What Is the UK Tax Year: Dates, Allowances, and Deadlines

The UK tax year runs from 6 April to 5 April the following year. The current one started on 6 April 2025 and ends on 5 April 2026, and it’s written as “2025/26” on official documents. Every pound you earn, every gain you realise, and every tax-free allowance you’re entitled to falls inside that 12-month window. Once 5 April passes, unused allowances are gone.

When the Year Starts and Ends

HM Revenue and Customs (HMRC) measures your tax position over a fixed period beginning on 6 April and ending on 5 April.1GOV.UK. Self Assessment Tax Returns: Deadlines Those dates set the boundaries for your income tax bands, your annual savings and pension limits, and the reference point for every deadline that follows.

The date a payment lands matters. A bonus paid on 4 April counts in one tax year; the same bonus paid on 7 April counts in the next. That timing can push you into a higher band or let you use an allowance that would otherwise expire.

Allowances That Reset on 6 April

Several tax-free thresholds restart at the top of each tax year. If you don’t use them by 5 April, they don’t roll over.

Income Tax Bands for 2025/26

The Personal Allowance and income tax bands have been held at their current levels for several years. For 2025/26, 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, and the additional rate of 45% applies above £125,140.2GOV.UK. Income Tax Rates and Personal Allowances

Who Has to File a Self Assessment Return

Most employees never file a return because income tax is deducted at source through PAYE. Self Assessment is required when HMRC can’t collect what you owe automatically. 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 partnership.
  • 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.
6GOV.UK. Self Assessment Tax Returns: Who Must Send a Tax Return

If you need to file for the first time, register with HMRC by 5 October following the end of the tax year.7GOV.UK. Self Assessment Tax Returns: Registering For 2025/26, that registration deadline is 5 October 2026.

Key Deadlines After the Year Ends

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

Payments on Account

If your Self Assessment bill is over £1,000 and less than 80% of your tax was collected at source, HMRC asks for two advance payments toward the following year’s bill. Each equals half of the previous year’s total liability. The first is due on 31 January alongside the balancing payment for the prior year, and the second on 31 July.1GOV.UK. Self Assessment Tax Returns: Deadlines That makes 31 January a triple hit in many cases: the balancing payment for the old year plus the first advance for the new one.

How Long to Keep Records

Keep your financial records for at least five years after the 31 January submission deadline of the relevant tax year.8GOV.UK. Business Records if You’re Self-Employed: How Long to Keep Your Records For 2025/26, that means holding onto them until at least 31 January 2032. Filing late stretches the retention period further.

Penalties for Late Filing and Late Payment

HMRC runs two separate penalty regimes, and the charges stack.

Late Filing

Miss the 31 January online deadline by a single day and you get an automatic £100 fine, whether or not you owe tax. If the return is still outstanding after three months, daily penalties of £10 kick in for up to 90 days, adding a maximum of £900. Further penalties apply at six and twelve months, calculated as a percentage of the tax due or a minimum fixed amount, whichever is greater.9GOV.UK. Self Assessment Tax Returns: Penalties

Late Payment

Unpaid tax attracts a 5% surcharge at 30 days, another 5% at six months, and another 5% at twelve months.9GOV.UK. Self Assessment Tax Returns: Penalties 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%.10GOV.UK. HMRC Interest Rates for Late and Early Payments A £5,000 bill left unpaid for a full year could attract over £750 in surcharges before interest is added.

Appealing a Penalty

HMRC accepts appeals where you had a “reasonable excuse.” Examples that are typically accepted include serious illness or hospitalisation, bereavement of a close relative, fire or flood destroying your records, and technical failures with HMRC’s online systems.11GOV.UK. Reasonable Excuse: Examples of Reasonable Excuse You’ll need documentary evidence, and you must file or pay as soon as the obstacle is removed. Forgetting, or not knowing you had to file, is almost never accepted.

Other UK Financial Periods That Aren’t the Tax Year

The 6 April to 5 April cycle covers individuals. Other entities work to different calendars, and mixing them up is easy.

The government’s own fiscal year for national budgeting runs from 1 April to 31 March. A policy change taking effect “at the start of the new financial year” on 1 April won’t hit your personal tax position until 6 April.

Limited companies don’t follow the personal tax year. A company’s Corporation Tax accounting period is set when it registers and can’t exceed 12 months, but the specific dates are flexible.12GOV.UK. Accounting Periods for Corporation Tax Many companies 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 do follow the same 6 April to 5 April cycle as individuals.13GOV.UK. Trust and Estate Tax Return Guide 2025 Where a trust holds a trading business, the accounting period for that trade income may differ from the tax year, creating timing adjustments in the return.

If You’re a US Citizen With UK Income

US citizens and green card holders in the UK file in both countries, and the mismatched years complicate things. The US tax year is the calendar year (1 January to 31 December), so a single UK tax year straddles two US returns: UK income from 6 April to 31 December falls in one, and 1 January to 5 April falls in the next.

When claiming foreign tax credits on IRS Form 1116 for UK taxes paid, you can report them on a paid or accrued basis. If you accrue, you generally use the average exchange rate for the tax year they relate to. Accrued foreign taxes not actually paid within 24 months after the close of the relevant tax year require you to reduce the credit previously claimed, and credit isn’t available again until you pay them.14Internal Revenue Service. Instructions for Form 1116 (2025)

If both countries could treat you as resident, the US-UK tax treaty applies tie-breaker rules in order: where you have a permanent home, where your closest personal and economic ties are, where you habitually live, and finally your nationality.15Internal 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 The treaty settles you as resident of one country, which decides which side gets first taxing rights on your income.