Going self-employed feels great until you discover Class 4 NI, payments on account, and HMRC's January deadline. See exactly what you owe, what you keep, and what to set aside before HMRC asks for it.
If you are self-employed in the UK as a sole trader, you pay tax on your profits, not your income. Profit means your gross income (everything you invoiced or were paid for) minus your allowable business expenses (everything you spent legitimately on the business). HMRC does not care about your turnover, only your profit.
The tax bands work the same as for employees, but you pay Class 4 National Insurance instead of the employee 8 percent NI. Class 4 NI is 6 percent on profits between £12,570 and £50,270, then 2 percent above. Crucially, Class 2 NI was effectively abolished from April 2024, so most self-employed people no longer pay it. You only pay Class 2 voluntarily now if you want to maintain your State Pension contribution record below the small profits threshold.
The first £12,570 of profit is tax-free thanks to your personal allowance. Above that, you pay 20 percent income tax up to £50,270, 40 percent up to £125,140, and 45 percent above. The personal allowance tapers from £100,000 onwards (the "tax trap"). All the same rules as PAYE apply, just paid annually through Self Assessment rather than monthly through payroll.
The Trading Allowance lets you earn up to £1,000 per year of self-employed income tax-free, with no need to register with HMRC, file Self Assessment, or keep records. This is genuinely useful for casual side income: occasional eBay selling, a small Etsy shop, freelance writing on the side. Below £1,000, you owe nothing.
Above £1,000, you have a choice. You can either deduct your actual business expenses from your gross income (the standard method), or you can use the £1,000 Trading Allowance instead of expenses. The Trading Allowance approach is simpler (no expense records needed) but only beneficial if your real expenses are below £1,000. For most service-based side hustles with low costs (writing, tutoring, design), the Trading Allowance often saves both time and money.
You cannot mix and match. For each tax year you choose either expenses OR Trading Allowance, not both. If you expect expenses to grow as your business expands, switch to actual expenses once they exceed £1,000.
HMRC's rule is that an expense must be "wholly and exclusively" for the business to be deductible. The most common allowable categories are: office costs (stationery, phone bills, broadband used for business), travel (vehicle costs at 45p per mile for first 10,000 miles, then 25p, plus public transport, accommodation, parking), clothing (uniforms and protective gear only, not normal clothes you happen to wear to work), staff costs, professional fees (accountant, solicitor, professional memberships), insurance, marketing and advertising, and subscriptions to relevant trade journals.
If you work from home, you can either claim a flat rate based on hours worked (£10/month for 25-50 hrs, £18 for 51-100 hrs, £26 for 101+ hrs) or a proportion of your actual home costs (a fraction of council tax, energy, broadband, and rent or mortgage interest based on the percentage of your home used for work). The flat rate is simpler. The actual cost method is usually more generous for serious home-based businesses.
Common items you cannot claim include: meals you eat alone (only allowed when travelling overnight), normal clothing, fines and penalties, your own salary (sole traders take "drawings" from profit, not salary), and entertaining clients (specifically disallowed even for businesses). When in doubt, the question is whether someone could plausibly use the item personally. If yes, it usually is not deductible.
The single most common shock for newly self-employed people is Payments on Account. Once your tax bill exceeds £1,000 in a year, HMRC requires you to make two advance payments toward next year's tax bill, due 31 January and 31 July. Each payment is half of your previous year's tax liability.
The maths is brutal in your second year. Imagine you owe £6,000 of tax for the 2024/25 tax year. By 31 January 2026, you must pay: £6,000 (the actual 2024/25 tax) plus £3,000 (first payment on account for 2025/26), totalling £9,000. Then on 31 July 2026, you owe another £3,000. Many sole traders do not budget for this and end up scrambling to cover a 50 percent larger bill than expected.
The good news: if your income drops in the next year, the payments on account are larger than necessary, and HMRC refunds the difference when you file the return. You can also apply to reduce payments on account if you know in advance your profits will be lower. The system levels out after the first year, but the initial cash flow shock catches almost everyone unprepared.
The most reliable strategy for self-employed cash flow is to transfer a percentage of every payment received into a separate tax savings account, automatically. This avoids the January panic when HMRC's bill arrives.
The right percentage depends on your profit level. Below the higher rate threshold (around £50,270 of profit), set aside 25 to 30 percent covers income tax plus Class 4 NI. Between higher rate and additional rate, set aside 35 to 42 percent. In the £100k tax trap zone, set aside 50 to 55 percent due to the personal allowance taper. Add the appropriate student loan rate (9 percent or 6 percent for postgrad) if applicable.
The simplest implementation is opening a separate savings account labelled "Tax", and setting up an automatic transfer of the agreed percentage every time a client pays you. Some banks (like Mettle and Starling) and accounting tools (FreeAgent, Coconut) offer "tax pots" that automate this entirely, calculating the right amount based on your profit so far.
Self-employed people miss out on workplace pensions, but pension contributions remain one of the most powerful tax breaks available. Every £1 you pay into a Self Invested Personal Pension (SIPP) is grossed up by HMRC at 20 percent automatically. Higher rate taxpayers reclaim a further 20 percent through Self Assessment. Additional rate taxpayers reclaim 25 percent.
The maths is striking. A higher rate self-employed person paying £8,000 into a SIPP gets £10,000 in the pension after basic rate top-up, then claims back £2,000 through Self Assessment. So £8,000 net cost results in £10,000 pension growth, a 25 percent immediate return before any investment growth.
The annual pension allowance is £60,000 (or 100% of earnings if lower). Contributions also reduce your taxable profit, often pulling income out of higher tax bands or out of the £100k tax trap entirely. SIPPs from PensionBee, AJ Bell, Vanguard, InvestEngine, and Hargreaves Lansdown are easy to open and run alongside any State Pension you build through NI contributions.
Three concrete moves. One: open a separate business bank account if you have not already. Mixing personal and business transactions makes Self Assessment a nightmare and creates HMRC audit risk. Free options include Starling, Mettle, and Tide. Mettle and NatWest also include free FreeAgent accounting software, saving £30 per month.
Two: set up a tax pot or savings account labelled "Tax". Transfer 25 to 30 percent of every payment received automatically. By January, the money is there for HMRC, no scrambling required. The percentage may need to be higher for higher rate taxpayers.
Three: register for Making Tax Digital readiness if your turnover is approaching £50,000. From April 2026, sole traders with turnover above £50,000 must keep digital records and submit quarterly updates to HMRC. From April 2027, the threshold drops to £30,000. Modern accounting software (FreeAgent, QuickBooks, Xero) is already MTD-compatible, so adopting it now avoids painful migration later.
Self-employed people in the UK pay income tax (20% above £12,570, 40% above £50,270, 45% above £125,140) plus Class 4 National Insurance (6% on profits between £12,570 and £50,270, then 2% above). Class 2 NI was effectively abolished from April 2024, so most sole traders no longer pay it. The total effective tax rate for someone earning £40,000 of profit is around 22 percent. For £60,000 of profit, around 28 percent. For £100,000, around 35 percent.
The £1,000 Trading Allowance lets UK residents earn up to £1,000 per year from self-employment without needing to register with HMRC, file Self Assessment, or pay tax. Above £1,000, you can choose between deducting actual expenses or using the £1,000 Trading Allowance flat instead of expenses. Use whichever gives the better result. For low-cost service businesses (writing, tutoring, design), the Trading Allowance often saves both time and money.
You must register with HMRC by 5 October following the end of the tax year in which your self-employed income first exceeded £1,000. So if you started earning in May 2025 and earned over £1,000 in 2025/26, you must register by 5 October 2026. You can register online at gov.uk. Late registration triggers automatic penalties, so register as soon as you reasonably expect to exceed £1,000.
Payments on account are advance payments toward your next tax bill, required when your tax liability exceeds £1,000 per year. HMRC requires two payments, due 31 January and 31 July, each for half your previous year's tax. So if your 2024/25 tax was £6,000, you pay £3,000 in January 2026 and another £3,000 in July 2026, in addition to your actual 2024/25 tax bill. This catches most newly self-employed people off guard in their second year.
Yes, if you work from home. You can either claim HMRC's flat rate (£10 per month for 25 to 50 hours, £18 for 51 to 100 hours, £26 for 101+ hours per month worked from home) or deduct a proportion of actual home costs (council tax, energy, broadband, rent or mortgage interest) based on the percentage of your home used for business and the time used. The flat rate is simpler. The actual cost method is usually more generous for serious home-based businesses.
Making Tax Digital (MTD) for Income Tax requires self-employed people and landlords to keep digital records and submit quarterly updates to HMRC. From April 2026, MTD applies to anyone with self-employed or property income over £50,000. From April 2027, the threshold drops to £30,000. From April 2028, it drops to £20,000. If your turnover is approaching these thresholds, adopting MTD-compatible software like FreeAgent, QuickBooks, or Xero now is wise.