Every year, hundreds of thousands of UK sole traders and small business owners face the same sinking feeling in January: the Self Assessment deadline is days away, receipts are scattered across three email inboxes and a carrier bag, and HMRC's website seems to be moving at the speed of dial-up. It doesn't have to be like this. The 2025/26 tax year follows a predictable rhythm of deadlines, and if you know exactly what's coming — and when — you can plan ahead, avoid automatic penalties, and even reduce your tax bill by claiming every allowable expense. This checklist covers every critical date, what you need to prepare, and the traps that catch out even experienced self-employed people.
Key ITSA Deadlines for the 2025/26 Tax Year at a Glance
The UK tax year runs from 6 April to 5 April, so the 2025/26 tax year covers 6 April 2025 to 5 April 2026. Here are the dates that matter:
- 5 October 2025 — Deadline to register for Self Assessment if you became self-employed during the 2024/25 tax year and haven't registered before.
- 31 October 2025 — Deadline for paper Self Assessment returns for the 2024/25 tax year.
- 30 December 2025 — Deadline to submit your 2024/25 online return if you want HMRC to collect tax owed (under £3,000) via PAYE coding adjustment — useful if you also have employment income.
- 31 January 2026 — The big one. Deadline for online Self Assessment filing and payment of any tax owed for 2024/25, plus the first Payment on Account for 2025/26.
- 31 July 2026 — Second Payment on Account for 2025/26.
Miss any of these and HMRC acts immediately. The moment 31 January passes without a filed return, an automatic £100 penalty lands in your account — whether you owe any tax or not. After three months, daily £10 charges begin. After six months, a further 5% surcharge on the tax owed is added. The costs compound quickly.
Who Needs to File a Self Assessment Return?
Not everyone trading under their own name needs to file, but the criteria are broader than many people assume. You must register and file if, in the 2024/25 tax year, you:
- Were self-employed as a sole trader and earned more than £1,000 before expenses (the trading allowance threshold).
- Were a partner in a business partnership.
- Had untaxed income — such as rental income, dividends, or savings interest — above the relevant allowance.
- Earned over £100,000 in total income (regardless of employment status).
- Had to pay the High Income Child Benefit Charge (if your adjusted net income exceeded £60,000).
- Received income from abroad or are a non-domiciled UK resident.
If you stopped being self-employed during 2024/25, you still need to file a return for that year and notify HMRC that your Self Assessment requirement has ended — otherwise they'll keep expecting returns indefinitely.
Building Your Pre-Deadline Checklist: What to Gather
The January crunch is almost always caused by poor record-keeping during the year, not genuine complexity. Here's what you need to have ready well before 31 January 2026:
- Income records — All invoices raised, sales receipts, and bank statements for the period 6 April 2024 to 5 April 2025. If you use cash accounting (permitted for sole traders with turnover under the VAT threshold), record when money was actually received.
- Allowable expenses — Office costs, travel (excluding ordinary commuting), stock and materials, marketing, professional fees, phone and broadband used for business, and relevant training costs. Keep every receipt; HMRC can request evidence up to five years after the filing deadline.
- Mileage logs — If you use your own vehicle for business, log every business journey. HMRC's approved mileage rate is 45p per mile for the first 10,000 business miles, then 25p per mile thereafter.
- Bank statements — Both business and personal if you don't operate a dedicated business account (though having one makes reconciliation far simpler).
- P60 or P45 — If you also had employment income during the year.
- Pension contributions — Any personal pension payments may be eligible for tax relief.
- Capital Gains — If you sold property, shares, or business assets during the year.
Tools like BizHub365 make this process significantly less painful. Its AI-powered receipt scanning captures expense data the moment you snap a photo, and the bank statement import automatically categorises transactions throughout the year — so when January arrives, the heavy lifting is already done rather than just beginning.
Understanding Payments on Account: The Trap That Catches New Sole Traders
Payments on Account are advance payments towards your next year's tax bill, and they trip up a surprising number of people in their second year of self-employment. Here's how they work:
If your Self Assessment tax bill for 2024/25 is more than £1,000 and less than 80% of it was collected at source (e.g. via PAYE), HMRC requires you to make two advance payments towards your 2025/26 bill. Each payment is 50% of your previous year's tax liability, due on 31 January 2026 and 31 July 2026 respectively.
Consider a practical example. Suppose your 2024/25 tax bill is £4,000. On 31 January 2026 you'll owe that £4,000 plus a £2,000 first Payment on Account — a total of £6,000. Many new sole traders are blindsided by this. The solution is to set aside roughly 25–30% of every invoice payment into a separate savings pot throughout the year. It's not glamorous advice, but it is the single most effective way to avoid a cash-flow crisis in January.
If your income drops significantly year-on-year, you can apply to reduce your Payments on Account via your HMRC online account or your Self Assessment return. Just be accurate — if you underpay, HMRC charges interest on the shortfall.
MTD for ITSA: Why 2025/26 Is the Year to Get Ready
Making Tax Digital for Income Tax Self Assessment (MTD for ITSA) is the most significant change to how self-employed people report income in a generation. From April 2026, sole traders and landlords with qualifying income over £50,000 must use HMRC-compatible software to keep digital records and submit quarterly updates — replacing the annual Self Assessment return for that income.
Those with income between £30,000 and £50,000 follow in April 2027, with smaller earners expected to be mandated from April 2028. The 2025/26 tax year is therefore your preparation window. Using MTD-compatible software now means you won't be scrambling to change systems under a legal deadline. BizHub365 connects directly to HMRC's API — meaning quarterly submissions, VAT returns, and eventually ITSA filings can all be sent without bridging software or manual uploads.
Even if you fall below the current MTD threshold, voluntarily moving to quarterly digital record-keeping this tax year gives you cleaner accounts, fewer January surprises, and a genuine head start when the mandate reaches your income band.
Conclusion: Get Ahead of the Deadlines Now
The 2025/26 Self Assessment cycle has a clear rhythm. Register by October if you're newly self-employed. Gather your records progressively through the year rather than in a panic every January. Budget for Payments on Account so they don't ambush your cash flow. And start treating MTD for ITSA as an opportunity rather than a burden — quarterly digital records genuinely do make running a business easier.
Deadlines are unforgiving, but they're also completely predictable. With the right habits and the right tools in place from the start of the tax year, 31 January 2026 can be just another Wednesday rather than the most stressful day of your year.