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What are boxes 780 and 805 on the CT600? (the losses memorandum)

Reviewed by Lee Jones, Founder · Updated 17 July 2026
The short answer

Near the bottom of the CT600 sits a section called "Losses, deficits and excess amounts". Think of it as the form's memory. Box 780 records a trading loss your company made this year; box 805 records a loss from renting out UK property this year. Writing the loss here is how this year's bad news becomes next year's tax relief.

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.

Why does my loss appear twice on the form?

Because the form asks two different questions. The top half asks "how much profit is there to tax this year?", and in a loss year the honest answer is £0, so the trading profit box (box 155) says £0. The bottom section asks "what losses happened this year that might matter later?", and that is where the loss itself is written, in full, in box 780. Nothing is counted twice: the £0 settles this year's bill, and the entry at the bottom lets a future year benefit. Our guide to box 235 covers the top half of that story; this page is the memory at the bottom.

What goes in box 780 and box 805?

Box 780 is for a loss made by your company's trade this year, which for most small companies simply means the business spent more than it earned once the tax rules have adjusted the numbers.

Box 805 is its neighbour for a different kind of loss: money lost renting out UK property. If your company's letting made a loss this year, that loss goes in box 805, not box 780. Every memorandum line works the same way: this year's losses only. The running total carried forward from past years lives in your company's supporting calculations, not in these boxes.

What does a loss year look like, then a good year?

Say your company makes an £8,000 trading loss this year. On this year's return, box 155 says £0 and box 780 says £8,000. There is no Corporation Tax to pay, but the return still has to be filed.

Next year the company recovers and makes a £20,000 profit. If the loss was not used any other way, it carries forward while the trade keeps going, and next year's return brings it in through a different box (box 160). Tax is then worked out on £12,000, not £20,000: at the 19% small profits rate that is £2,280 instead of £3,800, so last year's bad news saved £1,520. The exact route a loss takes can vary, so treat this as the simple everyday case.

What happens if the memorandum is left empty?

Nothing bad happens today, which is exactly why it gets missed. But the claim for a loss forms part of your tax return, and an unrecorded loss cannot quietly turn up years later. You can usually fix a gap by amending the return or writing to HMRC, but only within two years of the end of the loss year. The safe move is to record it now.

One more reminder: a loss year still needs a full return, on time. Miss the deadline and the penalty is £200 from the first day.

Do I have to fill this in myself?

No. SimpleReturns fills in the losses memorandum automatically in a loss year, worked out from your bank statement and a few plain-English questions, and carries the loss forward onto the next year's return so the relief is not forgotten. You review every figure before anything is sent. It is £99 flat, covering both filings: the tax return to HMRC and the accounts to Companies House.

If your company is part of a group sharing losses between companies, an accountant is the right call for that, plainly.

Common questions

The loss already made my profit box £0. Why write it again in box 780?

The £0 settles this year. Box 780 is the record that lets a future year use the loss. Skip it and a later profitable year could pay more tax than it needed to.

Is box 805 where my loss carries forward to next year?

No. Box 805 is only for a loss your company's UK rental business made this year. The carried-forward total sits in your records; next year's return picks it up through its own boxes.

I forgot to record a loss on last year's return. Is it gone?

Usually not, if you act quickly. You can generally amend the return or write to HMRC within two years of the end of the loss year, so sort it sooner rather than later.

Filing a loss year and want the memory kept for you?

SimpleReturns records the losses memorandum automatically, from your bank statement and a few plain-English questions, and carries the loss onto next year's return so the relief is waiting. Free to start, no card needed, £99 flat when you file.

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And if you are sharing losses around a group, we will say plainly that an accountant is the better route.

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.