HMRC tax return registration deadline looming – 7 tips for first-time filers

If you've received untaxed income in 2022-23 and have never filed a tax return before, you need to let HMRC know by 5 October 2023.

This is the deadline for first-time filers to register to use the self-assessment system. While there's no penalty for missing this cut-off date, the tax office could fine you if your tardiness means you end up filing your return late or paying your bill late.

To help, here are our top tips for anyone who is new to the process.

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1. Register as soon as you can

Whether you have a permanent job and make extra cash from a side hustle or you're fully self-employed, if you have any income that you have not already paid UK tax on, you'll need to register with HMRC for self-assessment.

HMRC's guide takes you through the process, and the sooner you do it the better. That's because after registering you will need to wait to receive your 10-digit Unique Taxpayer Reference (UTR) number.

It will take up to 10 working days to arrive if you're in the UK, or up to 21 working days if you're abroad. You will need this to file your first tax return and any others in the future. If you are filing a paper return – due by the end of October – you won't have much time if you leave registering until the eleventh hour.

Once you receive the UTR number, you can go ahead and set up your online tax account, and sign up for self-assessment online. You'll then be posted an activation code within seven working days (21 abroad), which you'll need so you can complete the sign-in process, and finally submit your tax return any time before the deadline.

• Find out more: what is a UTR number?

2. Put the other self-assessment deadlines in your calendar 

Registering with HMRC isn't the only date you need to remember. Make sure you mark the following in your calendar:

• 31 October If you want to file a paper return, make sure you get it to the tax office by Halloween. 
• 31 January You have until midnight on this day to get your online tax return to HMRC. This is also the date you need to pay your bill by, including the first payment on account instalment if you're self-employed.
• 6 April The first day of the new financial year is when any new tax rates and regulations announced in the Chancellor’s Autumn Statement and Spring Budget (usually unveiled in March) will come into force. It's also the first date that you can file your self-assessment for the previous financial year.
• 31 July If you're self-employed and use payments on account, this is the date when the second instalment is due.

3. Get your paperwork together

Before making a start, get together all the relevant documents and information you need to complete the self-assessment form. That includes your P60 form (if you’re employed), relevant receipts and invoices, bills, bank statements, tenancy agreements, student loan statements, and details of any benefits you’ve received.

It's also a good idea to go through your current and savings account statements for the relevant financial year, making a list of all the different places your money is coming from. That way, you'll have a better idea of which income sources you need to declare and which taxes may be due. 

• Find out more: types of savings and investment income

4. Don't forget allowances and expenses

You may be able to reduce your bill to HMRC by claiming various reliefs and allowances when you file your return. This can range from business trips to office running costs such as stationery. 

You can also claim tax relief on the cost of running a business premises, including energy. If your workplace is at home, then you can also claim a proportion of your bills for the time you are working.

The rules around what you can and cannot claim for can as expenses can be confusing, however. If in any doubt, HMRC's website has more information.

There are also tax breaks for higher-rate and additional taxpayers who made Gift Aid declarations when donating to charity, as well as tax relief on pension contributions using self-assessment.

If you’re declaring capital gains – after selling shares or an investment property, for example – you can reduce your tax bill by offsetting any losses made during the financial year you're filing for.

• Find out more: how to fill in a self-assessment tax return

5. Take your time but don't be late

Try not to leave everything until the last minute. If you miss the deadline for filing online, you could face an initial £100 penalty. After three months, this increases to £10 per day (for up to 90 days). Further penalties are triggered if your return is more than six or 12 months late. 

The tax office will also fine you if you don't pay on time. You’ll be charged daily interest from the date the payment was due and there may be further penalties if you're several months late paying your tax bill. Late payment interest is currently set at 7.75%.

There can also be hefty fines for making a mistake. These are usually reserved for people who have deliberately misled the tax office rather than made careless errors, and it's more important that you file on time. You can always correct any errors after submission.

• Find out more: late tax returns and penalties for mistakes

6. Seek help if you need it

If you don't think you can pay by the deadline of 31 January, get in touch with HMRC as soon as possible.

You may be able to set up a Time to Pay arrangement that lets you pay in instalments over an agreed period. You’ll pay interest on anything owed after the deadline, but at a lower rate than the late payment rate.

7. Use the Which? tax calculator

When submit your tax return – which is due by 31 January 2024 – the Which? tax calculator can help you tot up your tax bill, and suggests expenses and allowances that you might have forgotten.

You can declare income from a range of sources, and even use the tool to submit your return directly to HMRC once you're satisfied that everything's been included.

• Find out more: try the Which? tax calculator