National Insurance for Side Hustles: Class 2 vs Class 4

Introduction: The Hidden Tax Trap of the Side Hustle

The UK’s self-employed landscape has shifted dramatically.

With the rise of the gig economy, selling on Etsy, or freelancing after hours, thousands of Britons are inadvertently stumbling into complex National Insurance (NI) obligations without realising it.

Unlike Pay As You Earn (PAYE), where your employer deducts tax and NI before you see your payslip, side hustles operate on a system of trust, estimation, and retrospective payment.

Getting it wrong doesn't just mean a bill; it means penalties, lost pension entitlements, and unexpected cash flow crises.

For the self-employed, National Insurance is not a single levy but a tiered system.

The confusion almost always centres on Class 2 and Class 4 contributions.

Historically, these ran parallel, but recent legislative changes have fundamentally altered the trade-offs.

Understanding the distinction between a flat-rate contribution designed to protect your pension (Class 2) and a profit-linked tax that funds the NHS and state benefits (Class 4) is the single most important financial step for any side hustler in the UK today.

The Fundamental Distinction: Class 2 vs Class 4

To navigate the system, you must first understand what you are paying for.

National Insurance is not just "tax"; it is your ticket to the State Pension and certain contributory benefits.

The rules differ significantly depending on whether you are employed, self-employed, or both.

Class 2: The Pension Protector

Class 2 National Insurance was historically a flat-rate weekly payment for the self-employed.

For the 2024/25 tax year, the rules have solidified into a new structure.

Class 2 is no longer a compulsory payment for those with profits above the Small Profits Threshold, but it remains a critical mechanism for building your National Insurance record.

If your profits are below the Small Profits Threshold (£6,725 for 2024/25), you do not have to pay Class 2.

However, you can choose to pay it voluntarily.

This is a crucial distinction for side hustlers with low profits or those who have gaps in their employment history.

Paying Class 2 voluntarily secures a qualifying year for the State Pension without the heavier burden of Class 4 contributions.

Class 4: The Profit Tax

Class 4 operates as a percentage tax on your taxable profits.

It functions more like Income Tax than a flat-rate insurance premium.

You only pay this if your profits exceed the Lower Profits Limit (£12,570 for 2024/25).

This is often the shock for side hustlers who assume their employment tax covers everything; once your side hustle becomes sufficiently profitable, you are liable for an additional 6% (dropping to 6% from 9% in early 2024) on profits between the Lower and Upper Profits Limits.

Unlike Class 2, Class 4 does not build your pension entitlement.

It is purely a revenue-raising mechanism for the Treasury.

A common misconception is that paying high Class 4 contributions grants you better pension rights; it does not.

You could pay £5,000 in Class 4 and gain zero additional pension credits, whereas paying a small voluntary Class 2 sum secures a full year.

Thresholds, Rates, and Limits for 2024/25

The specific numbers matter.

The interaction between thresholds determines whether you are legally required to pay, or whether you should choose to pay.

Below are the operative figures for the current tax year.

The "Day Job" Interaction: Why Your Employment Matters

Most side hustlers have a primary employment.

This complicates the National Insurance calculation significantly because your employment income and self-employment profits are treated differently for NI, even though they are aggregated for Income Tax.

If you are employed and earning above the Primary Threshold (£12,570 per year) in your day job, you are already paying Class 1 National Insurance.

This grants you your State Pension credit for the year.

Consequently, you generally do not need to pay Class 2 voluntarily, as you are already "credited" for the year via your employment.

However, you are still liable for Class 4 on your side hustle profits if they exceed the Lower Profits Limit.

The danger arises when side hustlers assume their PAYE deductions cover everything.

They do not.

Class 4 is an additional liability on top of the Class 1 paid via employment.

This is often the "hidden tax" that catches successful freelancers off guard, leading to an unexpected bill in January.

The Class 2 Decision: To Pay or Not to Pay?

For side hustlers with profits under £6,725 (the Small Profits Threshold), the decision to pay Class 2 voluntarily is one of the most sophisticated financial planning moves available.

It costs £3.45 per week (£179.40 a year) to purchase a full qualifying year for the State Pension.

To get the full "New State Pension" (currently over £11,500 per year), you need 35 qualifying years.

Each year is worth roughly 1/35th of the pension pot.

If you have gaps in your record—perhaps due to travelling, caring responsibilities, or low profits—paying Class 2 voluntarily is often an incredible return on investment.

However, you must check your National Insurance record via the Government Gateway before paying.

If you already have 35 qualifying years, paying Class 2 is a waste of money.

The "Deemed" Payment for High Earners

There is a final twist for those with profits above the Small Profits Threshold (£6,725) but below the Lower Profits Limit (£12,570).

Since the abolition of mandatory Class 2, these individuals are treated as having paid Class 2 automatically.

They get the State Pension credit for free.

They do not need to physically pay the £3.45/week, nor do they need to pay Class 4.

This is the "sweet spot" for side hustlers—profitable enough to count, but low enough to avoid the Class 4 levy.

Payments on Account: The Cash Flow Killer

While National Insurance is the statutory obligation, the mechanism of payment often causes the most distress.

HMRC operates a system called "Payments on Account" for taxpayers whose combined tax and Class 4 bill exceeds £1,000.

This system is designed to keep the self-employed current with their taxes, but for the uninitiated, it feels like a demand for double payment.

If your side hustle generates a tax and Class 4 bill of £1,500 in January 2025 (for the 2023/24 year), HMRC will ask for that £1,500 plus a "payment on account" of £750 (50% of the bill) towards the 2024/25 year.

You will pay £2,250 in January, and another £750 in July 2025.

This means your first year of high profitability results in paying 150% of your tax bill in a short window.

"Payments on Account are not a penalty; they are an interest-free loan to the Treasury that you are forced to make.

Budgeting for 150% of your calculated liability is the only way to survive the first year of serious side hustle profitability."

Registration and Filing Obligations

You cannot pay Class 2 or Class 4 without registering for Self Assessment.

The registration deadline is strictly 5th October following the end of the tax year in which you earned money.

If you started selling on eBay or freelancing in June 2023, you had until 5th October 2024 to register.

Missing this deadline incurs an automatic late registration penalty, often followed by late filing penalties if the return isn't submitted by 31st January.

The Trading Allowance Filter

Before worrying about Class 2 or Class 4, apply the Trading Allowance filter.

If your gross trading income (turnover, not profit) is under £1,000, you do not need to register for Self Assessment or pay any National Insurance.

The £1,000 allowance covers the income entirely.

However, if your turnover is £1,001, you must register, though you can still claim the £1,000 allowance instead of deducting actual expenses.

This often simplifies the tax return but means you cannot claim expenses to artificially reduce your profit below the Class 4 threshold.

Decision Checklist: Which Class Applies to You?

Use the following checklist to determine your liability status.

This assumes you have already deducted the Trading Allowance or actual expenses to find your "profit" figure.

• ✅ Profits under £1,000: No registration, no NI, no tax.
• ❌ Profits between £1,000 and £6,725: Must register for Self Assessment.

  No compulsory NI.

  Consider voluntary Class 2 (£3.45/week) if you need pension credits.

• ✅ Profits between £6,725 and £12,570: Must register.

  You get free State Pension credit (treated as paying Class 2).

  No Class 4 due.

• ❌ Profits above £12,570: Must register.

  You get free State Pension credit.

  You must pay Class 4 at 6% on profits above £12,570.

• ✅ Also employed earning over £12,570/year: Your job covers pension credits.

  Ignore Class 2.

  Pay Class 4 on side hustle profits over £12,570.

• ❌ Profits above £50,270: Pay Class 4 at 6% up to the limit and 2% above it.

Strategic Trade-offs: Reducing Your Liability

National Insurance is calculated on "taxable profits," not turnover.

This allows for legitimate planning.

Unlike employees who cannot deduct travel or equipment costs from their NI base, the self-employed can.

Expenses vs.

Trading Allowance

About the author: Lucy Davies writes practical UK guidance with a focus on decisions, costs, and common mistakes.