Difference between tax year and financial year UK
If you run a business or manage your own finances, you’ve probably heard both terms thrown around. “Tax year” and “financial year” sound like they should mean the same thing, don’t they? But here’s the thing—they don’t. And if you get confused about which is which, it can cost you money and create headaches when you’re filing paperwork with HMRC.
We help business owners and self-employed professionals sort through tax confusion every single day at Tax Care Accountants. This guide breaks down exactly what separates these two terms, why it matters to your wallet, and what you need to do about it.
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Difference Between Tax Year and Financial Year UK
The main difference between the tax year and the financial year in the UK lies in their purpose and the time periods they cover. The UK tax year runs from 6 April to 5 April of the following year and is used by HMRC to calculate and collect personal taxes, including Income Tax, Capital Gains Tax, and PAYE. This period applies to individuals, sole traders, and partnerships and is fixed by law — for example, the 2025/26 tax year covers 6 April 2025 to 5 April 2026.
By contrast, the financial year (also known as the accounting period) refers to the 12‑month period a company chooses for preparing its annual accounts and paying Corporation Tax. Businesses can select their own financial year‑end, though many align it with 31 March, 30 June, or 31 December for convenience. This flexibility allows companies to match their financial reporting with internal or international accounting timelines.
It’s also worth noting that the UK government’s financial year runs from 1 April to 31 March, which it uses for budgeting and public spending rather than individual or corporate taxation.
Why Does April Matter? The Historical Quirk
Here’s something most people don’t know, the April date has a genuinely interesting backstory.
Back in the 1750s, Britain made the switch from the Julian calendar to the Gregorian calendar (bringing ourselves in line with Europe). When the government made this switch in 1752, they had a problem: eleven days literally disappeared from the calendar. The Treasury didn’t want to lose out on tax revenue because of this gap, so they adjusted the financial year start from 25 March to 6 April, exactly 365 days after the previous year started.
That’s why the UK is one of the only places in the world where the tax year doesn’t run on the calendar year. It’s basically a historical accident that stuck around for over 250 years. Pretty mad when you think about it.
Who Needs to Pay Attention to These Dates?
The rules differ depending on what type of business you run, so let’s break this down.
Sole Traders and Partnerships
If you work for yourself or run a partnership, you’ve historically had some choice about your accounting year-end. But here’s where it gets important: the rules changed in April 2024. HMRC now assesses your profits based on the tax year (April 6 to April 5) rather than your accounting year. This means even if your accounts close on December 31st, your tax bill is calculated using the April 6 to April 5 period.
Most accountants now recommend aligning your accounting year-end with either April 5th or March 31st. It sounds like extra work, but it actually saves you time and hassle because everything lines up perfectly. You’re not juggling two different periods, trying to work out which profits fall into which tax year.
Limited Companies
Companies have much more freedom here. When you first set up your company, Companies House assigns an accounting year-end date. But you’re not stuck with it forever. If a different date would suit your business better, you can change it, though you need to notify Companies House and HMRC when you do.
Many companies go with March 31st because it matches the government’s financial year. This means you only deal with one set of corporation tax rates each year. If you choose a different date and your accounting year straddles two different tax years, you could end up working with two different corporation tax rates, which complicates your calculations and your accountant’s work.
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Employees
If you’re employed, the tax year is non-negotiable. Your PAYE tax, National Insurance, and personal tax allowances all run on the April 6 to April 5 schedule. Your personal allowance, ISA allowance, and other tax reliefs all reset on April 6th each year. If you don’t use your allowance, it disappears, you can’t carry it forward to the next year.
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The Dates You Actually Need to Remember
Let’s cut through the background and focus on what matters: when does stuff need to happen?
For the 2025/26 tax year:
- 6 April 2025: Your new tax year begins. Your personal allowances refresh, new tax rates come into effect
- 31 January 2026: Your deadline to file your self-assessment tax return online
- 31 October 2025: Deadline if you’re filing a paper tax return (note this comes first!)
- 31 July 2025: Second payment on account is due if you pay tax in installments
For companies, the timing depends on your specific year-end date. If your accounts close on 30 April, you file your annual accounts by 31 January the following year, and corporation tax is due by 1 February. These timing differences matter because they affect your cash flow and whether you’re paying multiple tax bills in the same month.
Why Your Accounting Year Actually Affects Your Tax Bill
Here’s where the distinction becomes more than just confusing terminology, it can actually affect how much tax you pay.
Imagine this scenario: it’s a corporation tax change year. The government drops corporation tax rates on 1 April. If your accounts run January 1 to December 31, here’s what happens. Your profits from January through March are taxed at the old rate. Your profits from April through December are taxed at the new (lower) rate. You’re calculating tax on two different rates within a single accounting year.
This means more admin work, more calculations, and higher accountancy fees.
Now flip it: your accounts close on 31 March instead. Your profit for April 2025 to March 2026 is calculated against just one corporation tax rate. One calculation, less confusion, less cost. This is why choosing the right year-end matters more than you might think.
For sole traders and partnerships, the same logic applies. By matching your accounting period to the tax year, you sidestep rate changes and simplify everything.
Seasonal Businesses: You Get to Play It Smart
Not every business runs at the same pace throughout the year. If you own a retail shop, your quiet months are probably June and July. Your busiest time is Christmas. Does it make sense to close your accounts mid-holiday rush? Of course not.
Many retailers choose to end their accounting year on 31 January, giving them time after the January sales to settle down and prepare their accounts properly. A tourism business might prefer 30 September if their summer season ends then. A garden centre might choose 31 October after the autumn rush.
The point is, you can use your accounting year to reflect how your business actually works, not some arbitrary date on the calendar. Just remember that whatever year-end you choose, you still report to HMRC using the tax year framework.
The Mistakes We See All the Time
Over the years, we’ve seen the same errors crop up repeatedly. Let’s save you the trouble.
Getting the dates mixed up. People assume April 1st is the tax year start because that’s when the government’s financial year begins. It’s not. April 6th is the correct date for personal tax and self-assessment.
Not planning for rate changes. When tax rates change, they change on 1 April. If your accounting year doesn’t align with this, you end up with split-year calculations and higher accountancy costs. Planning ahead prevents this.
Ignoring the 2024 reforms. If you’re a sole trader or partnership with an accounting year that doesn’t match the tax year, the rules changed significantly in April 2024. Getting ahead of this now means updating your approach today, not scrambling later.
Assuming you can’t change your year-end. You can. Companies can change their date by notifying Companies House. Sole traders have flexibility too. If your current setup isn’t working, change it.
Three Steps to Get Your Ducks in a Row
Step one: Know where you stand. Write down whether you’re a sole trader, partnership, or company. Note your current accounting year-end date. Is it April 5th, 31 March, 31 December, or something else?
Step two: Mark your calendar. January 31st is critical for most people filing self-assessment. If you run a company, write down when your accounts are due and when corporation tax needs paying. These deadlines don’t move, so plan around them.
Step three: Consider alignment. Ask yourself honestly: would aligning my accounting year with the tax year make my life simpler? For most businesses, the answer is yes. The admin is easier, the calculations are cleaner, and your accountancy costs often drop.
The Bottom Line
The difference between tax year and financial year isn’t rocket science once you understand it. The tax year is the government’s baseline for personal taxation (6 April to 5 April). Your accounting year is the period you choose for business reporting (though aligning it with the tax year usually makes sense). For companies, the financial year is the period you pick for your accounts.
Getting these straight stops you from missing deadlines, overpaying tax, and wasting money on accountancy. If you’re unsure whether changes would suit your situation, that’s exactly what we’re here for. At Tax Care Accountants, we help business owners and self-employed professionals untangle tax complexity every day.
If your accounting setup needs a refresh or you’re not sure whether you’re filing correctly, we’d love to have a chat. Give us a call or drop us an email, it often saves thousands down the line.
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