Self assessment tax returns

A self assessment return brings together all your income for one tax year so that HMRC can work out the tax you owe. Preparing one usually means gathering figures for each type of income, such as self-employment, rent, dividends, interest or foreign income, and checking which allowances and reliefs apply. The return then calculates the tax and any National Insurance due, and the first payment towards next year if payments on account apply.

When an accountant does this for you, they normally collect your documents, prepare the return, send you a draft to check and, once you have approved it, submit it to HMRC as your authorised agent. HMRC lets an agent submit returns, make relief claims and discuss returns with HMRC on your behalf.

You must register if you need to complete a tax return and either have not sent one before or did not need to send one for the 2024 to 2025 tax year. Two triggers are clearly set out on GOV.UK: trading income over £1,000, and property income over £2,500.

The people who file are a mixed group. Common examples include:

• company directors who take dividends
• landlords letting a flat or a room
• employees with a side business or freelance work
• people with income from abroad or capital gains to report

GOV.UK's check if you need to send a tax return tool covers the other situations, and it is worth running through it if you are unsure. You must tell HMRC by 5 October after the end of the tax year if you need to file; for 2025 to 2026 that was 5 October 2026.

The paper deadline for 2025 to 2026 has already passed, so most people still to file will do so online. If you want to pay your bill through your tax code instead of in one go, the return has to be in earlier, by 30 December 2026. Our self assessment deadlines guide keeps all the dates in one place.

In your first year with a large bill, January can bring a double hit. As well as paying the tax for the year just ended, you may have to make the first of two advance payments towards the next year. Each payment on account is half of the tax you owed last year, and they are due by midnight on 31 January and 31 July. They can include Class 4 National Insurance.

You do not have to make payments on account if the tax you owed last year was less than £1,000, or if you paid more than 80% of the tax you owed outside Self Assessment, for example through PAYE.

The penalties for filing late build up over time, and are separate from those for paying late. HMRC also charges interest on unpaid tax; late payment interest was set at 7.75% from 9 January 2026 and tracks the Bank of England base rate, so check the current rate on GOV.UK. People who are within Making Tax Digital for Income Tax come under a newer points-based regime instead.

If your affairs are straightforward, for example one source of extra income with few expenses, filing yourself through HMRC's online service is entirely possible and many people do it every year. People tend to use an accountant when they have several types of income, have sold property or shares, have income from abroad, or simply want someone to check their claims. Whoever prepares it, you must check the return and confirm it is correct before it is submitted, because the legal responsibility stays with you.

• What does the fee include, and would extra income such as rent or capital gains cost more?
• Can they confirm the fee and what they will do in writing?
• When do they need your documents to file comfortably before 31 January?
• Are they supervised for anti-money laundering by HMRC or a professional body, as the law requires?
• How will they get your authority to act with HMRC, and will you see a draft before submission?

Fees depend on how many types of income you have. The online accountant Crunch, for instance, lists a standard Self Assessment at £240 +VAT, with a promotional price from £168 +VAT. Local firms set their own prices, and our guide to what a self assessment tax return costs compares published figures.