If you're self-employed, a landlord or a company director, Self Assessment is the system you use to tell HMRC about income that isn't taxed at source. Miss a date and the penalties start automatically - so here are the deadlines that matter and how to stay comfortably ahead of them.

The key dates

The UK tax year runs from 6 April to 5 April. For the tax year just ended, the dates to remember are:

  • 5 October - the deadline to register for Self Assessment if it's your first time (for example, your first year of self-employment or as a new landlord).
  • 31 October - the deadline for paper tax returns. Almost everyone files online instead.
  • 31 January - the big one: the deadline to file your online return and pay the tax you owe for the previous tax year.
  • 31 July - the second payment on account falls due, if you make them.

What is a "payment on account"?

If your tax bill is over £1,000, HMRC usually asks you to pay next year's tax in two instalments - one on 31 January and one on 31 July - each based on your previous bill. It catches a lot of people out in their first year, because that January payment can include the full bill plus the first instalment of the next one. Planning for it early is half the battle.

What late filing actually costs

Miss the 31 January filing deadline and HMRC charges:

  • £100 immediately - even if you owe no tax or are due a refund.
  • £10 a day after three months, up to £900.
  • Further penalties of 5% of the tax due (or £300 if greater) at six and twelve months.

Late payment attracts its own penalties and interest on top. It adds up fast - and every penny of it is avoidable.

How to stay ahead

The trick is simple: don't wait for January. Once the tax year ends on 5 April you can file straight away, which means:

  • You know your exact bill up to ten months early and can budget for it.
  • You spread the stress instead of cramming it into one panicked evening.
  • If you're due a refund, you get it sooner.

Good bookkeeping through the year makes this effortless - when your records are current, the return almost writes itself.

Let us take it off your plate

At TaxMag we prepare Self Assessment returns for sole traders, landlords and directors across Nottingham and beyond - accurately, early, and with every allowance claimed so you never overpay. If January fills you with dread, get in touch and we'll make it a non-event.

This article is general information, not tax advice. Rules and thresholds change - for guidance on your own situation, talk to us.