When Is the Self-Assessment Tax Return Deadline?

Self-Assessment runs on a fixed annual calendar, and the date almost everyone needs to remember is 31 January. That is the online filing deadline, and the same day your tax payment is due. Because the tax year ends on 5 April, the 31 January deadline relates to the year that finished roughly ten months earlier, a lag that catches people out every winter. Our guide to Self-Assessment sets out the full process; here are the dates that matter.

The dates in plain English

If you are filing for the first time, you must register by 5 October following the end of the tax year, so HMRC can issue your Unique Taxpayer Reference in time. If you still prefer paper, the deadline is 31 October, three months earlier than the online cut-off, which is one of the strongest reasons most people now file online. The 31 January deadline is when the online return must be submitted and the tax paid.

Many taxpayers also make payments on account: two advance instalments towards the following year’s bill, each broadly half of the previous year’s tax, due on 31 January and 31 July. They can feel like paying twice in your first year of Self-Assessment, so it is worth budgeting for them in advance. If your income has fallen, you can apply to reduce these payments, but overstating the reduction leaves you with interest to pay, so estimate honestly.

There is one more date to keep at the back of your mind. If you want HMRC to collect a smaller tax bill through your PAYE code, spreading it across the next year’s salary or pension instead of paying a lump sum, you generally need to file online by 30 December, a month earlier than the main deadline. It only applies to bills under £3,000 where you have PAYE income, but for those it can ease the cash-flow squeeze considerably.

It is worth stressing that the £100 penalty is automatic and applies even if you are due a refund or owe nothing at all. HMRC will sometimes waive penalties where you have a genuine “reasonable excuse”, a serious illness or bereavement, say, but simply forgetting, or finding the online system confusing, does not usually qualify. The safest course is always to file first and sort out any payment difficulty afterwards.

Giving yourself breathing room

The single best habit is to file early, well before January, so you know your bill months ahead and can spread the cost. Filing early does not bring the payment date forward; the tax is still due on 31 January. If you genuinely cannot pay, HMRC’s online Time to Pay service can spread smaller bills into monthly instalments. For the bigger picture on staying efficient year-round, see our tax planning hub and personal tax planning guide.

The January rush is largely self-inflicted: millions leave their return until the final week, and predictable problems follow, forgotten passwords, missing figures, and a helpline that is impossible to reach. Gathering your paperwork in April, as soon as the tax year closes, turns a stressful scramble into a quiet hour’s work. It also gives you time to spot any planning opportunities before the deadline rather than after, when your options have narrowed.

One point often misunderstood: filing your return early does not mean you have to pay early. You can submit in May and still hold your money until 31 January, which is the best of both worlds, certainty about the figure, but no loss of the cash in the meantime. Knowing your liability that far ahead also lets you set aside the right amount steadily rather than finding it in a hurry, and to plan any payments on account with confidence.

Remember, too, that the deadlines apply per tax year, so if you have missed previous years you may have several returns and penalties to bring up to date at once. HMRC generally expects outstanding returns to be filed as soon as possible, and interest continues to accrue on unpaid tax throughout. Tackling a backlog promptly, rather than letting it grow, is always the cheaper path.

This is general information, not personal advice, and penalty rules can change. If your return is complex or your income has grown, a qualified accountant or adviser can take the deadline stress off your plate, and Vetted Wealth can match you, free of charge, with an independently vetted, FCA-regulated professional.

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