The 23/24 UK tax year dates run from 6 April 2023 to 5 April 2024. Any employment income, dividends, savings interest, rental income, or capital gains you received in that twelve-month window falls into this reporting cycle, with filing and payment deadlines stretching into 2025 and a set of annual allowances that had to be used before midnight on 5 April 2024.
The Exact Start and End Dates
The tax year began on 6 April 2023 and ended on 5 April 2024. Section 4 of the Income Tax Act 2007 defines a tax year as the period starting on 6 April and ending on the following 5 April, with each year identified by the calendar year in which it begins.1Legislation.gov.uk. Income Tax Act 2007 – Section 4
The April start date is a legacy of Britain’s 1752 switch from the Julian to the Gregorian calendar. The Treasury shifted the tax year forward to avoid losing eleven days of revenue, and the date has never moved since. Every deadline that follows is anchored to that 5 April year-end.
Filing Deadlines for the 23/24 Return
If you needed to submit a Self Assessment return covering the 23/24 year, paper returns were due by midnight on 31 October 2024. Online returns had until midnight on 31 January 2025.2GOV.UK. Self Assessment Tax Returns: Deadlines
If you were not already registered for Self Assessment, you had to notify HMRC within six months of the end of the tax year. Section 7 of the Taxes Management Act 1970 sets that notification period at six months from 5 April 2024, giving a deadline of 5 October 2024.3Legislation.gov.uk. Taxes Management Act 1970 – Section 7 Missing this registration window triggers its own penalties, separate from any late-filing charge.
Payment Deadlines
The balancing payment for any 23/24 tax still owed was due by midnight on 31 January 2025. That same date was also the deadline for the first payment on account toward 24/25, provided your 23/24 tax bill exceeded £1,000.4GOV.UK. Understand Your Self Assessment Tax Bill: Payments on Account
The second payment on account falls due by 31 July 2025. Each payment on account is half of your previous year’s tax bill and is meant to spread the current year’s liability across two instalments.
You do not need to make payments on account if your 23/24 tax bill was under £1,000, or if more than 80% of your tax was already collected at source through PAYE. If your income has since dropped, you can apply to reduce the payments on account, but if you underestimate, HMRC will charge interest on the shortfall.
Rates and Allowances That Applied in 23/24
The personal allowance for 23/24 was £12,570. Above that, taxable income fell into three bands:5UK Parliament. Direct Taxes: Rates and Allowances 2023/24
- Basic rate of 20% on taxable income up to £37,700, covering total income up to £50,270 once the personal allowance is added.
- Higher rate of 40% on taxable income from £37,701 to £125,140.
- Additional rate of 45% on taxable income above £125,140.
The personal allowance tapers away for income above £100,000, reducing by £1 for every £2 earned over that threshold, and disappears entirely once total income reaches £125,140.
The dividend allowance for 23/24 was £1,000, so the first £1,000 of dividend income was tax-free regardless of tax band.6GOV.UK. Check if You Have to Pay Tax on Dividends The personal savings allowance gave basic-rate taxpayers £1,000 and higher-rate taxpayers £500 of tax-free savings interest. Additional-rate taxpayers received no savings allowance.7GOV.UK. Tax on Savings Interest: How Much Tax You Pay
Allowances That Expired on 5 April 2024
Several allowances tied to 23/24 could not be carried into the following year. If they were not used by midnight on 5 April 2024, they were gone.
ISA Allowance
The ISA contribution limit for 23/24 was £20,000 across all ISA types combined, including Cash, Stocks and Shares, Lifetime, and Innovative Finance ISAs.8UK Parliament. Cash Individual Savings Account Unused allowance cannot be rolled forward.
Capital Gains Tax Annual Exempt Amount
The CGT annual exempt amount for 23/24 was £6,000 for individuals, down from £12,300 in 2022/23.9GOV.UK. Capital Gains Tax Rates and Allowances Gains up to £6,000 within the year were tax-free; any unused portion vanished at year-end.
Pension Annual Allowance
The pension annual allowance for 23/24 was £60,000, up from £40,000 the previous year. Unlike ISAs and CGT, unused pension allowance can be carried forward from the three previous tax years if you were a member of a registered pension scheme during those years. Carry forward works on a first-in, first-out basis: the current year’s allowance must be used first, then the earliest available year. That made 23/24 the last chance to use any unused allowance from 2020/21.
Dividend Allowance
The £1,000 dividend allowance for 23/24 was also use-it-or-lose-it.6GOV.UK. Check if You Have to Pay Tax on Dividends It had already dropped from £2,000 in 2022/23, and fell again to £500 from 2024/25.
What It Costs to Miss the 23/24 Deadlines
Late filing triggers an automatic £100 penalty the moment you miss the deadline, even if you owe no tax. After three months, HMRC adds £10 per day for up to 90 days, capped at £900. At six months late, there is a further penalty of 5% of the tax due or £300, whichever is higher. At twelve months, another 5% or £300 applies, and in cases involving deliberate withholding this can reach 100% of the tax owed.10GOV.UK. Self Assessment Tax Returns: Penalties
Late payment carries its own surcharges: 5% of the outstanding tax at 30 days, another 5% at six months, and a further 5% at twelve months. Interest also runs from the day after the payment deadline. For the 31 January 2025 deadline the late payment interest rate was the Bank of England base rate plus 2.5%. From 6 April 2025 that rate increased to the base rate plus 4%, so any 23/24 tax still outstanding after that date accrues interest faster.11GOV.UK. HMRC Interest Rates for Late and Early Payments