Self-Employed Tax & NI Calculator (UK)

Self-Employment Tax Guide 2026/27

What's the key thing to understand about Self-Employed National Insurance?

Class 2 NI was abolished as a compulsory charge from April 2024 — self-employed people with profits above the Small Profits Threshold (£6,725) now get state pension qualifying years without paying it. Class 4 NI: 6% on profits between £12,570–£50,270 (cut from 9% in April 2024); 2% above £50,270. Unlike employee NI, there is no employer contribution for the self-employed, making the effective NI rate lower for the same gross income but providing fewer benefits coverage.

What do I need to know about Payment on Account?

Self-employed people pay income tax via self-assessment in two payments on account: 31 January (50% of prior year's bill, plus any balancing payment) and 31 July (50% of prior year's bill). In the first year of self-employment, no payments on account are due until January following the first tax year — this can create a large first-year bill. Budget 25–30% of profit monthly for tax and NI, or use a separate savings account to ring-fence tax funds as you earn.

What's the key thing to understand about Allowable Expenses?

Genuine business expenses reduce your taxable profit. Fully deductible: accountancy fees, business insurance, tools and equipment, professional subscriptions, travel to client sites (not commuting), marketing and website costs, software and subscriptions, office supplies. Partially deductible: home office (actual costs or HMRC's £6/week flat rate), phone and broadband (business proportion), car (actual costs or HMRC mileage rate of 45p/mile for first 10,000 miles), and capital equipment such as computers and tools (claimed via capital allowances rather than as a straightforward expense). Keeping accurate records of income and expenses throughout the year makes this calculation far easier — QuickBooks is built for exactly this, letting self-employed people track income, expenses and VAT from one place rather than reconstructing it all at tax return time.

What's the key thing to understand about Tax-Efficient Structures?

For profits regularly above £50,000–£60,000, incorporating as a limited company often becomes tax-efficient. As a director-shareholder, you can draw a small salary (to maintain NI record) and take dividends taxed at lower rates (10.75% basic rate). However, corporation tax on profits (25% above £50,000), additional accounting costs (£800–2,000/year), and loss of employment-related flexibility must be weighed. Seek accountant advice at this threshold — the breakeven varies with individual circumstances, profit level, and future plans for the business.

What's the key thing to understand about Allowable Business Expenses?

Self-employed tax is calculated on profit, not turnover — so every legitimate business expense deducted before tax reduces the tax bill. Common allowable expenses include office costs, business travel (but not ordinary commuting), stock and materials, staff costs, business insurance, professional subscriptions, and a proportion of home costs if you work from home, calculated either using HMRC's simplified flat rates based on hours worked from home, or a reasonable proportion of actual costs like heating, electricity, and internet. Capital items like equipment, tools, or a business vehicle are generally claimed through capital allowances rather than as a straightforward expense, which work slightly differently from day-to-day running costs. Keeping clear, dated records and receipts for every expense claimed is essential, since HMRC can request evidence, and expenses must be wholly and exclusively for business purposes — a meal with a client has different rules to simply covering your own lunch while working from home. Getting allowable expenses right is usually the single biggest lever a self-employed person has over their tax bill, more so than any allowance or relief applied afterward.

What should I know about Setting Aside Money for Your Tax Bill?

Because tax isn't deducted automatically from self-employed income the way PAYE deducts it from a salary, the biggest practical risk for newly self-employed people is simply not having the money put aside when the tax bill falls due. A common rule of thumb is to transfer a fixed percentage of every payment received — often somewhere between 20% and 30% depending on income level, since National Insurance is added on top of income tax — into a separate savings account the moment it's paid, so the money is never counted as 'available' to spend. It's also important to budget for 'payments on account': once a tax bill rises above a certain threshold, HMRC generally requires advance payments toward the following year's tax alongside the current year's bill, which can roughly double the amount due in the first year this applies and catches many newly self-employed people out. Setting money aside consistently, rather than trying to find it all at once near the filing deadline, is the most reliable way to avoid a stressful scramble or needing to borrow to cover a tax bill.

What should I know about Registering for Self Assessment?

If you're newly self-employed in the UK, you must register with HMRC for Self Assessment, generally by 5 October following the end of the tax year in which you started trading, to avoid a late-registration penalty. Once registered, you'll get a Unique Taxpayer Reference (UTR) and need to file a tax return each year even in years with little or no profit, since HMRC still expects a return until you formally tell them you've stopped trading. Many people underestimate how long registration and the first return can take, particularly around setting up a Government Gateway account and verifying identity, so starting early in the tax year rather than close to the January deadline reduces the risk of missing it. Keeping digital records of income and expenses from day one, rather than reconstructing them later, also makes the eventual return considerably faster and less error-prone, which matters given HMRC's ongoing move toward Making Tax Digital for the self-employed.

Worked Example: Full Tax and NI Bill on £45,000 Profit

Take a self-employed sole trader with £45,000 of taxable profit for the year, using the standard personal allowance of £12,570. Income tax: the first £12,570 is tax-free. The remaining £45,000 − £12,570 = £32,430 falls entirely within the basic rate band (up to £50,270), taxed at 20%: £32,430 × 0.20 = £6,486.00. Class 4 National Insurance: charged at 6% on profits between £12,570 and £50,270 (the rate was cut from 9% to 6% in April 2024). Since £45,000 is below the upper limit, the full £32,430 is taxed at 6%: £32,430 × 0.06 = £1,945.80. Total tax and NI due: £6,486.00 + £1,945.80 = £8,431.80, leaving take-home profit of £45,000 − £8,431.80 = £36,568.20 — an effective combined rate of about 18.7% on the full £45,000 of profit.

These rates and thresholds are those confirmed for recent tax years and are currently frozen under government policy rather than rising with inflation — always confirm the figures for the specific tax year on gov.uk before budgeting, since a frozen threshold combined with rising profits quietly pushes more income into higher bands over time (a effect often called 'fiscal drag').

How Trading Allowance Interacts With Small Side Income

The UK's trading allowance lets anyone with small amounts of self-employed or casual income — currently typically up to around £1,000 a year — earn that amount completely free of tax and without needing to register for Self Assessment at all, provided there's no other reason to file a return. Earn more than the allowance and the choice becomes whether to deduct the allowance itself or deduct actual business expenses, whichever is more favourable, rather than claiming both. This is particularly relevant for people with a side hustle alongside employed work, such as occasional freelance projects or selling items regularly rather than as a one-off clearout, where the income might otherwise fall through the cracks of standard PAYE reporting.

Class 2 NI: Why It Still Matters for Benefit Entitlement

Class 2 National Insurance for the self-employed has been reformed in recent years so that many with profits above the Lower Profits Threshold get NI credits automatically without actually paying Class 2 contributions, but those with profits below that threshold can still choose to pay voluntarily. Doing so matters because NI contributions and credits feed directly into eligibility for the State Pension and certain other contributory benefits, so someone with a low-profit year, perhaps in a business's early stages, may want to pay voluntary Class 2 contributions specifically to avoid a gap in their NI record, even though the amount involved is typically modest compared to the income tax and Class 4 NI calculated on larger profits.