You need to submit a self-assessment tax return under two circumstances:

In some cases, HMRC will notify you that you are required to submit a tax return depending on the complexity of your tax affairs. Nonetheless, there are circumstances in which you may qualify without having been notified, even as an individual who receives the majority of their taxable income under PAYE. Most commonly, it involves additional untaxed income either from self-employment, if you are liable for capital gains tax from selling property or possessions, savings income and income from investments, foreign income, rental income or property income.

If all your income is taxed, and you have no chargeable gains you may not need to submit one. Nonetheless it is worth checking with HMRC’s online checking tool seeing as there are often unexpected situations where you need to submit a tax return.

Employees may also want to submit under self-assessment even if they made no chargeable gains – they might need proof of income, want to claim an income tax relief or tax refund if you have paid too much tax. Or if you need to provide proof of self-employment to get tax-free childcare or maternity allowance.

If you want to claim income tax relief on employment expenses and they are less than £2,500 then you can do this without submitting a tax return but only by post using form P87. For a guide to allowable expenses see HMRC https://www.gov.uk/tax-relief-for-employees More details and a printable version of P87 can be found here https://www.gov.uk/guidance/send-an-income-tax-relief-claim-for-job-expenses-by-post-or-phone

National Insurance

National Insurance contributions are not handled through a self-assessment tax return; instead, there is a different process for reclaiming any overpaid NI. However, it is unlikely that you have overpaid NI, as this typically occurs only in specific circumstances—such as if you paid NI on two different employments held simultaneously, or if you were both employed and self-employed at the same time.

Tax Code Corrections

If you were taxed the wrong amount because you were assigned an incorrect tax code—perhaps one that didn't properly reflect your annual allowance—this will be corrected by issuing you a new tax code. The new code ensures you pay the correct amount of tax moving forward, and any discrepancies from previous payments will be adjusted accordingly.

Tax Relief on Pension Contributions

In some circumstances you will need to claim tax relief on your pension contributions through self-assessment. You need to make a claim if you pay Income Tax at a rate higher than 20% and your pension provider only claims the basic 20% for you (this is known as 'relief at source'). If your pension scheme doesn't automatically apply tax relief, or if someone else contributes to your pension. Additionally, if you're paying in more than £10,000, you'll need to contact HM Revenue & Customs (HMRC) to claim the tax relief.

High Income Child Benefit

If you or your partner have an individual income over £60,000, you may need to pay the High Income Child Benefit Charge. This applies whether you or your partner receive Child Benefit, or if someone else gets Child Benefit for a child living with you and contributes at least an equal amount towards the child's upkeep. It doesn't matter if the child living with you isn't your own; the charge may still apply.

HMRC Deadlines for Self Assessment Tax Returns

Deadlines for registration and submission of an online return apply to the previous UK tax year which runs from April 6 th – April 5th. For example, the deadline for taxpayers to declare income tax owed from the 2023/24 tax year (06/04/23 - 05/04/24) falls within the 2024/25 tax year.

Registration is due by October 5th , and the precise deadline for submission depends on the type of submission. Paper tax returns must be submitted by 31st October, whilst online tax returns must be made by the 31st of January.  It is expected that paper returns will be phased out, but the Low Incomes Tax Reform Group continues to campaign for them to be supported.

These deadlines would only differ if the notice requesting a self-assessment form was submitted late, in which case the tax-payer would have 2-3 months to respond.

On the 31st of January any remaining tax owed on the previous tax year is due (a balancing payment). In addition, if payment on account takes place, the first instalment is also due. The second payment on account is due on the 31st of July.

Understanding Payments: When will you get the tax bill for each tax year?

Getting your head around when payments are made is not entirely straightforward. People pay on account except for certain circumstances . This means paying instalments of your tax bill ahead of your tax return.

If you were paying on account for the 2023/24 year you would pay instalments toward it in January 2024 and July 2024. On 31 January 2025 you pay your balancing payment for any unpaid tax, plus your first instalment toward the 2024/25 bill.

The first relevant tax year in which you transition to payment on account can be difficult as it involves paying the full amount for the last tax year, and half the estimated amount owed on the current tax year.

There are certain situations in which you can request to not pay on account. For example, you can submit the SA303 form if you expect your income to drop significantly enough that you would be overpaying.

There are a number of payment methods. You can pay via cheque, bank transfer, or debit card for example. In some cases, if people also have income via PAYE, it is possible to pay using a code deduction (reducing your personal allowance). Though note the December 30th deadline for this option). This means gradually deducting your tax bill from your UK income via a tax code.

Ending self-assessment

If your tax position changes and you no longer need to submit a self-assessment tax return, say for example you are no longer self-employed, do not receive enough income, or have left the UK, you can contact HMRC with your UTR (Unique Taxpayer Reference). If HMRC fails to notify you that you do not need to submit a return you should continue to do so, as you may still be liable to late-submission penalties.

Penalties

The penalties for failing to meet self-assessment deadlines are quite strict. A late submission immediately results in a fine of £100. After which an additional £10 per day is added to the bill once the return is 3 months late for up to 90 days. Payments more than 30 days late will have added an additional 5%, rising by 5% after 6 months and again after 12 months. Additionally, there may be interest payments on any tax you owe. Those joining the government making tax digital scheme will face different penalties, more information can be found here .

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