4,000 = £39,500.

That final £39,500 is your box 155 figure. It is close to the accounts profit of £40,000 but not equal to it, and that gap is the whole point of the box.

One more thing box 155 does not do: losses from earlier years do not get taken off here. They go in the next box down, box 160, and the form does the subtraction to reach box 165, your net trading profit.

What usually goes wrong?

The classic mistake is copying the profit figure straight out of your accounts into box 155. If your accounts include depreciation, client entertaining or new equipment, that copied figure is simply the wrong number for tax. It can be too low or too high: too low when the costs HMRC refuses outweigh your capital allowances, and too high when the allowances are bigger, as they were in the example above. Either way, it is not the figure HMRC asked for.

The two add backs to watch:

  • Depreciation. Your accounts spread the cost of equipment over several years by writing a bit off annually. HMRC ignores that number completely. You add every penny of it back, then claim HMRC's capital allowances instead, which for most small purchases means the full cost in the year you bought the item. Often the allowance is bigger than the depreciation, so this swap can actually lower your tax bill.
  • Entertaining clients. Taking a customer to lunch may be good business, but the tax rules do not allow a deduction for entertaining and gifts. It stays in your accounts as a real cost, and gets added back for tax.

The other trap runs the opposite way: forgetting capital allowances entirely. If you bought a van, a computer or tools during the year and never claimed the allowance, your box 155 is higher than it needs to be, and so is your tax bill.

Do I have to work this out myself?

No. Filing software works box 155 out for you; your job is to check it looks sensible. SimpleReturns works it out from your company's bank statement and a few plain-English questions: it sorts every transaction, adds back the disallowed costs like client entertaining, applies the capital allowances for equipment you bought, and shows you the working before anything is sent. It is free to start, no card needed, and filing costs £99 flat, covering both your HMRC return and your Companies House accounts.

If your company is part of a group, or claims research and development relief, this box stops being simple and an accountant is genuinely the right choice.

Common questions

Is box 155 supposed to match the profit in my accounts?

No. It usually will not, and that is fine. Box 155 is the tax version of your profit, and gov.uk itself says the Corporation Tax figure is different from the accounts figure.

My company made a loss. What goes in box 155?

You do not put a minus number in box 155; the box is for profits only. A trading loss is recorded in the losses part of the return instead, and your filing software will put it in the right place.

Where do losses from earlier years go?

Not in box 155. If you have unused trading losses from a previous year, they go in box 160, and the form takes them off your box 155 profit to give the net figure in box 165.

Want box 155 worked out for you?

SimpleReturns works box 155 out from your company's bank statement and a few plain-English questions: it sorts every transaction, adds back the disallowed costs, applies the capital allowances, and shows you the working before anything is sent. Free to start, no card needed, and £99 flat covers both filings.

Start your return

If your company is part of a group, or claims research and development relief, an accountant is genuinely the right choice, and we say so plainly.

General guidance, not advice. This guide explains how the rules generally work for small UK limited companies. It isn't tax advice for your specific situation, if you're unsure, check with us or an accountant.