What Is the UK Tax Year: 6 April Start, Bands, and Deadlines

The UK tax year runs from 6 April to 5 April the following year. The current one began on 6 April 2025 and ends on 5 April 2026, and it’s written in shorthand as “2025/26.” Every pound of income you earn, every capital gain you realise, and every tax-free allowance you use is measured against that 12-month window. Once 5 April passes, unused allowances are gone and a fresh cycle starts.¹

The timing matters more than it looks. A bonus paid on 4 April counts in one tax year; the same bonus paid on 7 April counts in the next. That difference can push you into a higher band or let you use an allowance you would otherwise lose.

Allowances That Reset on 6 April

Several tax-free thresholds restart at the beginning of each tax year, and you can’t carry the unused portion forward. If you haven’t used them by 5 April, they expire.

Personal Allowance of £12,570 before any income tax is due. It tapers by £1 for every £2 of income above £100,000 and disappears at £125,140.²
ISA allowance of £20,000 across all your Individual Savings Accounts, with any interest or growth inside tax-free. The limit is frozen until at least 2030.³
Capital gains tax allowance of £3,000 on profits from selling assets like shares or a second property.⁴
Pension annual allowance of £60,000 for contributions receiving tax relief, though this reduces for very high earners.⁵

Income Tax Bands for 2025/26

Within the tax year, income above the Personal Allowance is taxed in bands. The basic rate of 20% applies to taxable income between £12,571 and £50,270. The higher rate of 40% covers £50,271 to £125,140. The additional rate of 45% applies above £125,140.² These thresholds have been frozen for several years, so inflation has quietly pulled more earners into higher bands.

Do You Need to File a Self Assessment Return?

Most employees never file a return because tax is deducted at source through PAYE. Self Assessment exists for income HMRC can’t collect that way. You need to file if, during the tax year, any of these applied:

You worked as a sole trader and earned more than £1,000 before deductions.
You were a partner in a business.
You sold an asset and owed capital gains tax.
You or your partner earned over £60,000 and received Child Benefit (the High Income Child Benefit Charge).
You had significant income from property, savings, dividends, tips, or foreign sources.⁶

Filing for the first time means registering with HMRC by 5 October after the tax year ends. For 2025/26, that’s 5 October 2026.⁷

Deadlines After the Tax Year Ends

Once 5 April passes, a run of deadlines follows. For the 2025/26 year:

5 April 2026: tax year ends. Last day to use ISA, pension, and capital gains allowances.
5 October 2026: register for Self Assessment if you’ve never filed.
31 October 2026: paper tax returns due.
31 January 2027: online returns due, and any remaining tax for 2025/26 payable.¹

Payments on Account

If your Self Assessment bill tops £1,000 and less than 80% of your tax was collected at source, HMRC asks for two advance payments toward next year’s liability. Each is half of the previous year’s total. The first falls on 31 January alongside the balancing payment for the prior year; the second is due on 31 July.¹ So 31 January is often a triple hit.

Penalties if You Miss Them

HMRC’s penalties escalate, and filing charges and payment charges stack separately.

Miss the 31 January online deadline by even a day and you get an automatic £100 fine, whether or not you owe any tax. After three months, daily penalties of £10 apply for up to 90 days, adding up to £900. Further penalties follow at six and twelve months, calculated as a percentage of the tax due or a fixed minimum, whichever is greater.⁸

Unpaid tax attracts its own surcharges: 5% of the outstanding amount at 30 days, another 5% at six months, and another 5% at twelve months.⁸ Interest runs on top. As of January 2026, the late payment interest rate is 7.75%, set at the Bank of England base rate plus 4%.⁹ A £5,000 bill left unpaid for a full year attracts more than £750 in surcharges before interest is added.

HMRC will consider an appeal if you had a “reasonable excuse.” Accepted reasons include serious illness or hospitalisation, bereavement of a close relative, fire or flood destroying your records, and failures of HMRC’s own online systems.¹⁰ You’ll need documentary evidence, and you must file or pay as soon as the obstacle clears. Forgetting or not knowing doesn’t count.

Why 6 April?

The odd start date comes from a calendar change in 1752, when Britain moved from the Julian to the Gregorian calendar and dropped 11 days from September. The Treasury didn’t want to lose 11 days of tax revenue, so it extended the tax year and shifted its start from 25 March (Lady Day) to 5 April. A further one-day adjustment in 1800 pushed it to 6 April, where it has stayed.

Not the Same as the Government Fiscal Year

The 6 April to 5 April cycle applies to individuals. The government’s own fiscal year for national budgeting runs from 1 April to 31 March. That five-day gap means a change announced as effective “at the start of the new financial year” on 1 April doesn’t affect your personal tax position until 6 April.

Limited companies follow a different calendar again. A company’s accounting period for Corporation Tax is set when it registers and can’t exceed 12 months, but the dates are flexible.¹¹ Many pick 31 March or 31 December, but there’s no requirement to align with either the personal tax year or the government’s fiscal year. Trusts and estates, by contrast, do share the 6 April to 5 April cycle used by individuals.¹²

If You’re a US Citizen in the UK

US citizens and green card holders file in both countries, and the mismatched tax years create real complications. The US tax year follows the calendar (1 January to 31 December), so one UK tax year straddles two US returns: UK income from 6 April to 31 December goes on one, and 1 January to 5 April goes on the next.

When claiming foreign tax credits on IRS Form 1116 for UK tax paid, you can choose the paid or accrued basis. Accrued taxes generally convert using the average exchange rate for the year they relate to. If accrued foreign taxes aren’t actually paid within 24 months after the close of the tax year, you must reduce the credit previously claimed and won’t get credit for those taxes until you pay them.¹³ If both countries could treat you as resident, the US-UK tax treaty applies tie-breaker rules so only one does.¹⁴

1
GOV.UK. Self Assessment Tax Returns: Deadlines
2
GOV.UK. Income Tax Rates and Personal Allowances
3
GOV.UK. Individual Savings Accounts (ISAs): Withdrawing Your Money
4
GOV.UK. Capital Gains Tax Rates and Allowances
5
GOV.UK. Pension Schemes Rates
6
GOV.UK. Self Assessment Tax Returns: Who Must Send a Tax Return
7
GOV.UK. Self Assessment Tax Returns: Registering
8
GOV.UK. Self Assessment Tax Returns: Penalties
9
GOV.UK. HMRC Interest Rates for Late and Early Payments
10
GOV.UK. Reasonable Excuse: Examples of Reasonable Excuse
11
GOV.UK. Accounting Periods for Corporation Tax
12
GOV.UK. Trust and Estate Tax Return Guide 2025
13
Internal Revenue Service. Instructions for Form 1116 (2025)
14
Internal Revenue Service. Technical Explanation of the Convention Between the Government of the United States of America and the Government of the United Kingdom for the Avoidance of Double Taxation