Filing a Self Assessment in the UK

Each year more than 12 million people file their self-assessment tax return. Yet for many, the process feels like a real chore. In this guide, we’ll explore the essentials of Self Assessment, from who needs to file a self-assessment to key deadlines and tips to make the process easier.​

You'll usually need to file a Self Assessment if any of the following apply to you:​

The Self Assessment process is a way for HMRC to calculate your yearly tax liability, accounting for all income sources and any allowable deductions and reliefs.​

Even if you didn't make a profit, you may still need to file a Self Assessment. Losses can often be carried forward and used to reduce future tax bills.​

The UK tax year runs from 6th of April to 5th of April. Following the end of this period, individuals have a period of time to get their records organised and information submitted to HMRC.​

If you’re new to Self Assessment, you must register with HMRC by the 5th of October to receive your Unique Taxpayer Reference (UTR). This is required for submitting your Self Assessment.​

Any tax owed must be paid by 31 January following the end of the tax year.​

If your tax bill is over £1000, you’ll need to make payments on account towards the following tax year (think of it as pre-paying tax).​

First payment on account: 31 January (50% of the previous year's bill)​

Second payment on account: 31 July (remaining 50%)​

Balancing payment: 31 January following the end of the tax year​

If you're new to Self Assessment, your first payment will include 100% of your first year’s tax bill and 50% of your second year’s liability (calculated based on the first year).​

Learn more: Payment on Account​

To receive tax relief, personal pension contributions must usually be made before 5 April.​

This can be an effective way to reduce your tax bill while saving for the future, particularly for higher-rate taxpayers.​

Being organised for the end of the tax year makes filing significantly easier. For Self Assessment, you'll typically need: ​

When filing your Self Assessment, you can claim business-related expenses.​

Some common deductions include:​

The key rule is that expenses must be related to earning that income. Your accountant can help ensure everything claimed is accurate and compliant. ​

You generally have three options:​

Regardless of the option you choose, you’ll need to gather your income details, expense receipts, and any other relevant information (as outlined further up).​

If you choose to file yourself, follow the guided questions on the HMRC website. ​

If you use a registered tax agent or accountant, they’ll have a questionnaire you complete which enables them to complete your Self Assessment. ​

At Beany, our online questionnaire guides you through the process with explanations and space for you to attach any relevant documentation where needed. If you’re using Xero, it’s even quicker as some of our questionnaire is integrated with your Xero file so the data feeds through, reducing the amount of questions you need to answer.​

If you file yourself, HMRC will review your information and let you know how much tax you owe (or if you’re due a refund).​

If you work with an accountant, they will thoroughly review your information, and produce a set of accounts (the Self Assessment and financial statements). If there are any follow-up questions they’ll get in touch. If your accountant does draft accounts as part of their process, they’ll get you to review and approve your accounts before they finalise and file them with HMRC.​

The timeframe depends on a number of factors, from time of year to whether you’re self-filing or using an accountant.​

If you submit via HMRC you’ll typically have your Self Assessment confirmed immediately or within 72 hours.​

With an accountant, it can take 8-14 weeks once you’ve provided all your information. Outside the busy season, it’s often much faster.​

Once your Self Assessment has been finalised, you’ll be informed of the tax owing or whether you’re due a refund.​

If you’re owed a refund, HMRC will deposit the money into your nominated bank account.​

If you owe tax, you’ll receive both a Tax Calculation and a Self Assessment Statement from HMRC outlining what you owe and when.​

Tax obligations vary depending on business structure, whether you’re registered for VAT, and whether you have employees.​

If you’re a company owner, you’ll have Corporation Tax obligations.​

If you have employees, you’ll have additional obligations such as PAYE and National Insurance. ​

If you sell assets during a tax year, you may also have Capital Gains Tax (CGT) to pay.​

We recommend seeking professional advice for your situation to ensure you’re meeting all your compliance obligations.​

If you’ve incurred a loss: Filing a Self Assessment when your business has incurred a loss allows you to carry the loss forward i.e. you’re able to offset the current year’s loss against future profits to reduce your tax liability in the following year, provided you meet certain tests.​

If you weren’t trading: You need to file a nil return to stay compliant. This lets HMRC know that your business is still active, even if you didn’t trade.​

You can usually amend your Self Assessment through HMRC or your accountant. If you’ve forgotten something that HMRC will be able to track back to you or your business, it’s best to correct it before they contact you as penalties may apply if they discover an error first.​

If you miss the filing deadline, HMRC usually applies an automatic £100 penalty. Further penalties may apply if the return remains outstanding: ​

If you file on time but do not pay by the deadline, HMRC may charge interest and apply late payment penalties that increase the longer the balance remains unpaid. ​

If you know you won't be able to pay your tax bill in time, it's important to act early. In many cases, HMRC will allow a Time to Pay arrangement, letting you spread payments over an agreed period. An accountant can help you assess your options and communicate with HMRC if needed. ​

The easiest is via bank transfer, credit/debit card, or setting up a direct debit.​

You can find all the options for paying your Self Assessment tax bill at https://www.gov.uk/pay-self-assessment-tax-bill ​

We work with UK sole traders and company directors/shareholders to make Self Assessment simpler. For companies, we include 2 Self Assessments (for directors/shareholders) as part of our accounting packages. For sole traders, we have a special sole trader package.​

With fixed pricing, clear guidance, and online support, our accountants handle your filing and help you stay compliant with confidence. ​

Get in touch to see how Beany can help with your Self Assessment. ​