If your limited company’s accounting reference date is 31 December 2025, your statutory accounts are due at Companies House by 30 September 2026 — nine months after the year end. That’s roughly six weeks away, which makes now the right moment to check where things actually stand, rather than in the last fortnight of September when accountants get busiest and options narrow fastest.

Companies House does not grant automatic extensions. The only route to more time is a formal application citing genuinely exceptional circumstances entirely outside your control, and it needs to be made before the deadline, not after you’ve already missed it. Miss the date without one, and the penalty is automatic — no warning letter, no grace period.

Why this deadline catches SMEs out

Part of the problem is that this deadline sits alongside two other dates that are easy to conflate. Corporation tax has to be paid nine months and one day after your accounting period ends — before your Companies House filing is even due — and your CT600 corporation tax return isn’t due until twelve months after the year end. Three different obligations, three different deadlines, all counting from the same year-end date but landing at different points. It’s a common and expensive mistake to file accounts on time and assume the tax position is settled too.

The other change worth knowing about: the joint HMRC and Companies House free filing service closed permanently on 31 March 2026. If your business has filed accounts and tax returns through that portal in previous years, you now need commercial accounting software to file, and you should already have downloaded and saved at least the last three years of your previously filed returns — that historical access disappeared along with the service itself. If you haven’t done that yet, do it before you file this year’s accounts, while you can still confirm what your prior submissions looked like.

Your six-week checklist

Confirm your actual accounting reference date. Don’t assume — check Companies House’s own record for your company, since reference dates can shift if you’ve changed your year end in the past, and the deadline calculation depends entirely on getting this right.

Check your commercial filing software is set up and tested, not just purchased. With the free joint service gone, a filing that used to be a formality now depends on a third-party tool working correctly on the day you need it.

Archive your last three years of filed accounts and returns now, before you’re focused entirely on this year’s submission. If you want that handled properly rather than as a rushed afterthought, Archive.Partners specialises in exactly this kind of business record-keeping and retention.

If your accounts involve anything contractually sensitive — shareholder agreements, related-party transactions, terms that need to be reflected accurately — it’s worth having your underlying legal documentation in order alongside your accounts. Smallprint provides UK legal document templates that can help you tidy that up before your accountant needs it.

The takeaway

Thirty September isn’t a soft deadline, and this year it arrives without the safety net of a free government filing portal to fall back on if your usual process breaks down. Confirm your reference date, test your filing software now, and get your historical records archived properly — six weeks is enough time to do this calmly, but not if you leave it to the last week.