Self Assessment Deadlines for Trade Businesses — Key Dates, Payments and Penalties (2026)

The Tax Year — and Which Return Covers What

The UK tax year runs from 6 April to 5 April the following year, not the calendar year. So the 2024–25 tax year covers income earned between 6 April 2024 and 5 April 2025. That return must be filed online by 31 January 2026. The deadline always falls in the January after the tax year ends — you get roughly ten months after the year closes to file and pay.

This lag trips people up. By the time you're filing in January 2026, you're reporting on work you did up to nine months earlier. That's why keeping your books current through the year matters: scrambling to reconstruct twelve months of invoices and receipts in late January is how mistakes and missed expenses happen.

The Key Dates You Cannot Miss

5 October — Register for Self Assessment

If you became self-employed during the 2024–25 tax year and have never filed a return before, you must register with HMRC by 5 October 2025. Registration gets you a Unique Taxpayer Reference (UTR) and access to file online. Leave it late and your activation code may not arrive in time to file by January — HMRC posts it, and it can take a couple of weeks. Register the moment you start trading rather than waiting; there is no downside to being early.

31 October — Deadline for Paper Returns

If you file on paper rather than online, your return for 2024–25 is due by midnight on 31 October 2025 — three months earlier than the online deadline. Almost no trade business needs to file on paper, and the earlier cut-off is a strong reason not to. File online and you get the full extra three months.

31 January — Online Filing, Balancing Payment and First Payment on Account

This is the big one. By midnight on 31 January 2026, three separate things are due:

• Your online tax return for the 2024–25 tax year.
• The balancing payment — the tax and Class 4 National Insurance you owe for 2024–25, less anything already paid via payments on account.
• Your first payment on account toward the 2025–26 tax year (more on these below).

Three obligations, one date. Missing it triggers penalties on the filing and interest plus penalties on the payment — they are assessed separately, so a late January return can cost you twice.

31 July — Second Payment on Account

Your second payment on account toward 2025–26 is due by 31 July 2026. This is the mid-year instalment that many traders forget about because there's no return to file alongside it — but the money is still due, and late-payment interest applies if you miss it.

Payments on Account — the First-Year Trap

Payments on account are advance payments toward next year's tax bill. HMRC assumes you'll earn roughly the same again, so it asks you to pay this year's liability in two instalments before that year's return is even due. Each payment on account is 50% of your previous year's tax bill, paid on 31 January and 31 July.

Here's where new traders get hurt. In your first year of self-employment, your 31 January bill includes the whole of your first year's tax (the balancing payment) plus the first 50% payment on account for the next year. That's effectively 150% of your first year's tax due in one go. A trader who owed £4,000 for the year suddenly faces a £6,000 January bill — and nobody warned them. This single surprise is the most common cash-flow crisis among first-year sole traders.

Payments on account are not triggered if your last tax bill was under £1,000, or if more than 80% of your tax was already collected at source (for example through PAYE on employment alongside your trade).

If your income has dropped — a quiet year, an injury, a slowdown in work — you can apply to reduce your payments on account through your online account or form SA303. Be careful though: if you reduce them too far and end up owing more than you paid, HMRC charges interest on the shortfall. Reduce based on a realistic forecast, not wishful thinking.

Penalties for Filing Late

Late-filing penalties are automatic and escalate the longer you leave it. The structure works like this (always confirm the current figures on GOV.UK, as HMRC updates them):

• 1 day late: an automatic £100 penalty, even if you owe no tax or have already paid.
• 3 months late: £10 per day on top, for up to 90 days — a maximum of £900.
• 6 months late: a further penalty of £300 or 5% of the tax due, whichever is higher.
• 12 months late: another £300 or 5% of the tax due, whichever is higher — and in serious cases, considerably more.

Leave a return a full year and the penalties alone can exceed £1,600 before you've paid a penny of actual tax. The £100 charge applies even on a nil return, so file on time even if your trade made a loss.

Penalties and Interest for Paying Late

Paying late is penalised separately from filing late. On top of interest charged daily from the due date (HMRC's rate tracks the Bank of England base rate plus a margin), late-payment penalties apply at milestones:

• 30 days late: a penalty of 5% of the unpaid tax.
• 6 months late: a further 5%.
• 12 months late: another 5%.

Interest runs the whole time the tax is outstanding, so the cost compounds. Check the current rate and percentages on GOV.UK before relying on these figures — interest rates in particular move with the base rate.

Reasonable Excuse and Appeals

If you miss a deadline because of something genuinely outside your control, you can appeal a penalty by claiming a reasonable excuse. HMRC accepts things like a serious illness, a bereavement close to the deadline, a fire or flood that destroyed your records, or HMRC online service failures. What it does not accept: "I forgot", "my accountant let me down", "I found the system too difficult", or simply not having the money. If you have a valid reason, appeal promptly — usually within 30 days of the penalty notice — and you must put things right as soon as the excuse no longer applies.

Can't Pay? Set Up Time to Pay

If you've filed your return but genuinely can't afford the bill, do not just miss the payment. HMRC offers a Time to Pay arrangement that lets you spread the cost over monthly instalments. For Self Assessment debts under a certain threshold you can often set this up yourself online without phoning, provided your returns are up to date and you apply within 60 days of the payment deadline. Interest still accrues on the outstanding balance, but agreeing a plan protects you from the worst late-payment penalties and from enforcement action. The key is to act before the deadline, not after.

Making Tax Digital Is Changing the Rules

From April 2026, Making Tax Digital for Income Tax (MTD for ITSA) begins phasing in for self-employed people and landlords with qualifying income above a threshold. Instead of one annual return, affected traders will keep digital records and submit quarterly updates through compatible software, with a final declaration after the year ends. The thresholds and timing are being rolled out in stages, so check GOV.UK to see whether and when it applies to your turnover. If you already keep your books digitally through the year, the transition is far less painful than for someone reconstructing a shoebox of receipts each January.

Practical Tips for Tradespeople

• Register early. The moment you start trading, register for Self Assessment. Waiting until the 5 October deadline risks your UTR and activation code not arriving in time.
• File early, even if you pay in January. Filing your return in, say, May tells you exactly what you owe eight months ahead of the payment date — so you can plan for it. Filing early does not bring the payment deadline forward.
• Put money aside as you earn. Move 25–30% of every payment into a separate tax savings pot. When January comes, the balancing payment and the payment on account are already covered — no scramble, no Time to Pay, no panic.
• Track income and expenses through the year. Logging jobs, invoices and material costs as you go means your return is mostly done before you sit down to file. Trade2Base records every job's income and costs in one place, so when Self Assessment season arrives your figures are already there and the tax bill is no surprise.
• Keep records for six years. HMRC can ask to see them, and good records protect you in any enquiry.

Quick Reference: Self Assessment Key Dates 2026

Figures and rates shown here are a guide — penalty amounts, interest rates and Making Tax Digital thresholds change, so always confirm the current numbers on GOV.UK or with an accountant before you rely on them.