The UK tax year ends on 5 April. The online filing deadline is the following 31 January. That gap — nearly ten months — is generous enough that most sole traders use roughly the last three days of it.
That would be fine if the work were simply data entry. It is not. The gap matters because the records that make a return straightforward have to be created during the year, and by January the raw material for several of them no longer exists.
Here is what to keep, organised by when it has to happen.
Keep throughout the year
Every business purchase, with the receipt. Date, supplier, amount, what it was for. The receipt image matters as much as the figure; HMRC can ask you to support what you have claimed, and a bank statement line shows that money moved, not what it bought.
The business-use split on anything shared. Phone, broadband, vehicle, a laptop used for both work and home. Record the percentage and how you arrived at it, at the time. This is the single record most often missing in January, because the basis for the split is a judgement made in the moment and is not recoverable afterwards.
Mileage, if you claim it. Date, journey, purpose, miles. HMRC's simplified mileage rates are an alternative to claiming actual vehicle running costs, and the two methods generally do not mix for the same vehicle. A mileage log written weekly is credible; one assembled in January from a calendar is visibly reconstructed.
Home working. Either the simplified flat rate based on hours worked from home per month, or a proportion of actual costs. If you use actual costs, you need the bills and the apportionment basis — rooms used, floor area, or hours.
Anything you are unsure about, flagged rather than guessed. A column marking a row for review turns an hour of January archaeology into a ten-minute conversation.
Keep as it arrives
Certain documents appear once and are easily lost because they do not feel like receipts:
- Annual insurance schedules, including professional indemnity and public liability
- Accountancy and professional fee invoices
- Equipment purchase invoices, with serial numbers where relevant
- Finance or lease agreements, not just the payment records
- Subscription renewal invoices, particularly annual ones
Download these the week they arrive. The common failure is an invoice that only ever existed inside a supplier portal you have since stopped using.
Dates worth knowing
| Date | What happens |
|---|---|
| 5 April | Tax year ends |
| 6 April | New tax year begins |
| 31 July | Second payment on account due, if applicable |
| 5 October | Deadline to register for Self Assessment if newly self-employed |
| 31 October | Paper return deadline |
| 31 January | Online return deadline, plus balancing payment and first payment on account |
The 5 October registration deadline catches people in their first year. It is for registering, not filing, and missing it is a separate problem from missing the January date.
The cash basis question
Most sole traders below the relevant turnover threshold can use the cash basis — income counted when received, expenses when paid — rather than traditional accruals accounting.
This is worth a decision rather than a default, because it changes which records matter. On the cash basis, the payment date drives everything, so your records need payment dates to be accurate and your year-end position depends on what actually cleared by 5 April. On accruals, the invoice date drives it, and you need to track what was owed and owing at the year end.
Whichever you use, apply it consistently and note which one you are on somewhere in the sheet. Switching between them informally across a year produces a return nobody can reconcile.
Record retention
Keep records for at least five years after the 31 January submission deadline of the relevant tax year — longer in some circumstances, such as a late return. Digital copies are acceptable; the practical requirement is that they remain legible and complete.
This is an argument for cloud storage over a shoebox, and specifically for storing the image alongside the row rather than in a separate folder structure you will reorganise twice in five years. A link from the row to the image means the evidence travels with the record.
A December dry run
Here is the single change that makes January painless, and it costs an hour.
In the first week of December, prepare the return as if you were filing it. Not to submit — to find out what is missing while suppliers are still contactable, portals still have your login, and you still remember what the March taxi was for.
The dry run typically surfaces three or four things: a missing annual invoice, a shared-use percentage never recorded, a handful of uncategorised rows, and at least one transaction nobody can identify. All four are solvable in December. In the last week of January, two of them are not.
Keeping the record current
The practical bar is capture within a few days, while the purpose is still obvious. Scanning the receipt as you get it — Scan2Sheet extracts supplier, date, amount, and VAT where shown, and links the image to the row — removes the part that gets deferred, leaving you the business-purpose note and the use percentage, which are the two things only you can supply.
Then spend ten minutes a week on uncategorised rows. A week-old transaction is a memory; a nine-month-old one is a guess with a receipt attached.
Put the December dry run in your calendar now, while it is still months away and therefore still easy to agree to.