What happens if I miss the 5 April UK tax year end deadline?

Allowances reset and are lost forever. The £20,000 ISA allowance, the £3,000 Capital Gains Tax annual exempt amount, the £500 Dividend Allowance, and the £1,000 / £500 Personal Savings Allowance do not carry forward to the next tax year. The only exception is the pension annual allowance, where unused allowance from the previous three tax years can be carried forward (subject to having been a pension scheme member). If you forget Marriage Allowance, HMRC will let you backdate a claim up to four tax years, so that one is recoverable.

Do I need an accountant for UK tax year end planning?

For most PAYE employees, no - ISAs, Marriage Allowance, pension top-ups and Gift Aid can all be actioned online without professional help. An accountant becomes useful where you have a limited company, multiple income streams, rental property, capital gains above £50,000, or are approaching the £100,000 Personal Allowance taper or the £60,000 High Income Child Benefit Charge threshold. Self Assessment taxpayers nearing the 31 January deadline with a complex return should engage an accountant by November at the latest.

Can I action everything online through my Personal Tax Account?

Most of it, yes. The HMRC Personal Tax Account (sign in via gov.uk) handles Marriage Allowance applications, Self Assessment filing, payments on account, tax code corrections and Gift Aid declarations through Self Assessment. ISA contributions go through your provider directly. Pension contributions go through your scheme or via SIPP provider. Capital gains realisations happen at your broker. Only the HMRC submissions touch the Personal Tax Account - the rest is provider-side.

Should I rush a pension contribution before 5 April?

Only if you are about to lose unused annual allowance from four years prior. Pension annual allowance carry-forward looks back three tax years, so each 5 April the oldest carry-forward year drops off. If you have substantial unused allowance from 2022/23 that you want to use, the 5 April 2026 deadline is real. Otherwise the £60,000 current-year allowance is still available next year too - rushing a contribution into the last week of March is usually about Income Tax band management (staying below £100,000 or £125,140) rather than the allowance itself.

Does the 5 April deadline matter if I have no investments?

It still matters for Marriage Allowance (£252 saving), Gift Aid carry-back elections, and Self Assessment payments on account. A basic-rate PAYE employee with no savings and no spouse to transfer allowance from genuinely has nothing to do on 5 April - but the moment there is a partner, a charitable donation, or any savings interest above £1,000, the calendar matters.

UK Tax Year End Checklist (2026/27)

The UK tax year ends at midnight on 5 April. Most personal allowances are use-it-or-lose-it: anything unused on 5 April resets to zero on 6 April and is gone forever. The following eight action items cover the allowances and deadlines the typical UK taxpayer should review every January to March window. Every figure below is the 2026/27 statutory amount, verifiable against the gov.uk sources cited in the schema.

None of this is tax advice. Allowances and reliefs vary with personal circumstances - this is a structural checklist of the tax-year-end moves available to UK residents under current HMRC rules.

1. Use your £20,000 ISA allowance

Every UK resident aged 18+ gets a £20,000 Individual Savings Account (ISA) allowance per tax year, split however they choose across Cash, Stocks and Shares, Innovative Finance and Lifetime ISAs (with a £4,000 sub-limit on the Lifetime ISA). All interest, dividends and capital gains inside an ISA are entirely outside UK Income Tax and Capital Gains Tax - and ISA balances do not need to be declared on Self Assessment. Unused allowance does not carry forward: anything not contributed by 5 April is lost.

How to action it: contribute through any ISA provider before 5 April. See the UK ISA allowance explainer for account-type comparison and the £4,000 Lifetime ISA sub-limit detail.

2. Top up your pension toward the £60,000 annual allowance

The standard pension annual allowance is £60,000 for 2026/27, covering combined employer + employee contributions across all your registered pension schemes. Unlike most other allowances, pension annual allowance offers three-year carry-forward: unused allowance from the three previous tax years (2023/24, 2024/25, 2025/26) can be added to the current year's £60,000, provided you were a member of a registered pension scheme in each of those years. Each 5 April the oldest carry-forward year drops off.

For high earners with adjusted income above £260,000 the annual allowance tapers down to a minimum of £10,000. For those who have already flexibly accessed a defined-contribution pension, the Money Purchase Annual Allowance restricts further DC contributions to £10,000 per year.

How to action it: top up via your workplace scheme, SIPP provider, or personal pension. See the pension annual allowance calculator for carry-forward sequencing.

3. Realise gains up to the £3,000 CGT annual exempt amount

The Capital Gains Tax annual exempt amount (AEA) is £3,000 for 2026/27 - down from £12,300 in 2022/23 after two successive cuts. Gains realised inside the £3,000 are entirely free of CGT; gains above it are taxed at 18% (basic rate) or 24% (higher / additional rate) on shares, with residential property at higher rates still. The AEA is a per-person annual amount; it does not carry forward.

A common year-end move is "bed and ISA": selling a holding in a general investment account to crystallise a gain inside the £3,000 allowance, then immediately repurchasing the same holding inside an ISA. This resets the cost basis upward (sheltering future growth from CGT) and uses an otherwise wasted £3,000. The 30-day same-share repurchase rule does not bite because the repurchase is in a different wrapper.

How to action it: place disposals at your broker before 5 April. The UK Capital Gains Tax calculator models the AEA + rate bands.

4. Claim Marriage Allowance for a £252 saving

Marriage Allowance lets one spouse or civil partner transfer £1,260 of their Personal Allowance to the other, provided the transferor earns under £12,570 and the recipient is a basic-rate taxpayer (earning between £12,570 and £50,270 in England / Wales / Northern Ireland; Scottish bands differ slightly). The transfer saves the recipient £252 in Income Tax (£1,260 x 20%) per tax year.

Marriage Allowance is one of the few year-end items that can be backdated: you can claim for the four most recent tax years if eligibility existed, worth potentially £1,000+ in a single successful application. Claims auto-renew once made.

How to action it: apply free at gov.uk via the lower-earning spouse's Personal Tax Account. The Marriage Allowance calculator checks eligibility and shows the cash benefit.

5. Make Gift Aid donations and elect the carry-back

Gift Aid on charitable donations adds 25% to the gross value of the donation (the charity reclaims 20% basic-rate tax on the gross-up). Higher-rate (40%) and additional-rate (45%) taxpayers can claim the difference between their rate and basic rate through Self Assessment - so a £1,000 cash donation costs a higher-rate taxpayer £750 after relief, and an additional-rate taxpayer £687.50.

Gift Aid donations also reduce adjusted net income, which means a strategically-timed donation can claw back lost Personal Allowance in the £100,000-£125,140 60% tax trap, or reduce a High Income Child Benefit Charge between £60,000 and £80,000. The Gift Aid carry-back election (made on the Self Assessment return) lets you treat a donation made between 6 April and the SA filing date as if made in the previous tax year, which is the standard year-end manoeuvre when a 5 April donation deadline was missed but Self Assessment has not been filed yet.

How to action it: tick the Gift Aid box at the charity, then declare donations on Self Assessment with the carry-back election if relevant. The 60% tax trap explainer shows how Gift Aid + pension stack to reduce adjusted net income.

6. Make Self Assessment payments on account and plan for MTD

Self Assessment taxpayers with a previous-year tax liability above £1,000 must usually pay two payments on account each year - one by 31 January and one by 31 July - each equal to half the previous year's tax bill. Any balancing payment is due by the following 31 January with the SA return itself.

If income has fallen materially, you can apply to reduce payments on account - but if the reduction is too aggressive HMRC will charge interest on the underpayment, so the safer route is to overpay and reclaim. For SA-registered taxpayers approaching the deadline, the practical year-end move is to check the 31 January figure now (especially if a payment on account was reduced last summer).

From 6 April 2026, Making Tax Digital for Income Tax Self Assessment (MTD ITSA) applies to self-employed individuals and landlords with gross qualifying income above £50,000 - they must keep digital records and submit quarterly updates via MTD-compatible software. The £30,000-£50,000 band joins from April 2027.

How to action it: log into the Personal Tax Account at gov.uk to check next payment-on-account amount and Self Assessment status. See the MTD ITSA 2026 explainer for who is in scope and what software qualifies.

7. Use the Personal Savings Allowance for tax-free interest

The Personal Savings Allowance shelters the first £1,000 of savings interest from tax for basic-rate taxpayers, £500 for higher-rate taxpayers, and £0 for additional-rate taxpayers. Interest above the allowance is taxed at the saver's marginal Income Tax rate. There is also a £5,000 Starting Rate for Savings band available to those with non-savings income below £17,570 - tapered against the Personal Allowance.

The Personal Savings Allowance does not carry forward and is not strictly a "deadline" item, but the year-end review is where most taxpayers check whether interest income has exceeded the allowance (triggering Self Assessment registration if not already registered) or whether they should shift cash into a Cash ISA where interest is entirely outside the cap.

How to action it: review your savings interest statements for the year; if approaching the cap, move balances to a Cash ISA before 5 April. See the Personal Savings Allowance explainer for rate-band interaction.

8. Use the £500 Dividend Allowance

The Dividend Allowance is £500 for 2026/27, down from £2,000 in 2022/23 after two successive cuts. Dividends received inside the £500 are tax-free; above it, dividends are taxed at 8.75% (basic), 33.75% (higher) or 39.35% (additional) depending on the recipient's other income. The Dividend Allowance does not carry forward.

For limited-company directors taking a tax-efficient mix of salary plus dividends, the £500 allowance is usually consumed automatically by the first dividend of the year - the year-end check is more about timing the final declaration to land in the current tax year vs the next, where marginal rate or Personal Allowance taper considerations differ.

How to action it: dividends paid by a personal limited company must be declared and paid in cash by 5 April to count for the current tax year. See the Dividend Allowance explainer and the Dividend Tax calculator for rate-band sequencing.

Key UK tax year dates to know

5 April - last day of the UK tax year. Use-it-or-lose-it allowances reset at midnight.
6 April - first day of the new tax year. New allowances available; from 6 April 2026, MTD ITSA begins for £50k+ self-employed / landlords.
31 July - second Self Assessment payment on account due.
5 October - deadline to register for Self Assessment if you have new untaxed income from the previous tax year.
31 October - paper Self Assessment return deadline.
30 December - online SA filing deadline if you want HMRC to collect tax owed via PAYE coding adjustment (for liabilities under £3,000).
31 January - online Self Assessment filing + balancing payment + first payment on account, all due the same day.

Frequently asked questions

What happens if I miss the 5 April UK tax year end deadline?: Allowances reset and are lost forever. The £20,000 ISA allowance, the £3,000 Capital Gains Tax annual exempt amount, the £500 Dividend Allowance, and the £1,000 / £500 Personal Savings Allowance do not carry forward to the next tax year. The only exception is the pension annual allowance, where unused allowance from the previous three tax years can be carried forward (subject to having been a pension scheme member). If you forget Marriage Allowance, HMRC will let you backdate a claim up to four tax years, so that one is recoverable.
Do I need an accountant for UK tax year end planning?: For most PAYE employees, no - ISAs, Marriage Allowance, pension top-ups and Gift Aid can all be actioned online without professional help. An accountant becomes useful where you have a limited company, multiple income streams, rental property, capital gains above £50,000, or are approaching the £100,000 Personal Allowance taper or the £60,000 High Income Child Benefit Charge threshold. Self Assessment taxpayers nearing the 31 January deadline with a complex return should engage an accountant by November at the latest.
Can I action everything online through my Personal Tax Account?: Most of it, yes. The HMRC Personal Tax Account (sign in via gov.uk) handles Marriage Allowance applications, Self Assessment filing, payments on account, tax code corrections and Gift Aid declarations through Self Assessment. ISA contributions go through your provider directly. Pension contributions go through your scheme or via SIPP provider. Capital gains realisations happen at your broker. Only the HMRC submissions touch the Personal Tax Account - the rest is provider-side.
What changes for tax year end from April 2026 with MTD ITSA?: Making Tax Digital for Income Tax Self Assessment (MTD ITSA) phases in from 6 April 2026 for self-employed individuals and landlords with gross income above £50,000, and from April 2027 for the £30,000-£50,000 band. Affected taxpayers must keep digital records and submit quarterly updates via MTD-compatible software instead of a single annual Self Assessment return. The 31 January annual deadline remains, but quarterly updates start landing each summer / autumn / winter. PAYE-only taxpayers are unaffected.
Should I rush a pension contribution before 5 April?: Only if you are about to lose unused annual allowance from four years prior. Pension annual allowance carry-forward looks back three tax years, so each 5 April the oldest carry-forward year drops off. If you have substantial unused allowance from 2022/23 that you want to use, the 5 April 2026 deadline is real. Otherwise the £60,000 current-year allowance is still available next year too - rushing a contribution into the last week of March is usually about Income Tax band management (staying below £100,000 or £125,140) rather than the allowance itself.
Does the 5 April deadline matter if I have no investments?: It still matters for Marriage Allowance (£252 saving), Gift Aid carry-back elections, and Self Assessment payments on account. A basic-rate PAYE employee with no savings and no spouse to transfer allowance from genuinely has nothing to do on 5 April - but the moment there is a partner, a charitable donation, or any savings interest above £1,000, the calendar matters.