January feels a long way off in April. That distance is exactly why so many Self Assessment returns get filed in a fluster on 31 January, with receipts spread across three email accounts and a shoebox. The deadline itself never moves. The work behind it can be spread out — and once it is, filing takes an afternoon rather than a fortnight.

Here is how the tax year actually unfolds, and what is worth doing at each stage.

Why the deadline falls in January

The UK tax year runs from 6 April to 5 April. A return covers one of those years and is due the following January. The 2024/25 tax year ended on 5 April 2025, so the return — and any tax still owed — is due by 31 January 2026.

Most people on Self Assessment also make payments on account: two instalments towards the following year's bill, due on 31 January and 31 July. You are usually asked for them if your bill is over £1,000 and less than 80% of it was collected through PAYE. So January is rarely about one year. Often it is two bills at once.

April to June: the groundwork months

Nothing is due in this window, which is exactly what makes it valuable.

Move tax money out of the current account

If you are a sole trader, work out a rough percentage of each invoice to hold back for tax and National Insurance, and shift it to a separate account the week the money arrives. A rough figure still beats a January shock, and you can adjust it once the real bill is known.

Keep records as you go

HMRC expects records to be kept for at least five years after the 31 January filing deadline. In practice, you want purchase receipts, bank statements, mileage logs, sales invoices, and details of anything else that counts as income — dividends, rental income, savings interest. Filing them monthly takes minutes. Reconstructing them in January takes days.

July: the second payment on account

31 July is the quiet deadline, and the one most often forgotten. It is the second instalment towards the current year's tax, based on your last bill.

If your income has fallen, you can apply to reduce your payments on account. Do it honestly and with figures you could defend. Reduce them too far and HMRC will charge interest on the shortfall, and can add a penalty if a claim is made carelessly or deliberately. If you are unsure whether a reduction is justified, that is a good moment to ask an accountant.

August and September: assemble the numbers

This is where the tax return stops being a form and becomes a set of figures. Spend an evening on it:

• Reconcile the business bank account for the whole tax year, not just the last quarter.
• Total your expenses by category so you can see what is claimable and what is personal spending.
• Note anything unusual: a one-off sale, equipment bought, a pension contribution, a gift of shares.
• Gather third-party figures — dividend vouchers, interest statements, rental summaries — before you need them.

Do this now and you will spot gaps while there is still time to chase a missing statement. Wait until January and the same gap becomes a delay.

5 October: the registration deadline that catches people out

If you started self-employment or began receiving income that needs declaring, you normally have to tell HMRC by 5 October following the end of the tax year in which it started. Missing that date can trigger a penalty for failing to notify, even if no tax turns out to be due.

Registering is not the same as filing. You can register as soon as you start trading and file months later. Plenty of new sole traders assume registering means paying straight away, and delay both.

October to December: filing opens, so use it

The online return for the previous tax year is generally available from early April. Two autumn dates matter:

• 31 October — deadline for filing a paper return.
• 30 December — file online by this date if you want tax owed collected through your PAYE code rather than paid directly. It only applies where the amount is under £3,000 and you file online.

Filing in November or early December is the single biggest favour you can do yourself. Your liability gets worked out while there is still time to check it, query it, and plan the payment rather than find it.

January: filing, paying and the penalty clock

31 January is both the filing deadline and the payment deadline: the balancing amount for the year just reported, plus the first payment on account for the next one.

Late filing penalties build in stages:

• £100 immediately, even if you owe no tax at all.
• £10 a day after three months, capped at £900.
• 5% of the tax due, or £300 if that is higher, at six months.
• The same again at twelve months.

Late payment is charged separately: 5% of the unpaid tax at 30 days, six months and twelve months, plus daily interest. Returning the form late and paying late are two different failures, and both hurt.

One practical tip: if you cannot pay in full, file on time regardless. The filing penalty is automatic, but the payment side can often be managed with a time to pay arrangement agreed with HMRC in advance. Let it sit and the charges stack up.

Make next January uneventful

The people who file calmly are not more organised by nature. They simply close the year early. Set a date in your diary for the first week of May to reconcile the previous tax year, and a second date in early December to file. By then, filing is a case of typing in numbers you already trust.

Keep three things running in the background: a separate tax savings account, a folder for the year's records, and a rough note of anything unusual as it happens. That is the whole system.

Tax rules change and everyone's circumstances differ, so treat this as a map rather than advice for your specific position. If you have multiple income sources, a limited company, or a year with something complicated in it, a bookkeeper or accountant will usually save you more than they cost.

Photo: Nataliya Vaitkevich / Pexels