Every limited company has to prepare annual accounts and deal with corporation tax — there's no opting out, even in a year you made little or nothing. None of it is especially hard for a small company, but there are several deadlines, they're owed to two different bodies, and one of them is arranged in a way that catches people out every single year. This is the financial-filing half of running a company, laid out plainly.
Two things, related but separate
The first thing to untangle is that "the accounts and the tax" are two distinct obligations to two different organisations. Your annual accounts go to Companies House (and to HMRC) and are the financial record of your company's year. Your corporation tax is dealt with through HMRC, who you pay and to whom you file a corporation tax return. They're connected — your accounts feed the calculation of the tax you owe — but they're separate filings on separate deadlines, and treating them as one thing is where the confusion starts. (Both sit alongside your confirmation statement on the wider list of things a company files each year.)
Annual accounts: what you file, and when
Each year you prepare statutory accounts and file them with Companies House. The deadline is nine months after your accounting reference date — your company's financial year-end, which Companies House sets automatically when you incorporate. There's one exception that trips up new companies: your very first set of accounts is due 21 months after the date of incorporation, not nine months after year-end, because the first accounting period is usually longer than a year.
What a small company actually has to file is less than you might fear. Under the current rules, small companies can file a reduced set of accounts — typically a balance sheet without the full profit and loss account — which keeps a lot of financial detail off the public record. Micro-entities can file something simpler still.
Late accounts are the one Companies House filing that carries an automatic financial penalty, and it escalates fast: £150 if you're up to a month late, rising in steps to £1,500 for being more than six months late — and the penalty doubles if you file late two years running. (A dormant company still files accounts too, though a much simpler version.)
Corporation tax: the trap built into the deadlines
Corporation tax is where the genuinely costly mistake lives, and it's worth understanding exactly why. First, registration: you must register for corporation tax within three months of starting to trade. Then there are two annual deadlines — and here's the trap — they fall at different times, in a counter-intuitive order. You have to pay your corporation tax 9 months and 1 day after the end of your accounting period. But you don't have to file your company tax return (the CT600) until 12 months after the end of the period. Read that again: the payment is due three months before the return. Plenty of directors assume, reasonably but wrongly, that you pay when you file — and end up paying late, with interest running from the day after the payment deadline. The fix is simply to calculate and pay the tax by the nine-month-and-a-day point, even though the return itself isn't due yet.
As for the rate, corporation tax is charged at 19% on profits up to £50,000 and 25% on profits above £250,000, with marginal relief tapering between the two thresholds. Most small companies sit at the 19% end.
What's changed recently
A couple of recent developments are worth knowing. From April 2026, HMRC requires company tax returns and the accounts submitted to HMRC to be filed using commercial software — HMRC's old free online filing service has closed. If you file your own corporation tax, this means using approved software rather than the previous free route.
You may also have seen headlines about bigger changes to Companies House accounts filing — mandatory software-only filing, and small companies having to publish full profit and loss accounts, originally planned for April 2027. Those reforms were paused in January 2026 and are currently under review with no set date, so for now the existing rules — including the reduced "filleted" accounts and the Companies House online filing service — still apply. It's worth keeping half an eye on, but there's nothing to act on yet.
Keeping on top of it
The thing that makes all of this manageable is realising that every one of these deadlines flows from a single date: your accounting reference date. Once you know your year-end, your accounts deadline (nine months later), your corporation tax payment date (nine months and a day later), and your CT600 deadline (twelve months later) are all fixed. Mark all three, treat the payment date as the real corporation tax deadline rather than the filing date, and make sure the money to pay it isn't accidentally spent — a common problem when a healthy-looking bank balance is really holding the tax you'll owe. Most of the trouble here isn't the filing; it's being surprised by a date you could have seen coming.
Common questions
- When are my company accounts due?
- Nine months after your accounting reference date (your financial year-end). Your first accounts are an exception — they're due 21 months after incorporation.
- When do I pay corporation tax, and when do I file the return?
- You pay 9 months and 1 day after your accounting period ends, but you file the CT600 return 12 months after period end. The payment comes first — three months before the return is due — which catches a lot of people out.
- What's the corporation tax rate?
- 19% on profits up to £50,000 and 25% on profits over £250,000, with marginal relief in between. Most small companies pay 19%.
- Do I have to use software to file now?
- For corporation tax, yes — since April 2026 HMRC requires commercial software for the CT600 and accounts sent to HMRC, as its free service has closed. Companies House's own proposed software-only rule for accounts was paused in January 2026.