For many UK business owners, the end of the financial year is a period of high stress, involving a flurry of receipts, invoices, and discussions with accountants. However, the date your financial year ends—known as your Accounting Reference Date (ARD)—isn’t set in stone. Whether you want to align your business year with the tax year (April 5th), the calendar year (December 31st), or simply a quieter period in your industry, shortening your accounting period is a powerful administrative tool.
But while changing your year-end date might seem like a simple box-ticking exercise on Companies House, it has a significant “domino effect” on your Corporation Tax obligations. If you are considering this move for your company, it is vital to understand how it accelerates your deadlines and changes your reporting relationship with HMRC.
What Happens When You Shorten Your Accounting Period (Quick Answer)
In short: Shortening your accounting period brings all your filing and payment deadlines forward. If you shorten your financial year, the Companies House and HMRC “clock” begins running from that new earlier financial year end, and critically, you are responsible for making sure HMRC’s own records are updated to match, since this doesn’t always happen automatically.
For instance, if your year end is 31st December and you cut it back to 30th September, then not only have you altered the numbers on your balance sheet, you have also unknowingly brought your tax payment date and your filing date a few months forward. This can leave you in a sudden cash flow crisis if you haven’t planned for the tax bill in the past.
Companies House Deadline vs Corporation Tax Deadline: What’s the Difference?
To navigate a shortening accounting period successfully, you must first distinguish between the two separate regulatory bodies you report to: Companies House and HMRC.
- Companies House: This is the UK’s registrar of companies. They are concerned with your “statutory accounts,” which are made public. For a private limited company, the deadline to file accounts is usually nine months after the end of the accounting period, but if you’ve just shortened your period, this rule changes. The new filing deadline becomes whichever is later: 3 months from the date Companies House receives your AA01, or 9 months from your new year-end.
- HMRC: The tax authorities are concerned with your Corporation Tax. They require two things:
- Payment: Usually due nine months and one day after the end of your accounting period.
- The Tax Return (CT600): Usually due 12 months after the end of the accounting period.
When you shorten your period, both sets of deadlines are recalculated based on the new end date. Companies House and HMRC are separate systems, and updating one does not automatically update the other — more on this below.
How Shortening Your Accounting Period Changes Your Corporation Tax Dates
When you decide on shortening your accounting period, your Corporation Tax deadlines move in tandem with your new Accounting Reference Date.
In normal years, the due date to pay tax is Jan. 1st, 2027, if your year ends on March 31st, 2026. When you shorten that period to December 31st, 2025, all of a sudden this payment date becomes October 1st, 2026.
The most important thing to remember is that Corporation Tax is charged on profits for an “accounting period for tax.” Usually, this matches your company’s financial year. If you shorten your financial year to six months, you will have a six-month tax period. You will still need to file a CT600 for that shortened period, and the deadline will be 12 months from the new end date. However, because the period is shorter, the profit generated in that time is what will be taxed, which may result in a smaller-than-usual tax bill—though it will be due much sooner.
One thing that often catches business owners out: your tax-free thresholds shrink along with your accounting period. The £50,000 small profits threshold (below which the 19% rate applies) and the £250,000 upper threshold are both scaled down proportionately for a period shorter than 12 months — and divided further if your company has associated companies. A six-month accounting period, for example, halves both thresholds. This can push a company into marginal relief, or even the main rate, sooner than the raw profit figure might suggest.
Do You Need to Notify HMRC When You Shorten Your Accounting Period?
The short answer is: Yes, and you shouldn’t assume it happens automatically. GOV.UK is explicit on this point: if you’ve shortened or lengthened your financial year, you must update your accounting period dates with HMRC yourself. Companies House and HMRC are separate registers, and while there is often some data-sharing in practice, it isn’t a guaranteed or instant handoff you can rely on.
In practice, this means:
- If your new dates and HMRC’s records don’t match, contact HMRC directly rather than assuming Companies House will sort it out — this is especially important if you’re close to a filing deadline, since a mismatch can trigger an automated late-filing notice even when you filed on time against your actual new dates.
- Log in to your Corporation Tax business tax account and check the accounting period dates HMRC holds — do this a few weeks after filing your AA01.
- If you use accounting software to file your CT600, update the new period dates in the software before you file, so HMRC’s system doesn’t reject or misdate the return.
Shortening vs Lengthening Your Accounting Period: Which One Do You Need?
Businesses often confuse these two actions, but they have very different rules and consequences:
- Shortening Your Accounting Period: This involves moving your year-end to an earlier date. You can do this as many times as you like, and you can shorten a period by as little as one day. It is often used to align with a parent company or a specific tax year.
- Lengthening Your Accounting Period: This involves pushing your year-end to a later date (up to a maximum of 18 months). Unlike shortening, you can generally only lengthen your period once every five years, unless the company is in administration or you are aligning with a subsidiary/parent company.
If you are struggling to meet a deadline, lengthening might seem attractive, as it gives you more time, but because of the “once every five years” rule, many businesses choose to shorten their next period instead to achieve their desired alignment.
Regulatory watch (2026): Under the Economic Crime and Corporate Transparency Act, the government proposed restricting shortening to once every five years too, the same limit currently applied to lengthening, unless a company can show a “valid business reason.” This change was originally pencilled in for April 2027 but has since been paused pending a final government decision. Nothing has changed yet, so the “shorten as often as you like” rule still applies today, but it’s worth knowing this is under review if you’re planning to rely on repeated shortening as a long-term strategy.
Can You Shorten Your Accounting Period If You’re Close to Missing a Deadline?
This is a common “emergency” tactic used by companies facing late filing penalties. Yes, you can shorten your accounting period even if you are close to a deadline, provided the deadline for filing those accounts has not already passed.
If you realise you cannot get your accounts ready for a December 31st year-end by the September deadline, you could (in theory) shorten the period to November 30th. This would technically reset your filing clock. However, this is a complex move that should only be done under professional guidance, as it can look like “deadline dodging” to regulators and may trigger closer scrutiny of your accounts. Furthermore, it only delays the inevitable—you still have to file accounts eventually.
Worth knowing: once your accounts are actually overdue, this option disappears. Companies House will not let you change your year end for a period once its filing deadline has passed; you’ll need to file the overdue accounts (and any penalty) first, then consider changing your reference date going forward.
Shortening Your First Accounting Period: What’s Different?
New companies often find their first accounting period is slightly longer than 12 months. This happens because Companies House automatically sets your first year-end as the last day of the month in which you incorporated, one year later.
For example, if you incorporate on May 15th, 2025, your first year-end will be May 31st, 2026. This is a period of 12 months and 16 days. Many business owners prefer a clean 12-month period and choose to shorten the accounting period to end on May 14th or May 31st of the same year.
Warning: HMRC does not allow a single tax return to cover more than 12 months. If your first period is 12 months and two weeks, you will actually have to file two Corporation Tax returns: one for the first 12 months and one for the final two weeks. Shortening your first period to exactly 12 months or less simplifies this into a single return.
How to Find Your Exact New Corporation Tax Deadline
Once you have processed the change through Companies House, you can find your new deadlines by:
- Checking Companies House Service: Search for your company name on the public register. The “Accounts” tab will show your new “Next accounts made up to” date and the “Due by” date.
- HMRC Online Account: Log in to your Corporation Tax for Organisations portal. It will list your accounting periods and the date payment is due.
- The “9 Month Rule”: This applies to your Corporation Tax payment date only; simply take your new year-end date and add nine months and one day. That is your payment deadline. Add 12 months for your filing deadline. Remember, your Companies House accounts deadline follows the separate “whichever is later” rule covered above; don’t apply this 9-month shortcut to that one.
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FAQs: Frequently Asked Questions
How many times can I shorten my company’s accounting period?
You may shorten your accounting period as many times as you want. While you can only lengthen once every five years, you can shorten your period at will each year if you want to, although it may be difficult to make year-on-year comparisons if you do this too often and confuse your investors. (See the regulatory watch note above; this may change to a five-year limit in future.)
What is the minimum period I can shorten my accounting period by?
The lowest is 1 day. When it comes to the time of a period, this is a very small cut in time and is legally acceptable. Most businesses will reduce their length of time by months so that it can fit into a specific date, such as the end of a quarter.
Will shortening my accounting period affect my VAT or payroll deadlines?
Generally, no. VAT periods and PAYE (payroll) deadlines operate on their own independent cycles. VAT is typically based on a quarterly cycle, and PAYE is monthly. If you are on the VAT Annual Accounting Scheme, then your VAT return will be aligned with your financial year, so reducing the period will impact the date for filing your VAT return.
Does shortening my accounting period reduce the total tax I pay?
No. Shortening changes the timing of when profits are reported and taxed, not the total amount due over the life of the business. It can help with cash flow and loss relief timing, but it isn’t a way to reduce your overall Corporation Tax liability.
Can I shorten my accounting period if my accounts are already overdue?
No. You cannot change your accounting reference date for a period if the filing deadline for that period has already passed. Once you are late, you are late. You must file the accounts as they stand and pay the associated penalties before you can change future dates.
Does shortening my accounting period cost anything?
Filing the change (Form AA01) with Companies House is free if done online. However, you may incur costs from your accountant, as they will need to prepare accounts for a non-standard period and potentially adjust your tax computations.
How long does it take Companies House to process a shortened accounting period?
It is usual to have the change in the public register almost instantaneously, and the change is often lodged electronically and completed within 24 hours. Paper filing may be several weeks.
Do I need an accountant to shorten my accounting period?
While you can technically do it yourself via the Companies House website, it is highly recommended to use an accountant such as MyIVA. Because the change affects your Corporation Tax periods and can result in needing to file multiple returns (if you accidentally lengthen or have a complex start-up period), MyIVA’s professional advice ensures you don’t inadvertently trigger penalties or miss an accelerated tax payment date.
Conclusion
Shortening your accounting period is more than just a calendar change; it is a strategic move that can help align your business with its natural cycle or simplify your administrative burden. However, the primary consequence is the acceleration of your Corporation Tax deadline, not a change in the total tax you owe.
By moving your year-end forward, you are essentially telling HMRC that you will settle your debts sooner. For companies with healthy cash flow, this is rarely an issue. But for businesses in a tighter spot, that three- or four-month jump in the tax deadline can be a shock. Always consult with a professional like MyIVA to ensure that while you are shortening your year, you aren’t also shortening your company’s financial lifeline.
