The UK tax system runs on an annual cycle with important deadlines that affect your tax bill, allowances, and financial planning. Missing key dates can cost you money through penalties, lost allowances, or unnecessary tax. This calendar covers everything you need to know.
The Tax Year
The UK tax year runs from 6 April to 5 April. Everything — income tax, capital gains tax, ISA allowances, pension allowances, and most other tax calculations — is assessed over this period.
| Tax Year | Start Date | End Date |
|---|---|---|
| 2024/25 | 6 April 2024 | 5 April 2025 |
| 2025/26 | 6 April 2025 | 5 April 2026 |
| 2026/27 | 6 April 2026 | 5 April 2027 |
Complete Tax Calendar
April
| Date | Event |
|---|---|
| 5 April | End of tax year — last day to use ISA allowance, capital gains annual exempt amount, and pension annual allowance |
| 6 April | New tax year starts — all allowances reset |
Action: Use your ISA, LISA, and Junior ISA allowances before 5 April. These are use-it-or-lose-it.
May–July
| Date | Event |
|---|---|
| 31 May | Employers must issue P60s for the previous tax year |
| 6 July | Employers must submit P11D (benefits in kind) to HMRC |
| 31 July | Second payment on account due for previous tax year’s Self Assessment |
October
| Date | Event |
|---|---|
| 5 October | Deadline to register for Self Assessment if you became self-employed or received untaxed income in the previous tax year |
| 31 October | Paper Self Assessment tax return deadline |
January
| Date | Event |
|---|---|
| 31 January | Online Self Assessment tax return deadline |
| 31 January | Payment of tax owed for the previous tax year |
| 31 January | First payment on account for the current tax year |
Allowances That Reset on 6 April
These allowances start fresh each tax year and cannot be carried forward:
| Allowance | 2025/26 Amount | Use It For |
|---|---|---|
| ISA allowance | £20,000 | Tax-free savings and investing |
| Lifetime ISA | £4,000 (within ISA allowance) | First home or retirement |
| Junior ISA | £9,000 | Tax-free saving for children |
| Personal allowance | £12,570 | Tax-free income |
| Capital gains annual exempt amount | £3,000 | Tax-free capital gains |
| Dividend allowance | £500 | Tax-free dividends |
| Personal savings allowance | £1,000 (basic) / £500 (higher) | Tax-free savings interest |
| Pension annual allowance | £60,000 | Tax-relieved pension contributions |
| Marriage allowance | £1,260 transfer | Tax saving for eligible couples |
End-of-Tax-Year Checklist
Before 5 April each year, review whether you have:
- Used your ISA allowance — contribute up to £20,000 across your ISAs
- Topped up your LISA — up to £4,000 for the 25% government bonus
- Maximised pension contributions — especially if you have unused allowance from previous years (carry forward)
- Used your CGT annual exempt amount — consider “bed and ISA” to use the £3,000 allowance
- Claimed marriage allowance — if eligible, you can backdate up to four years
- Made Gift Aid donations — can be allocated to the previous or current year
- Reviewed your tax code — ensure it is correct by checking your HMRC personal tax account
- Contributed to Junior ISAs — if you have children
Self Assessment Key Dates in Detail
For the 2025/26 tax year (6 April 2025 to 5 April 2026):
| Date | Action |
|---|---|
| 5 October 2026 | Register for Self Assessment (new filers) |
| 31 October 2026 | Paper return deadline |
| 31 January 2027 | Online return + payment deadline |
| 31 July 2027 | Second payment on account |
Late Filing Penalties
| How Late | Penalty |
|---|---|
| 1 day | £100 (automatic) |
| 3 months | £10/day for up to 90 days (max £900) |
| 6 months | 5% of tax owed or £300 (whichever is greater) |
| 12 months | Additional 5% of tax owed or £300 |
Late payment also incurs interest (currently ~7.5% per year) from the day after the deadline.
Planning Around Tax Year Dates
Income Timing
If you have flexibility over when income is received (e.g. self-employment, dividends, bonuses), consider which tax year it falls into:
- If you expect to be a higher rate taxpayer next year but basic rate this year, receive income before 5 April
- If a large lump sum would push you into higher rate, consider deferring to the next tax year
Capital Gains Timing
Spread disposals across tax years to use multiple annual exempt amounts:
- Sell some investments before 5 April, then more after 6 April
- Each tax year gives you a separate £3,000 exemption
Pension Planning
If you have unused pension annual allowance from the past three years, contribute before 5 April to use it before it expires. This can be especially valuable in high-income years.
Check your specific tax situation using our income tax guide and Self Assessment guide.