What goes in box 315?
Think of the first pages of the CT600 as streams running into one river. Your trading profit flows in through one set of boxes, rental profit from any property through another, and bank interest through a third. They all meet at box 235, the total before deductions. The form then takes off any deductions and reliefs your company claims, and after box 300 it takes off one more thing: donations your company made to charity. Whatever is left is box 315, your taxable total profits.
Here is a small company's year in numbers:
- Trading profit for tax: £38,000
- Bank interest: £250
- Rental profit on a small unit the company lets out: £6,000
- All the income together: £44,250
- No other deductions or reliefs this year, so that total carries straight through
- Charity donation made during the year: £750
- Box 315: £44,250 minus £750 = £43,500
That £43,500 is what the tax is charged on. At the small profits rate of 19%, the bill on it would be £8,265.
There are also two group relief boxes just above box 315, which only matter if your company is part of a group of companies. If that is you, an accountant is genuinely the right choice, and this guide stays out of it.
One small detail: box 315 takes whole pounds only. On HMRC's printed form the pence are already filled in as 00. Pence only reappear much further down the form, when the actual tax bill is worked out.
Why does box 315 matter so much?
Because it decides which tax rate your company pays. If your company's profit is £50,000 or less, you pay the small profits rate of 19%. Above £250,000 you pay the main rate of 25%. In between, the rate slides gradually from one to the other, through something called Marginal Relief. So box 315 is the number that picks your rate. One wrinkle: those £50,000 and £250,000 markers shrink if your accounting period is shorter than a year, or if your company has associated companies.
What usually goes wrong?
The most common surprise is that box 315 does not match the profit in your accounts. It is not supposed to. By the time the form reaches box 315, costs HMRC does not accept for tax, like depreciation, have been put back on top of your profit, HMRC's own allowances for equipment have been taken off instead, and income like rent and interest has been counted in its own boxes. A gap between your accounts profit and box 315 is normal.
The second trap is charity donations. A donation to charity that is not already counted as a day-to-day business expense comes off at its own box, just before box 315. Take it off in both places and you have counted it twice, which understates your taxable profit. Forget it entirely and you pay tax you did not owe.
The third is simple arithmetic: box 315 must be box 300 minus the donations and group relief boxes, nothing else. Filing software does the subtraction for you; if the numbers do not tie up when you check, something upstream is wrong, not box 315 itself.
Do I have to work this out myself?
No. Filing software fills in box 315 automatically from the earlier boxes; your job is to check the figure looks sensible for the year your company actually had. SimpleReturns builds it from your company's bank statement and a few plain-English questions: your trading profit, rent and interest each land in the right box, donations come off in the right place, and you see the whole 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.