If you are self-employed — whether full-time freelance, running a side hustle alongside a PAYE job, or contracting through your own business — you are responsible for calculating and paying your own income tax and National Insurance. Unlike employees who have deductions handled automatically through PAYE, self-employed workers must register with HMRC, keep records, file a Self-Assessment tax return, and pay their bill in scheduled instalments. This guide covers the complete picture for the 2026/27 tax year: how to register, what you can deduct, the Class 2 and Class 4 NI charges, and how to estimate your total bill.[1]
When do I need to register for Self-Assessment?
You must register with HMRC as self-employed if your self-employed income exceeds the £1,000 Trading Allowance in a tax year. The registration deadline is 5 October following the end of the tax year in which you started trading. For example, if you started freelancing in June 2026, you must register by 5 October 2027. Registration is done online through HMRC's website, and once registered you will receive a Unique Taxpayer Reference (UTR) and be enrolled for Self-Assessment.
If you miss the registration deadline, HMRC may charge penalties — even if you do not owe any tax. The penalty regime starts at £100 for being one day late with your return and escalates from there. It is always better to register on time and file a nil return if your profits turn out to be below the threshold. Registration does not mean you will automatically owe tax; it simply means you are in the system.
You do not need to register if your total self-employed income (before expenses) is under £1,000. The Trading Allowance covers this amount automatically without any paperwork. If you earn between £1,000 and your Personal Allowance of £12,579 from self-employment alone, you will need to register and file, but your actual tax bill will be nil or very small.
How is self-employed income tax calculated?
Self-employed income tax works exactly the same way as employed income tax. Your taxable profit (total income minus allowable expenses) is added to any other income you have, and the combined total is taxed using the standard income tax bands for 2026/27:
- Personal Allowance: £0–£12,579 at 0%
- Basic Rate: £12,579–£50,270 at 20%
- Higher Rate: £50,270–£125,140 at 40%
- Additional Rate: over £125,140 at 45%
If you also have employed income (a day job), your self-employed profits are added on top of your salary. This means if your salary already uses up your Personal Allowance and most of the Basic Rate band, your self-employed profits may be taxed entirely at 40%. The two income streams are combined for the purposes of determining your tax band — there is no separate allowance for self-employed income.
For example, on a self-employed profit of £40,000 with no other income, your income tax bill would be approximately £5,484 — that is 20% on everything between £12,579 and your profit level. Use our freelancer tax calculator to get a precise figure including Class 4 NI.
What is Class 4 National Insurance?
Class 4 NI is the main National Insurance charge for self-employed people. It is calculated as a percentage of your annual taxable profits and collected through Self-Assessment (not monthly like employee NI). For 2026/27, the rates are:
- 6% on profits between £12,570 and £50,270
- 2% on profits above £50,270
The 6% main rate is notably lower than the 8% rate that employed workers pay. This is one area where self-employment has a genuine tax advantage — though it comes with the trade-off that employers also pay NI on behalf of employed staff (contributing to workplace pensions and other benefits). On a profit of £40,000, your Class 4 NI bill would be approximately £1,646 for the year.
What is Class 2 National Insurance?
Class 2 NI is a flat-rate weekly contribution of £3.45/week for 2026/27. You only pay Class 2 if your profits exceed the Small Profits Threshold of £6,725 per year. Class 2 contributions count towards your State Pension entitlement and eligibility for certain contributory benefits (Maternity Allowance, Bereavement Support Payment). The annual cost is modest — approximately £179 per year — and it ensures you build qualifying years for your State Pension.
If your profits are below £6,725, you are not required to pay Class 2, but you can choose to pay voluntarily to maintain your NI record. This is usually worthwhile because the cost is very low relative to the State Pension benefit it secures. Each qualifying year adds approximately £6.30/week to your eventual State Pension — a return that far exceeds the Class 2 contribution.
What expenses can I deduct?
You can deduct legitimate business expenses from your income before calculating tax. The key test is that the expense must be “wholly and exclusively” for business purposes. HMRC accepts a wide range of deductions for self-employed people:
- Office costs — stationery, phone bills, internet, software subscriptions, computer equipment
- Travel — business miles at 45p/mile for the first 10,000 then 25p thereafter, public transport, parking for business meetings
- Working from home — simplified expenses at £6/week (no receipts needed) or a proportion of actual household costs (electricity, heating, council tax)
- Professional services — accountant fees, professional insurance, legal costs relating to your business
- Marketing — website hosting, advertising, business cards, portfolio costs
- Training — courses, books, and conferences directly related to your current trade (not training to enter a new trade)
- Equipment — capital allowances for larger purchases like a laptop, camera, or specialist tools
You cannot claim for clothing (unless it is a specialist uniform or protective gear), food (unless you are away overnight for work and cannot reasonably eat at home), fines or penalties, client entertainment, or personal expenses mixed with business use unless you correctly apportion the business percentage. Keep all receipts and records for at least five years — HMRC can open an enquiry into any return within that window.
How do payments on account work?
If your Self-Assessment tax bill exceeds £1,000 (after deducting tax already collected through PAYE, if any), HMRC requires “payments on account” — advance payments towards next year's bill. Each payment is 50% of the previous year's Self-Assessment liability, due on 31 January and 31 July. A balancing payment is made the following 31 January once your actual bill is known.
This system can be a significant cash flow shock in your first profitable year. Imagine your year-one bill is £5,000. On 31 January, you pay that £5,000 plus the first payment on account of £2,500 for year two — a total of £7,500 in one hit. Then on 31 July you pay another £2,500. Budget for this by setting aside 25-30% of your profits throughout the year into a separate savings account. See our payments on account guide for strategies to manage this.
You can apply to reduce payments on account if you expect next year's bill to be lower (for example, if income is dropping). However, if you reduce them too much and your actual bill turns out to be higher, HMRC will charge interest on the underpayment. Only reduce if you are confident your income is genuinely falling.
What are the key Self-Assessment deadlines?
| Deadline | What |
|---|---|
| 5 October | Register as self-employed (if new — by 5 Oct following end of first tax year) |
| 31 October | Paper tax return deadline (rare — most file online) |
| 31 January | Online tax return deadline + pay balance + first payment on account for next year |
| 31 July | Second payment on account for current year |
Missing the 31 January online deadline triggers an immediate £100 penalty, followed by daily penalties after three months, and tax-geared penalties after six and twelve months. Missing the payment deadline incurs interest (currently around 7.5% per annum) from day one, with additional surcharges if you are still unpaid after 30 days and six months.
How do I estimate my self-employed tax bill?
Use our freelancer tax calculator to estimate your total tax bill. Enter your net profit (income minus allowable expenses) and the calculator will show your income tax, Class 4 NI, and total deductions. If you also have PAYE income, the calculator handles the interaction between the two income streams — showing how your self-employed profits are taxed on top of your salary.
For a quick estimate on a profit of £40,000, your approximate total bill would be income tax of £5,484 plus Class 4 NI of £1,646 plus Class 2 of approximately £179 — a total of around £7,309. This assumes no other income and no pension deductions. The freelancer calculator gives the exact figure after accounting for all variables.
Sources
- HMRC — Self-employed National Insurance rates. Accessed July 2026.
- HMRC — Register for Self-Assessment. Accessed July 2026.