Self-Assessment First-Year Filing Checklist

The first Self Assessment is much harder than every one after it, because before you can file anything you must register, wait for codes to arrive by post, set up an online account and work out which pages of the return apply to you. None of that can be done in the last week of January. The first bill is often larger than expected too, because payments on account start at the same time. This checklist prevents the costly mistakes.

Register early — the codes come by post

Registration is the step people underestimate. You must register by the October following the end of the tax year in which you started, and the process involves waiting for a Unique Taxpayer Reference and an activation code to arrive in the post. Leaving it until December means racing the deadline with no margin for a lost letter. Register as soon as you are confident you are running a business rather than an occasional hobby.

  • As soon as you start: register with HMRC, and set up a simple record-keeping system separating business from personal spending.
  • Through the year: keep invoices, receipts, bank statements and mileage records as you go, and put money aside for tax in a separate account.
  • Before filing: gather everything for the tax year, check which supplementary pages apply, and file well before the January deadline.

The penalties are automatic and independent of each other. A fixed penalty applies as soon as the filing deadline passes, even where no tax is owed, with daily penalties after three months. Late payment attracts separate charges and interest. Filing on time while arranging to pay is always better than doing neither.

If you cannot pay, contact HMRC before the deadline about a Time to Pay arrangement rather than waiting to be chased.

Registration (by 5 October)

0 of 5 complete

Records to keep (entire year)

0 of 7 complete

Allowable expenses

0 of 10 complete

Filing the return (by 31 January)

0 of 7 complete

Payment

0 of 6 complete

Future planning

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Helpful organisations

HM Revenue & Customs

Government

Responsible for collecting taxes, paying some forms of state support, and administering national insurance.

Visit website0300 200 3300

Frequently asked questions

Why is my first bill so much bigger than I expected?
Because payments on account start at the same time. Once your Self Assessment liability passes a threshold, HMRC asks you to pay towards the following year in advance, in two instalments due in January and July. In your first year that means settling the year just ended and paying half of the next one together, so the January bill can feel like a year and a half of tax at once. Budget for it from the first month of trading.
What can I claim as an expense?
Costs incurred wholly and exclusively for the business — stock, materials, business travel, professional fees, insurance, and a proportion of costs where you work from home. Keep the evidence rather than estimating, because HMRC can ask you to substantiate figures years later. Mixed-use items need apportioning honestly, and there are simplified flat rates for some categories such as mileage and home working. If you are unsure whether something qualifies, ask an accountant rather than guessing generously.
What if I cannot afford to pay the tax?
Contact HMRC before the deadline and ask about a Time to Pay arrangement, which spreads the amount over monthly instalments. HMRC agrees these routinely with people who engage early and can show what they can realistically afford. Interest still accrues but late payment penalties can be avoided. Have your income and essential outgoings ready. File the return on time regardless — filing and paying are separate obligations with separate penalties.
Do I need an accountant?
Not necessarily for a simple sole trader return with straightforward income and expenses. An accountant earns their fee where there is property income, capital gains, foreign income, complex expenses, or a limited company involved, and often identifies claims that more than cover the cost. If you do file yourself, do a dry run well before the deadline so you discover any missing information while there is still time to find it.

Related guides

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Time to Pay Arrangements With HMRC

If you have a tax debt you cannot pay immediately — whether self-assessment income tax, VAT, PAYE, or another HMRC liability — you may be able to agree a Time to Pay (TTP) arrangement with HMRC. A TTP allows you to spread the debt over monthly instalments. HMRC is generally willing to agree TTP if you contact them before enforcement action begins, but defaulting on an agreed plan can have serious consequences.

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Disclaimer

This information is for general guidance only and does not constitute legal, financial, or professional advice. Always check official sources and seek qualified help where needed.