The Companies House Filing Calendar: When Britain's 5.5 Million Companies Actually Submit — and the Peak-Month Penalty Risk Map

The Register Has a Pulse

Companies House processed 4.2 million sets of annual accounts in the 2024/25 filing year. They did not arrive at a steady 350,000 per month. They arrived in waves — a September surge, a December cliff, a March scramble — because the UK's 5.5 million companies do not share an accounting reference date, but they cluster around predictable anchor points.

The filing calendar is not an administrative footnote. It determines when Companies House enforcement resources are stretched thinnest, when the late-filing penalty pipeline is fed, and when a director's compliance record is most likely to acquire a blemish that credit-reference agencies and potential counter-parties can see.

This article maps that calendar — the statutory framework, the data on actual filing patterns, and the risk concentrations that arise from the interaction of the two-speed deadline system with the April 2025 audit exemption threshold changes.

The Two-Speed Deadline Architecture

UK companies do not all file on the same timetable. The Companies Act 2006 draws a bright line between private and public companies, and that line has two dimensions: the deadline length and what kicks in when you miss it.

Private Companies: 9 Months From the Accounting Reference Date

Section 442(2)(a) of the Companies Act 2006 gives a private company nine months from its accounting reference date (ARD) to deliver its accounts to the Registrar. For a private company with a 31 December year-end, that means 30 September. For a 31 March year-end — the most common ARD among UK companies — the deadline is 31 December.

The nine-month window is a single fixed period. It does not reset if the company changes its year-end. An AA01 shortening the period by one day can, counterintuitively, extend the filing deadline by up to three months for the preceding period — a feature we examined in an earlier piece — but for the period being shortened, the clock is nine months from the new ARD.

Public Companies: 6 Months From the Accounting Reference Date

Section 442(2)(b) gives a public limited company (PLC) six months. The same 31 December ARD that gives a private company until the following September gives a PLC until 30 June. This tighter timetable reflects the public-interest dimension: PLCs have wider share ownership, and their accounts inform market pricing.

The six-month clock applies whether or not the PLC is traded. An unlisted PLC — and there are roughly 8,000 of them, as we have previously covered — gets no dispensation. The legal form, not the trading status, determines the deadline.

The Comparison at a Glance

The private/public distinction in the filing obligation is one of the few areas of UK company law where the legal form carries an unqualified burden. A PLC cannot shrink its filing obligation by shrinking its balance sheet.

The Confirmation Statement Runs on Its Own Clock

Accounts are not the only recurring filing. Under section 853A of the Companies Act 2006, every company must deliver a confirmation statement (form CS01) at least once every 12 months. The review period runs from the company's statement date, which is either the anniversary of incorporation (for the first CS01) or the anniversary of the last statement date.

The confirmation statement and the accounts filing operate on independent cycles. A company with a 31 March ARD and a 15 June statement date files accounts by 31 December and its CS01 by 15 July. The two deadlines can fall in the same month, or six months apart. When they converge, the compliance workload doubles for the same period, and missed deadlines cascade.

The ECCTA reforms added two new contents to the CS01 from March 2024: a lawful-purpose statement (confirming the company's intended future activities are lawful) and a registered email address. A confirmation statement that omits either is incomplete and does not satisfy the section 853A duty.

The Filing Calendar by Volume

Companies House does not publish a monthly filing volume series as a standing statistical release, but the data can be triangulated from three sources: the monthly incorporation statistics (published), the quarterly enforcement outcomes (published in the Registrar's annual report), and the filing receipt pattern observable through the Companies House API's transaction log.

The pattern that emerges is consistent across years:

1. January: Moderate. Companies with a 31 March ARD have filed in December; those with a 30 April ARD are not yet due. Incorporation-season companies — the January registrants from prior years — file confirmation statements.

2. February–March: Low. The quietest filing months. Few ARDs fall in May or June, so few nine-month deadlines land here. Companies House enforcement teams typically run compliance campaigns during this window.

3. April: Moderate, rising. 31 July ARDs trigger 30 April private-company deadlines. The tail-end of the December ARD cohort (those filing at the limit) also lands here with penalties already accruing.

4. May–June: Moderate. 31 August and 30 September ARD cohorts land. PLCs with 31 December ARDs face their 30 June deadline — the single largest PLC filing concentration.

5. July–August: Low. Summer lull. Companies House processing times lengthen slightly as staffing thins, but the inbound volume is seasonally light.

6. September: High. The 31 December ARD cohort — the single largest block of UK companies — reaches its nine-month deadline on 30 September. This is consistently the busiest filing month. Companies House typically processes over 450,000 accounts in September alone.

7. October: High, but falling. Late filers from the September peak flow in, now carrying penalties. The 31 January ARD cohort files by 31 October.

8. November: Moderate. 28 February ARD cohort files by 30 November.

9. December: Very high. The 31 March ARD cohort — the second-largest block — files by 31 December. This is the other seasonal peak, amplified by the calendar-year-end effect: many directors treat 31 December as a psychological compliance deadline even when it is not their statutory one.

The twin peaks — September and December — account for roughly 40% of annual accounts filings between them. The September peak is larger in absolute volume; the December peak is more compressed, because the 31 March cohort includes a higher proportion of small companies whose directors leave filing to the final weeks.

The April 2025 Threshold Uplift and the Filing Map

The Companies (Accounts and Reports) (Amendment) Regulations 2024, effective for financial years beginning on or after 1 April 2025, raised the qualifying thresholds for the small-company regime and the micro-entity regime. The turnover threshold for a small company moved from £10.2 million to £15 million; the balance-sheet total threshold from £5.1 million to £7.5 million.

The immediate filing-calendar effect is counterintuitive: it reduces, not increases, the compliance burden for companies that cross the threshold. Companies that would previously have been medium-sized — and therefore required to file full accounts, including a profit-and-loss account and a directors' report — now qualify as small. Small companies can file abridged accounts under section 444, and, critically, the P&L does not appear on the public register for small companies that take the section 444 option (until ECCTA's full P&L mandate comes into force, which is a separate and still-impending reform).

The larger effect is on audit. The audit exemption thresholds now align with the small-company thresholds. A company with turnover below £15 million and a balance-sheet total below £7.5 million and fewer than 50 employees is exempt from statutory audit — provided it is not a PLC, a regulated entity, or part of an ineligible group. The pool of companies that must commission an audit before filing shrank materially in April 2025, which should — over the 2026 filing cycle — reduce the tail of late filers who are delayed waiting for audit completion.

The Penalty Clock: Automatic, Escalating, and Unforgiving

The late-filing penalty regime under section 453 is automatic. There is no discretion at the point of imposition. If the accounts are not delivered by midnight on the deadline day, the penalty is generated by the system. The amounts for private companies are:

For a private company that files its accounts more than six months late for a second consecutive year, the penalties double under section 453(4A): £300 / £750 / £1,500 / £3,000. The doubling applies per-filing, not per-company — it is the second consecutive late filing that triggers it, not the second year of the company's existence.

The penalty is civil, not criminal. It is registered as a debt to the Crown and Companies House pursues it through the county court if unpaid. The penalty does not replace the obligation to file: even after paying £1,500 in penalties, the company must still deliver its accounts. And the Registrar can strike off a company that fails to file, penalty or no penalty.

The practical risk concentrates in the final weeks before the deadline. Companies House data shows that approximately 30% of accounts in the September and December peaks are filed in the last seven days of the deadline month. A technical failure, an authentication error on the WebFiling portal, or an IXBRL tagging rejection in that final week leaves no buffer. The penalty is automatic even if the filing was attempted but rejected — the system records the date of successful delivery, not the date of first attempt.

Month-by-Month Risk Calendar

For a director or company secretary managing a portfolio of companies, the following calendar maps the practical risk points across the filing year:

• January: Low inbound risk. Good month to audit internal compliance calendars for the year ahead. Check that ARDs are correctly recorded on the register — an error here cascades into every deadline.
• February: Confirm confirmation-statement dates. If any CS01 is overdue, file it now. An overdue CS01 does not trigger automatic civil penalties in the same way as accounts, but it is a criminal offence under section 853L and can ground a strike-off.
• March: The 31 March ARD cohort enters its final quarter. If you have a 31 March ARD and are not yet preparing accounts, you are behind schedule.
• April: First penalty notices from the 30 September cohort (six months late) land. These are the £1,500 letters for private companies. PLCs with 30 September ARDs face their deadline.
• May: The 30 June PLC deadline approaches. Listed companies with 31 December ARDs are in their final month. Confirm that the audit is on track.
• June: 30 June deadline for PLCs with 31 December ARDs. 31 July ARD private companies enter their final quarter.
• July: 31 October ARD cohort enters its final quarter. Summer lull in inbound filings.
• August: The calm before September. Use this month to prepare accounts for the 31 December ARD cohort.
• September: Peak month. 30 September deadline for private companies with 31 December ARDs. The largest single filing event of the year. Do not file on 29 September and assume it will be processed same-day.
• October: Late filers from September begin receiving £150 penalties. The clock for escalation to £375 begins. 30 November ARD cohort enters its final stretch.
• November: Second-order peak. 31 January ARD cohort enters its final quarter.
• December: 31 December deadline for the 31 March ARD cohort. The compressed year-end peak. Companies House typically closes the WebFiling portal for maintenance on Christmas Day; the deadline is not extended for the holiday.

ECCTA and the Filing Future

The Economic Crime and Corporate Transparency Act 2023 does not change the deadline architecture directly — sections 442 and 853A remain as they were — but it changes what must be filed and who can file it.

Three ECCTA-driven changes interact with the filing calendar:

1. Identity verification for directors and PSCs. Once the identity-verification regime commences (expected in phases through 2026), a director whose identity has not been verified will be unable to file accounts or confirmation statements. A filing attempted by an unverified director will be rejected. For companies with a single director — approximately 2.3 million of the 5.5 million on the register — a verification gap on 29 September means a missed deadline with no remedy.

2. The end of the paper-filing option for accounts. ECCTA empowers the Registrar to mandate software-only filing for all accounts. The transition timetable has not been finalised, but once it takes effect, the paper form AA02 (dormant company accounts) will no longer be accepted. Dormant companies — approximately 1.2 million of them — will need to file through software or the WebFiling service. For directors who have historically posted a paper AA02, the behavioural change is material and the risk of missed deadlines in the first software-only cycle is real.

3. Authorised Corporate Service Providers (ACSPs) as the filing gate. As the ACSP regime matures, an increasing share of filings will be routed through regulated intermediaries rather than filed directly by company officers. This should improve compliance timeliness — ACSPs have professional systems and calendar management — but it also introduces a single-point-of-failure risk: an ACSP's IT outage in the last week of September could affect hundreds of client companies simultaneously.

What a Director Should Do Now

The filing calendar is fixed. The deadlines are statutory. The penalties are automatic. The only variable a director controls is when the work starts.

Three practical steps:

1. Pull your ARD from the Companies House register today — not from your internal records. If the register shows a different ARD from what you believe to be correct, the register governs. A mismatch means you are either filing late or filing for the wrong period.

2. Map the nine-month (or six-month) clock from that ARD and count backwards six weeks. That earlier date — not the deadline — is your practical completion target. Accounts that are ready six weeks before the deadline can survive an IXBRL rejection, an audit delay, or a director-identity verification gap.

3. Check whether the April 2025 threshold changes affect you. If you now qualify as small or micro, your filing obligation is lighter and faster to discharge. If you have moved out of the audit-exempt pool, your filing timeline just got materially longer — plan the audit into the calendar, not around it.

The Companies House filing year has a rhythm. The companies that miss it are overwhelmingly those that did not know the tune.