Understanding your tax obligations as a self-employed person in the UK is not optional. HMRC expects you to calculate what you owe, register yourself, and pay on time. If you do not, you face penalties, interest, and potentially an investigation.
The system is not as complicated as many people assume, but it does require you to know the rules. This guide covers income tax bands, National Insurance contributions, the payment on account system that catches so many people out, allowable expenses, and the deadlines that matter.
Use the Self-Employed Tax Calculator to work out your specific tax position once you have read through the framework below.
Who Needs to Register as Self-Employed
You need to register for Self Assessment and notify HMRC that you are self-employed if your self-employed income exceeds £1,000 in a tax year (the trading allowance). Even if you are already employed and pay PAYE, any freelance or self-employed income above £1,000 needs to be reported.
Register with HMRC as soon as you start trading, and no later than 5 October following the end of the tax year in which you started. Missing this deadline can result in penalties.
The UK tax year runs from 6 April to 5 April the following year.
Income Tax: The Bands for 2024/25
Income tax is charged on your profits, not your turnover. Profits are your income from self-employment minus your allowable business expenses.
The income tax bands for 2024/25 (England, Wales, and Northern Ireland) are:
Personal Allowance: £12,570. You pay no income tax on this amount. If your total income (including employment income) exceeds £100,000, the personal allowance is gradually withdrawn at a rate of £1 for every £2 over £100,000. It disappears entirely at £125,140.
Basic Rate: 20% on taxable income between £12,571 and £50,270.
Higher Rate: 40% on taxable income between £50,271 and £125,140.
Additional Rate: 45% on taxable income above £125,140.
These are cumulative bands. If your taxable income is £60,000, you pay 20% on the portion between £12,571 and £50,270, and 40% on the portion between £50,271 and £60,000.
Scotland has different income tax rates and bands. If you live in Scotland, the Scottish rates apply to your non-savings, non-dividend income.
National Insurance for the Self-Employed
Self-employed people pay National Insurance differently from employees. You are responsible for two classes.
Class 2 National Insurance. This was historically a flat weekly rate, but from April 2024, HMRC changed how it works. Class 2 NI is now only payable if your profits are above the Small Profits Threshold (£12,570 for 2024/25). Below that threshold, you are not required to pay, but you can make voluntary contributions to protect your entitlement to state pension and other contributory benefits.
If your profits are above £12,570, Class 2 NI is included in your Self Assessment calculation.
Class 4 National Insurance. This is income-related, calculated as a percentage of your self-employed profits.
- 6% on profits between £12,570 and £50,270
- 2% on profits above £50,270
Note: the Class 4 main rate was reduced from 9% to 6% from 6 April 2024. If you are reading guides from before that date, those rates are no longer current.
Class 4 NI is calculated and paid through your Self Assessment return alongside income tax.
Payment on Account: The System That Catches People Out
Payment on account is the mechanism HMRC uses to collect your tax in advance. It is one of the most common sources of financial stress for newly self-employed people because it is not widely understood until the first large bill arrives.
Here is how it works.
When you file your first Self Assessment return, you pay the tax you owe for that year (your "balancing payment"). If your tax bill is over £1,000 and less than 80% was collected through PAYE, HMRC also asks you to make two advance payments toward the following year's bill.
Each advance payment is 50% of your current year's tax bill, due on:
- 31 January (alongside your balancing payment for the previous year)
- 31 July
This means that in your first year of Self Assessment, you might pay your actual tax plus 100% of it again in advance, all in the same tax year. That can mean paying effectively 18 months of tax in a single year.
An example. You file your return for 2023/24 on 31 January 2025 and discover you owe £5,000 in income tax and NI. Because this is above £1,000, HMRC also requires you to make a payment on account toward 2024/25. You pay £5,000 (the balancing payment) plus £2,500 (the first payment on account). Total due on 31 January 2025: £7,500. Then on 31 July 2025, you pay another £2,500.
You have paid £10,000 toward a £5,000 tax year because the system requires advance payments. The excess will be credited against your next bill or refunded.
The lesson is to set aside money for tax from the moment you start earning. Many accountants recommend putting aside 25-30% of every payment you receive. The exact percentage depends on your profit level and tax band.
Key Deadlines
Missing HMRC deadlines results in automatic penalties. The key dates for Self Assessment are:
5 October. Deadline to register for Self Assessment if you are filing for the first time for the previous tax year.
31 October. Deadline for submitting paper Self Assessment returns (most people now file online).
31 January. Deadline for filing online returns, and the payment deadline for any balancing payment plus the first payment on account for the following year.
31 July. Deadline for the second payment on account.
Late filing: £100 penalty immediately, increasing to £10 per day after 3 months (up to a maximum of £900), then further penalties at 6 and 12 months.
Late payment: 5% surcharge on unpaid tax after 30 days, additional 5% after 6 months, and another 5% after 12 months. Interest also accrues on unpaid amounts.
Allowable Expenses: What You Can Deduct
Allowable expenses reduce your taxable profit, so understanding what qualifies is directly worth money to you.
Office costs. If you work from a dedicated home office, you can claim a proportion of household costs (heating, electricity, internet, insurance) based on the number of rooms used for business and the proportion of time. Alternatively, HMRC's simplified flat rate is £10 per month for up to 25 hours worked at home per month, £18 for 25-50 hours, and £26 for 51 hours or more.
Equipment. Computers, monitors, cameras, tools, and other equipment used for work. Under the Annual Investment Allowance (AIA), you can deduct the full cost in the year of purchase rather than spreading it over the asset's life.
Travel. Business travel (not commuting) is allowable. Mileage for business journeys in your own vehicle can be claimed at HMRC's approved rates: 45p per mile for the first 10,000 miles, 25p per mile above that.
Professional subscriptions and memberships. Industry association fees, professional registrations, and relevant trade publications.
Marketing and advertising. Website hosting, design, advertising spend, business cards, and similar costs.
Training. Courses, books, and resources that are directly relevant to your existing business activity. Note: training to start a new, different business is not allowable.
Software and subscriptions. Tools you use for your business, including accounting software, project management tools, communication platforms, and specialist software.
Bank charges and professional fees. Business bank account charges, accountant fees, legal advice related to your business.
Phone. The business-use proportion of your phone bill. If your phone is used 60% for business, you can claim 60% of the cost.
Clothing. Protective equipment and uniforms required for work. General smart clothes you wear to meet clients do not qualify (HMRC's position is that these can be worn outside of work).
Keep receipts for everything. Digital records are fine. Many accounting apps let you photograph receipts and link them to transactions automatically.
What Triggers an HMRC Investigation
HMRC selects returns for investigation using a combination of risk scoring, random selection, and specific triggers. While you cannot entirely eliminate the risk, understanding what attracts attention helps you keep your records clean.
Inconsistency with previous years. A sudden large drop in income or a sudden spike in expenses compared to prior years will be noticed.
Industry benchmarks. HMRC has data on typical profit margins and expense ratios by industry. If your figures are outliers, that can trigger a check.
High expenses as a proportion of income. If your expenses consistently run at 80-90% of income and your profit is very low, particularly for a personal service business, that raises questions.
Inconsistency between VAT returns and income tax. If your VAT returns show different turnover figures to your Self Assessment return, HMRC will notice.
Missing income. If you receive payments that HMRC can identify (via bank data, third-party reporting, or IR35 investigations at clients), but your return does not reflect that income, you will be asked to explain the discrepancy.
The best protection against investigation is accurate, consistent records and a return that reflects the genuine reality of your business. If your expenses are legitimately high, document why. If your income dropped, be able to explain it.
Getting the Numbers Right
Self-employed tax is not something to estimate or guess. Use the Self-Employed Tax Calculator to get an accurate figure based on your actual profits, and set aside the corresponding amount each month.
Consider working with an accountant, particularly in your first year of self-employment. A good accountant will save you more than their fee through proper expense claims and help you avoid the mistakes that lead to investigations. They will also take the administrative pressure off so you can focus on running your business.
The VAT Calculator is also useful if you are approaching the VAT registration threshold, and the Invoice Generator ensures your invoices are correctly formatted for both your clients and HMRC's requirements.