Essential tax dates and deadlines every UK side hustler must mark in their diary

Introduction: Why Tax Dates Matter More Than You Think

Running a side hustle in the UK means accepting that HM Revenue & Customs (HMRC) will eventually want a slice of your earnings.

What many new side hustlers underestimate is not the tax itself, but the strict calendar by which it must be paid.

Miss a deadline and you face penalties that can quickly erode the profits you worked hard to earn.

This guide walks through every significant tax date and deadline you need to track, with concrete examples showing how these rules apply to real UK side hustlers.

The good news is that the UK tax system for self-employed individuals follows a predictable rhythm.

Once you understand the cycle, you can build simple habits that keep you compliant without consuming your weekends.

Let's start with the foundation: understanding the UK tax year itself.

The UK Tax Year: Your Temporal Framework

The UK tax year runs from 6 April to 5 April the following year.

This matters because every deadline we'll discuss is anchored to these dates.

For the 2024/25 tax year, for instance, the period runs from 6 April 2024 to 5 April 2025.

All income earned and expenses incurred within these dates must be reported to HMRC.

This differs from the calendar year, which catches many people out when they first start freelancing.

If you earned £2,000 from freelance graphic design in December 2024, that income belongs to the 2024/25 tax year, not 2025.

It won't appear on your tax return until the following January.

Self Assessment: The Central Deadline

The 31 January Cut-Off

If your side hustle earns more than £1,000 in a tax year, you must register for Self Assessment and file a tax return.

The primary deadline is 31 January following the end of the tax year.

This means your 2024/25 tax return (covering 6 April 2024 to 5 April 2025) must be submitted by 31 January 2026.

Here's why this date matters so much: it's not just the filing deadline.

It's also the payment deadline for your Income Tax and your first payment on account.

Miss it and HMRC will start charging penalties immediately.

Penalties for Late Filing

HMRC operates a points-based penalty system for late Self Assessment returns:

• 1 day late: £100 fixed penalty
• 3 months late: Additional £10 per day (up to £900)
• 6 months late: Greater of 5% of tax due or £300
• 12 months late: Greater of 5% of tax due or £1,050

These penalties stack.

A return filed six months late could easily attract penalties exceeding £1,000, regardless of whether you owe any tax.

Interest also accrues on unpaid tax from the deadline.

Payment on Account

Once your tax bill exceeds £1,000 in a year, HMRC will normally require you to make "payments on account" — advance payments toward the following year's tax.

These are split into two instalments:

• First payment on account: 31 January (along with your tax return)
• Second payment on account: 31 July

Each payment is 50% of your previous year's tax bill.

For example, if your 2024/25 tax bill is £1,200, you'll pay £600 on 31 January 2026 and £600 on 31 July 2026, while also paying your 2025/26 first payment on account.

Key Payment Dates Throughout the Year

Beyond the 31 January juggernaut, several other dates demand your attention:

VAT: When Registration Becomes Compulsory

Most side hustlers won't need to worry about VAT initially.

However, if your turnover reaches the threshold, it becomes mandatory.

The current VAT registration threshold stands at £90,000 of taxable turnover over a rolling 12-month period.

Once you cross this threshold, you must register within 30 days.

Even before reaching the threshold, voluntary VAT registration can make sense for some side hustlers — particularly those dealing with business clients who can reclaim the VAT.

However, this requires careful analysis of whether the administrative burden and cash flow implications are worth it.

National Insurance Contributions

As a self-employed side hustler, you'll pay Class 2 and Class 4 National Insurance contributions, both calculated through your Self Assessment tax return.

Class 2 contributions are currently charged at £3.45 per week for profits above the Small Profits Threshold of £6,725 per year.

These count toward your State Pension and other benefits.

Class 4 contributions are charged at 9% on profits between £12,570 and £50,270, then 2% on profits above that.

These are calculated and paid alongside your Income Tax.

"The confusion I see most often among side hustlers is treating National Insurance as optional.

Unlike Income Tax, Class 2 contributions actually purchase benefit entitlements — including your State Pension.

Skipping them to save money means both higher future taxes and reduced retirement income." — Chartered accountant speaking to tax guidance website

The key dates for National Insurance align with Self Assessment: Class 2 and Class 4 payments for 2024/25 are due by 31 January 2026 alongside your Income Tax.

The Trading Allowance and Allowable Expenses

Understanding what you can deduct reduces your tax bill legitimately.

The trading allowance allows you to earn up to £1,000 in gross income without registering for Self Assessment, provided your total self-employment income doesn't exceed £1,000.

Above this, you can either:

• Claim the £1,000 trading allowance as an expense (simpler), or
• Claim actual allowable expenses (potentially more valuable if expenses exceed £1,000)

Allowable expenses include things directly connected to your side hustle: equipment, software subscriptions, a proportion of home office costs, professional insurance, marketing, and professional development.

They do not include personal expenses, the costs of buying goods for resale (these reduce profit differently), or fines and penalties.

Building Your Tax Calendar: A Practical Framework

Rather than trying to remember every deadline in your head, build these habits into your annual routine:

• January: File previous year's tax return.

  Check your payment on account amount.

  Update records for the new tax year.

• April: Verify your record-keeping system is working.

  Check if any expense receipts need organising.

• July: Note the second payment on account due date.

  Check if your income has changed significantly and consider adjusting future payments.

• October: If you started a new side hustle, confirm you've registered for Self Assessment.
• Throughout: Keep digital records of all income and expenses.

  Bank transactions alone are not sufficient — you need descriptions of what each transaction represents for your business.

Common Pitfalls to Avoid

The following mistakes appear repeatedly among UK side hustlers dealing with HMRC:

Assuming no tax is due because no bill arrived. Unlike PAYE employees, self-employed individuals receive no automatic tax calculation.

It's entirely your responsibility to file and pay.

Not receiving a letter does not mean you owe nothing.

Forgetting the payment on account trap. After your first year of Self Assessment, HMRC automatically sets up payments on account.

When your tax bill is higher in subsequent years (because your side hustle grew), the final payment on account in July might not cover the full liability.

Check your statements regularly.

Mixing personal and business finances. HMRC expects clear records.

A bank account used for both weekend eBay selling and family groceries creates extra work come January and raises questions if you're ever investigated.

Underestimating expenses. Many side hustlers forget they're entitled to deduct legitimate business costs.

A graphic designer who bought a new laptop, subscribes to design software, and pays for a co-working space membership has substantial allowable expenses that reduce their tax bill considerably.

Special Cases Worth Noting

Multiple employments with a side hustle. If you're employed PAYE and also run a side hustle, your tax code may be adjusted to collect your side hustle tax through PAYE rather than requiring a full Self Assessment.

However, this only works for simpler situations.

If your side hustle generates significant profit, Self Assessment remains necessary.

Platform economy work. If you drive for Uber, Deliveroo, or similar platforms, the platform may handle your tax affairs through the intermediary model.

However, you remain responsible for ensuring this is correct and for reporting if your circumstances change.

Property income. If your side hustle involves renting property (including spare rooms through schemes like Airbnb), different rules apply.

Property income has its own allowance (£1,000) and different allowable expenses.

This requires a separate section on your Self Assessment return.

Getting Help When You Need It

HMRC's online services through the Government Gateway handle most basic Self Assessment needs adequately.

For straightforward side hustles with simple records, many people file their own returns without difficulty.

The HMRC app also provides useful functionality for checking your tax position.

However, if your side hustle involves complexity — IR35 considerations if you're working through your own company, overseas income, or significant equipment purchases — speaking with a qualified accountant typically pays for itself.

The Institute of Chartered Accountants in England and Wales (ICAEW) and Association of Chartered Certified Accountants (ACCA) maintain directories of members, many of whom specialise in small businesses.

The cost of an accountant for a simple side hustle return typically ranges from £150 to £400 annually, depending on complexity.

For many side hustles generating several thousand pounds, this represents good value for the assurance of accuracy and the time saved.

Summary: Your Essential Calendar

Mark these dates in your diary and you'll never miss a UK side hustle tax obligation:

• 5 April: Tax year ends.

  Any income or expenses after this date belong to the next year.

• 6 April: New tax year begins.

  Start fresh record-keeping if needed.

• 5 October: Register for Self Assessment if you earned over £1,000 in the previous tax year.
• 31 January: The big one.

  File your tax return and pay what you owe.

  Also pay first payment on account for current year.

• 31 July: Second payment on account due.

The rhythm of UK self-assessment becomes manageable once you internalise these dates.

Build reminders two weeks before each deadline, keep digital records throughout the year, and file early rather than waiting until January.

That way, if HMRC has questions about your return, you have time to respond without penalties stacking up.