Self Assessment: who needs to file, the deadlines, and the payments on account surprise

HMRC requires you to file a Self Assessment return if any of the following apply to you. This list covers the most common reasons — verify the complete and up-to-date list at GOV.UK Self Assessment eligibility:

• You are self-employed and your trading income was more than £1,000 in the tax year
• You are a company director (of a company that has not been dormant throughout the year)
• Your total taxable income was over £100,000
• You have income from renting out property
• You received untaxed income of more than £2,500 (verify the current threshold at GOV.UK)
• You have savings income or investment income on which tax is owed
• You receive dividends from shares and owe tax on them
• You need to claim specific reliefs (such as Gift Aid higher-rate relief that was not claimed through PAYE)
• You or your partner received Child Benefit and your income was over the High Income Child Benefit Charge threshold (verify at GOV.UK — this threshold changed in the April 2024 Budget)
• HMRC sends you a notice requiring you to file, regardless of your circumstances

If you are employed and all your tax is collected through PAYE, and none of the above applies, you generally do not need to file.

You register through your Government Gateway account on GOV.UK. If you do not have a Government Gateway account, you will need to create one first.

For self-employed people, the registration process also tells HMRC you are trading. You will need to register as self-employed by 5 October following the end of the tax year in which you started. So if you started trading in the 2024/25 tax year (which ended 5 April 2025), you must register by 5 October 2025.

Missing the registration deadline can result in a penalty. Registering early also gives you more time to gather your records and understand what you owe before the filing deadline.

Once registered, HMRC will issue you a UTR (Unique Taxpayer Reference) within around 10 working days. Keep it safe — you need it for every Self Assessment interaction.

Register for Self Assessment on GOV.UK.

These deadlines apply to the standard Self Assessment cycle. Always verify at GOV.UK because deadlines can change, and some circumstances have different rules:

• 5 October — deadline to register for Self Assessment if you are newly self-employed or newly need to file
• 31 October — deadline to file a paper return for the previous tax year
• 31 January — deadline to file your online return for the previous tax year, and to pay any tax owed (the balancing payment)
• 31 January — first payment on account for the current tax year also due on the same date
• 31 July — second payment on account for the current tax year

The tax year runs from 6 April to 5 April the following year. So your return for the 2024/25 tax year (6 April 2024 to 5 April 2025) must be filed by 31 January 2026.

Check current deadlines on GOV.UK.

Payments on account are the biggest shock for first-time Self Assessment filers, and HMRC does not make them easy to understand. Here is what they are and why they matter.

When you file your first Self Assessment return, HMRC calculates not only the tax you owe for the year just ended, but also assumes you will earn a similar amount in the following year. To avoid a large bill in one go the next January, they collect two advance payments toward next year's tax bill.

Each payment on account is 50% of your previous year's tax bill. They are due in January and July.

Worked example: Suppose your first Self Assessment return shows you owe £2,000 in tax for the year. When January comes, HMRC sends you a bill for:

• £2,000 for the year just ended (the balancing payment)
• £1,000 as the first payment on account toward the following year (50% of £2,000)

Your January payment is £3,000, not £2,000.

Then in July, you pay a second payment on account of £1,000. So in total across your first full Self Assessment cycle, you pay £4,000, not £2,000.

When you file the following year, your payments on account are offset against the total owed. If you actually owed the same amount again, you would owe nothing more in January (because the payments on account covered it), or perhaps a small balancing payment if your income rose.

The practical implication: in year one of Self Assessment, budget to set aside around 150% of your expected tax bill. The extra 50% is not a penalty or a problem — it is just HMRC collecting future tax early. But not knowing about it has caught out a very large number of first-time filers.

Your Self Assessment return covers all sources of income in the tax year. Depending on your circumstances, this may include:

• Employment income — your salary and benefits. Your employer provides a P60 or P45 with the relevant figures.
• Self-employment income — profits from your business (not turnover, but profit after allowable expenses). Keep records throughout the year.
• Rental income — from property you let, after deductible expenses. Mortgage interest relief rules changed significantly in recent years — verify the current rules at GOV.UK.
• Dividends — from shares you hold. Your broker or the company will provide the figures.
• Savings interest — bank and building society interest above the Personal Savings Allowance. Verify the current allowance at GOV.UK.
• Capital gains — if you sold assets (shares, a second property, valuables above the annual exempt amount). Verify the current exempt amount at GOV.UK — it has been reduced significantly in recent years.
• Pension income — if you receive a private pension in addition to the State Pension

Keep records for at least five years after the January filing deadline for the relevant year. HMRC can ask for evidence during this period.

Your Unique Taxpayer Reference (UTR) is a 10-digit number assigned by HMRC when you register for Self Assessment. It appears on all correspondence from HMRC about Self Assessment, including letters confirming your registration.

You can also find it through your Personal Tax Account at GOV.UK.

If you have lost your UTR, you can retrieve it through the Personal Tax Account or by calling the Self Assessment helpline. Do not share your UTR with anyone you do not trust — it identifies you in HMRC's system.

HMRC takes late filing seriously. The penalties escalate the longer you leave it:

• An immediate £100 penalty if you miss the 31 January filing deadline, even if no tax is owed
• After 3 months: £10 per day (up to a maximum of 90 days)
• After 6 months: a further penalty of 5% of the tax due or £300, whichever is greater
• After 12 months: a further penalty on the same basis

Late payment of tax also attracts interest and, for more than 30 days late, a 5% surcharge on the unpaid amount.

If you have a genuine reason for missing the deadline (serious illness, a bereavement, a technical HMRC failure), you can appeal a penalty on reasonable excuse grounds. Not knowing about the deadline is not considered a reasonable excuse.

GOV.UK guidance on Self Assessment penalties.

If your circumstances change and you no longer need to complete a Self Assessment return, you must tell HMRC. If you have been sent a notice to file and do not submit a return, HMRC will issue penalties regardless of whether you owe any tax.

To deregister, contact HMRC through the Self Assessment helpline or through your Personal Tax Account. HMRC will confirm whether they agree you no longer need to file.