Self Assessment Tax Return: A Guide for the Self-Employed

A Self Assessment tax return is how self-employed people in the UK tell HMRC what they earned and pay the Income Tax and National Insurance they owe. If you made more than £1,000 from self-employment in a tax year, you’ll usually need to file one. The main online deadline is 31 January. This guide is for sole traders and freelancers doing their return — who needs to file, the deadlines, what you need to hand, how to file step by step, and how to avoid penalties.

What is a Self Assessment tax return?

Self Assessment is the system HMRC uses to collect tax on income that isn’t taxed automatically. Employees have Income Tax taken from their wages through PAYE, but self-employed profits, rental income and other untaxed earnings aren’t — so you report them yourself on a tax return.

On the return you declare your income, take off your allowable expenses, and HMRC works out the tax and National Insurance due on your profit. You then pay it by the deadline. The return for a tax year covers 6 April to 5 April.

Do you need to file a Self Assessment tax return?

You’ll normally need to file if you were self-employed and earned more than £1,000 in the tax year. The £1,000 trading allowance covers income below that, so you may not need to report it.

There are other reasons you might need to file too — for example untaxed income, rental income, higher earnings, or claiming certain reliefs. If you’re newly self-employed, you’ll need to register as a sole trader first to get into the system.

Self Assessment deadlines

Missing a deadline triggers an automatic penalty, so these are the dates to keep. Using the 2025-26 tax year as an example:

Most people file online, which gives you until 31 January. If you want HMRC to collect the tax through your tax code, you need to file by 30 December instead.

What you need before you start

Filing is far quicker if you gather everything first. You’ll usually need:

• Your Unique Taxpayer Reference (UTR) and Government Gateway login
• Your National Insurance number
• Records of your self-employed income for the year
• Your allowable business expenses and receipts
• Details of any other income — employment (P60 or P45), bank interest, dividends, pensions or rental income
• Records of anything you want to claim, such as pension contributions or Gift Aid

Keeping tidy records through the year makes this the easy part. Our sole trader bookkeeping guide covers a simple routine, and the Accounteezy bookkeeping tool can help you keep income and expenses in order.

How to file your Self Assessment tax return, step by step

1. Register and get your UTR if this is your first return — do this well before the deadline, as the UTR arrives by post.
2. Gather your income and expense records for the tax year.
3. Sign in to your HMRC online account with your Government Gateway details.
4. Complete the main return (SA100) and the self-employment pages (SA103) for your business.
5. Enter your income and allowable expenses, plus any other income and reliefs.
6. Check HMRC’s calculation of the tax and National Insurance you owe.
7. Submit by 31 January and pay what you owe by the same date.

You can file directly through HMRC’s online service or use commercial software. Whichever you use, submit early if you can — leaving it to late January is when mistakes happen.

How your tax bill is worked out

You pay Income Tax on your profit — your income after allowable expenses — not on everything you earned. The first £12,570 is usually covered by the personal allowance, then Income Tax applies at the basic, higher and additional rates depending on your total income.

On top of that you’ll usually pay Class 4 National Insurance: for 2026-27 that’s 6% on profits between £12,570 and £50,270, and 2% above £50,270. Class 2 National Insurance is generally treated as paid rather than charged. All of it is collected through your Self Assessment return.

Payments on account

If your tax bill is over £1,000, HMRC usually asks for payments on account — advance payments towards next year’s bill. You make two, each half of last year’s tax, due on 31 January and 31 July. They don’t apply if last year’s bill was under £1,000, or if more than 80% of your tax was already collected at source. If your income drops, you can ask HMRC to reduce them.

Penalties for filing or paying late

HMRC charges penalties automatically, even if you owe no tax. For filing late:

• The day after the deadline: a £100 fixed penalty
• 3 months late: £10 a day, up to a maximum of £900
• 6 months late: a further 5% of the tax due, or £300 if greater
• 12 months late: another 5% or £300, whichever is greater

Paying late brings its own charges: 5% of the unpaid tax at 30 days, 6 months and 12 months, plus interest on what you owe. Filing on time and paying what you can is always cheaper than ignoring it.

Self Assessment and Making Tax Digital

How self-employed people report is changing. From April 2026, sole traders and landlords with qualifying income over £50,000 move to Making Tax Digital for Income Tax — keeping digital records, sending quarterly updates and making a final declaration that replaces the usual return. The threshold falls to £30,000 from April 2027 and £20,000 from April 2028. If that’s you, getting your bookkeeping digital now will make the switch straightforward.

Tips to make Self Assessment easier

• Keep records through the year rather than scrambling in January
• Use a separate bank account for business so nothing gets missed
• Set aside a share of each payment for your tax bill
• Claim every allowable expense so you don’t overpay
• File early — you’ll know your bill sooner and avoid the deadline rush

Frequently asked questions

Do I need to file if I earned under £1,000?

Usually no. The £1,000 trading allowance means gross self-employed income up to £1,000 doesn’t need to be reported. Once you go over £1,000, you need to register and file a return.

When is the Self Assessment deadline?

The online return and payment are due by 31 January following the end of the tax year. Paper returns are due earlier, by 31 October, and you must register by 5 October if it’s your first time.

How much tax will I pay?

You pay Income Tax on your profit above the personal allowance, plus Class 4 National Insurance at 6% on profits between £12,570 and £50,270 (2% above). The exact amount depends on your total income for the year.

What happens if I file late?

You get an automatic £100 penalty the day after the deadline, even if you owe nothing. Further penalties build up at 3, 6 and 12 months, and paying late adds more charges plus interest.

Can I file my own tax return?

Yes. Many sole traders file their own return online through HMRC. If your situation is more involved or you’d rather be sure it’s right, an accountant or bookkeeper can prepare and file it for you.

What records do I need?

Records of your income and allowable expenses with receipts, plus any other income such as employment or interest. Keep them for at least five years after the 31 January deadline.

Do I still file Self Assessment under Making Tax Digital?

Once you’re in Making Tax Digital for Income Tax, quarterly updates and a final declaration replace the usual return. Until you’re mandated, you carry on filing Self Assessment as normal.

This guide provides general information and does not replace advice based on your individual circumstances. Tax rules, rates and thresholds can change, so check current GOV.UK guidance or ask a qualified adviser before you file.