Why Are First Company Accounts Sometimes Longer Than 12 Months?

If you have recently incorporated a UK limited company, you may be surprised to discover that your first company accounts can cover more than 12 months. This is normal. For most newly incorporated UK private limited companies, the first accounting period begins on the date of incorporation and ends on the company's first accounting reference date (ARD). Because Companies House normally sets that first ARD as the last day of the month in which the company's incorporation anniversary falls, the first accounting period commonly runs for slightly more than a year.

For example, if a company is incorporated on 11 May 2026, its first accounting reference date will normally be 31 May 2027. Its first accounts therefore cover approximately 12 months and three weeks. This longer first accounting period is deliberate and built into the UK company reporting system. It does not mean the company has made a mistake, nor does it mean that directors can simply choose any period they want.

Understanding how the first accounting period works is important because it affects your Companies House filing deadline, Corporation Tax reporting, bookkeeping and financial planning.

The Short Answer: Why Can First Accounts Exceed 12 Months?

A UK company's first accounting period starts on the day it is incorporated, but its first accounting reference date is normally the last day of the month in which its incorporation anniversary occurs. That creates a first accounting period that is usually longer than exactly 12 months. For example:

The UK system is designed this way so that companies can have a consistent financial year-end without forcing the first financial period to end on the exact anniversary of incorporation. After the first accounting period, subsequent accounting periods are normally 12 months long and end on the company's accounting reference date.

What Is an Accounting Reference Date?

The accounting reference date, or ARD, is the date on which a company's accounting reference period normally ends. For a newly incorporated company, Companies House normally sets the first ARD as the last day of the month in which the anniversary of incorporation falls. Consider three examples:

Company incorporated on 3 January

Its first ARD will normally be 31 January of the following year. The first accounts therefore cover: 3 January → 31 January

Company incorporated on 18 June

Its first ARD will normally be 30 June of the following year. The first accounts cover: 18 June → 30 June.

Company incorporated on 27 November

Its first ARD will normally be 30 November of the following year. The first accounts cover: 27 November → 30 November. The important detail is that the ARD is tied to the month, rather than simply being exactly 12 months after incorporation.

Why Doesn't the First Year Simply End on the Anniversary?

This is where the UK system can seem counterintuitive. Suppose you incorporate a company on 11 May 2026. If the company simply had a 12-month financial year, its first year would end on 10 May 2027. Instead, the normal Companies House arrangement gives the company an accounting reference date of 31 May 2027. That means the first accounting period runs from: 11 May 2026 to 31 May 2027

The result is a first period of approximately 12 months and three weeks. GOV.UK specifically uses this type of example when explaining why first accounts usually cover more than 12 months. This is not an accidental extension. It is a consequence of the statutory accounting reference-date system. Once that first period ends, the company normally moves into regular 12-month accounting periods.

How Long Can a First Accounting Period Be?

A company's first accounting reference period is generally more than six months but no more than 18 months, beginning on incorporation and ending on its accounting reference date. That distinction matters. A first set of accounts being longer than 12 months is normal.

A first accounting period approaching 18 months can also occur, but that is not the same thing as saying every new company automatically gets an 18-month first year. The normal incorporation rules usually produce a period of just over 12 months. A longer period can arise where the accounting reference date has been deliberately changed.

Example of a longer first accounting period

Imagine a company is incorporated on 1 January 2026. Its normal first ARD is 31 January 2027, giving a first accounting period of roughly 13 months. If the company changes its accounting reference date in accordance with Companies House rules, the first period can potentially be extended, subject to the statutory restrictions.

Companies House currently states that an accounting period cannot normally be extended beyond 18 months from its start date, except in specific circumstances such as administration. So there is an important distinction: A first period of more than 12 months is normal. A period approaching 18 months requires a different accounting-date arrangement.

Does a Longer First Accounting Period Mean You Have More Time to File?

Not exactly. This is one of the most common misunderstandings among new directors. For a private company whose first accounts cover more than 12 months, the filing deadline is generally the later of:

• 21 months from the date of incorporation; or
• 3 months from the accounting reference date.

For example, a private company incorporated on 1 January 2025 with a first accounting reference date of 31 January 2026 has until 1 October 2026 to deliver its first accounts to Companies House. So the length of the accounting period and the amount of time available to file are related, but they are not the same calculation. After the first accounting period, a private company normally has 9 months from the end of its accounting reference period to file its annual accounts.

Why This Is Different From Corporation Tax

This is arguably the most important practical point for a new company. Your first Companies House accounts may cover more than 12 months, but your Corporation Tax accounting period cannot exceed 12 months. That means your first set of statutory accounts and your first Corporation Tax reporting periods can be different. For example, suppose:

• Company incorporated: 11 May 2026
• First ARD: 31 May 2027
• First accounts: 11 May 2026 – 31 May 2027

The Companies House accounts cover more than 12 months. However, Corporation Tax may need to be divided into two accounting periods because a Corporation Tax accounting period cannot be longer than 12 months. GOV.UK confirms that a company may therefore need to file two Company Tax Returns covering the period represented by its first accounts. This catches many first-time directors by surprise.

The key distinction

Companies House:
First accounts can cover more than 12 months.

HMRC Corporation Tax:
A Corporation Tax accounting period cannot exceed 12 months. As a result, your company's first statutory accounts and its first tax returns may not line up perfectly.

Why the Difference Matters to Startups

Imagine a technology startup incorporated in January but launched commercially in April. The founder might think: “My first accounts cover January to February next year, so I don't need to worry about tax reporting until then.” That could be wrong. The company may have Corporation Tax obligations based on when it began trading and its Corporation Tax accounting periods, even though its first Companies House accounts have a later filing deadline.

This is why founders should treat Companies House compliance and HMRC compliance as two connected but separate systems. For businesses using accountants, this distinction is usually built into the annual compliance process. For founders handling their own administration, it is particularly important not to rely on one filing deadline as a proxy for all the others.

Does the Company Need to Be Trading for the First Accounts to Cover More Than 12 Months?

No. The length of the first Companies House accounting period is primarily connected to incorporation and the accounting reference date, not simply to when the company starts trading. A company could be incorporated in January, remain dormant for several months and begin trading later. Its Companies House accounting period can still run from the incorporation date to its first ARD.

However, its tax obligations can depend on when it becomes active for Corporation Tax purposes. GOV.UK distinguishes between companies that begin trading when they are incorporated and companies that start trading later, because the tax reporting dates can differ. This is particularly relevant to founders who incorporate a UK company well before launching a business.

Can You Choose a Different Year-End?

Yes. A company can change its accounting reference date, subject to Companies House rules. Changing the ARD effectively changes the company's financial year-end. A company might want to do this to align its year-end with:

• a parent company's reporting year
• a group company's financial year
• an investor reporting cycle
• an international business structure
• a commercially convenient period

Companies House allows companies to change their current or immediately previous accounting reference date, provided the relevant requirements are met. However, changing the date is not something directors should do casually. The new accounting period needs to be calculated correctly, and there are restrictions on extending periods.

Important: You cannot simply add months whenever you want

Companies House specifically warns against simply adding six months to an accounting period. An extension cannot normally create an accounting period longer than 18 months from its start date, unless a specific exception applies.

There are also restrictions on repeatedly extending accounting periods. And if your accounts are already overdue, changing the accounting reference date is too late to solve the overdue filing problem.

Why Some Founders Deliberately Choose a Different Year-End

Although the default ARD works perfectly well for many businesses, there can be commercial reasons for choosing a different financial year-end. For example, a UK subsidiary of an overseas group may want its financial reporting to align with the parent company's reporting calendar. A seasonal business might also prefer a year-end immediately after its busiest trading period, when stock levels and operational activity are easier to assess.

The right year-end therefore isn't always the one automatically assigned by Companies House. However, founders should consider the accounting, tax and administrative consequences before changing it. For international businesses, this becomes particularly relevant where UK accounts need to feed into group reporting in another jurisdiction.

What Happens After the First Accounts?

Once the first accounting reference period ends, the company's reporting cycle becomes much easier to predict. For most private companies:

First period:
Incorporation → first accounting reference date

Subsequent periods:
Accounting reference date → same accounting reference date the following year, For example:

First period:
11 May 2026 → 31 May 2027

Second period:
1 June 2027 → 31 May 2028

Third period:
1 June 2028 → 31 May 2029

And so on. This is why the first set of accounts can feel unusual while later accounting periods settle into a conventional 12-month cycle. GOV.UK confirms that subsequent accounting periods normally cover the company's financial year from one ARD to the next.

What Should a New Company Do?

The simplest way to avoid confusion is to establish your compliance calendar immediately after incorporation.

Check these five dates

1. Incorporation date — when the company legally came into existence.
2. Accounting reference date — when the Companies House accounting period normally ends.
3. First accounts filing deadline — generally 21 months from incorporation or 3 months from the ARD, whichever is later, where the first accounts exceed 12 months.
4. Corporation Tax accounting period — which cannot exceed 12 months.
5. Company Tax Return and Corporation Tax payment deadlines — separate HMRC obligations.

Also remember that your company may have other filing obligations, such as confirmation statements, VAT returns or PAYE reporting, depending on its circumstances.

Common Mistakes to Avoid

Mistake 1: Assuming the first accounts must cover exactly 12 months

They usually do not.

Mistake 2: Assuming the first accounts deadline is 12 months after incorporation

For a typical private company whose first accounts cover more than 12 months, the Companies House filing period is generally much longer.

Mistake 3: Treating the Companies House deadline as the tax deadline

Your HMRC Corporation Tax periods follow different rules.

Mistake 4: Assuming a dormant company has no compliance obligations

Dormant companies can still have Companies House filing requirements.

Mistake 5: Changing the year-end without checking the consequences

An accounting reference date change affects the accounting period and potentially the filing timetable.

Mistake 6: Waiting until the filing deadline to prepare accounts

Your accounts should ideally be prepared well before the deadline. Late filing penalties are automatic where accounts are delivered late.

Frequently Asked Questions

Why are first company accounts longer than 12 months?

Because the accounting period starts on the incorporation date while the first accounting reference date is normally the last day of the month in which the incorporation anniversary occurs. This commonly creates a first period slightly longer than 12 months.

Can my first company accounts be 18 months long?

They can potentially be extended up to 18 months from the start of the accounting period, subject to the applicable Companies House rules. The normal default arrangement, however, usually produces a first period of just over 12 months.

Are first accounts always more than 12 months?

No. If the first accounting period is 12 months or less, the normal filing rules apply.

Do longer first accounts mean I only file one Corporation Tax return?

Not necessarily. Corporation Tax accounting periods cannot exceed 12 months, so a first set of Companies House accounts covering more than 12 months may require two Corporation Tax returns.

When are my first accounts due?

For a private company whose first accounts cover more than 12 months, they must generally be delivered within 21 months of incorporation or three months from the accounting reference date, whichever is later.

Can I change my company's accounting reference date?

Yes. Companies House permits companies to change their accounting reference date, subject to rules governing the timing and length of accounting periods.

Does changing the year-end affect Corporation Tax?

It can. GOV.UK states that changing a company's financial year will normally affect its Corporation Tax accounting period, and HMRC may need to be updated about the revised dates.

What happens after the first accounting period?

Subsequent accounting periods normally run for 12 months and end on the company's accounting reference date. A private company normally has nine months after the end of that period to file its accounts with Companies House.

Conclusion

The fact that a UK company's first accounts cover more than 12 months is not an error or an unusual exception. It is a normal consequence of how incorporation dates and accounting reference dates work together. For most new private companies, the first accounting period begins on incorporation and ends on the last day of the month in which the incorporation anniversary falls. That naturally creates a first period that is slightly longer than a year.

The crucial point for founders is to distinguish between the accounting period and the filing deadline, and between Companies House reporting and Corporation Tax reporting. Your first statutory accounts can cover more than 12 months, while your Corporation Tax accounting period cannot exceed 12 months. Once the first accounting period is complete, the company's accounts normally settle into a regular 12-month cycle.

For founders, startups and international entrepreneurs establishing a UK company, understanding this distinction early makes the first year far easier to manage and helps prevent the costly assumption that one deadline automatically covers every UK compliance obligation.