Who needs to file

You generally need to complete a Self Assessment return if any of the following applied in the tax year: you were self-employed as a sole trader earning more than £1,000; you were a partner in a business partnership; you had untaxed income such as rental income, savings, investments or dividends above the relevant thresholds; or you needed to pay the High Income Child Benefit Charge. Being a company director often means filing too, depending on your income. If you're not sure, check with HMRC.

Registering and the 5 October deadline

If it's your first time, you have to register for Self Assessment before you can file. The deadline to register is 5 October following the end of the tax year you need to report — so for income in the 2025/26 tax year, that's 5 October 2026. Registering gives you your Unique Taxpayer Reference (UTR) and access to file, and it can take a little while to come through, so register well before the deadline.

The key deadlines

Once you're registered, the dates that matter each year are:

  • 31 October — deadline for a paper tax return.
  • 31 January — deadline for an online tax return, and the date any tax you owe for the year must be paid.
  • 31 July — the second "payment on account" is due, if you make them.

So for the 2025/26 tax year, an online return and the balancing payment are due by 31 January 2027. Most people file online, which gives you the extra three months over the paper deadline.

Payments on account

If your tax bill is above a certain level, HMRC asks you to pay towards next year's bill in advance, in two instalments — one on 31 January and one on 31 July — each usually half of your previous year's bill. In your first year you can face your first full bill and your first payment on account together in January, so budget for both.

What you'll need

To fill in the return you'll typically need your UTR and Government Gateway login, records of your self-employed income and allowable expenses, any employment income and P60/P45, details of savings, dividends, rental income, pension contributions and Gift Aid, and any other income. Keeping these records up to date through the year with bookkeeping software makes the return quicker to complete.

Penalties for filing or paying late

Miss the filing deadline and there's an immediate £100 penalty, even if you owe no tax, with further daily and percentage-based penalties the longer it drags on. Late payment attracts interest and additional charges on top.

Making Tax Digital for Income Tax

From April 2026, Making Tax Digital for Income Tax starts to replace the annual return with quarterly digital updates for sole traders and landlords over certain income thresholds. If that applies to you, check your start date and what you need to send.

Having us file your return

Many people file their own Self Assessment. If you are not confident you are claiming everything, or your affairs have become more complex, we can prepare and file the return for you. Get in touch to arrange it.