Going freelance in the UK feels great — until January of your second year, when HMRC asks for what looks like 150% of last year’s tax bill in a single payment. This guide walks through exactly how UK sole trader tax works, so nothing about your Self Assessment is a surprise.
The good news: it’s simpler than it looks. There are only two taxes on your self-employed profits, and one clear cash-flow trap to plan for.
The two things you pay
As a sole trader, you’re taxed on your profits — that’s your revenue minus allowable business expenses. Not on the money that hits your bank account, and not on what you invoiced.
On those profits you pay:
-
Income Tax at the same bands as anyone else in the UK:
- 0% on the first £12,570 (personal allowance)
- 20% between £12,570 and £50,270
- 40% between £50,270 and £125,140
- 45% above £125,140
-
Class 4 National Insurance:
- 6% between £12,570 and £50,270
- 2% above £50,270
That’s it. Class 2 NI used to be a flat weekly amount, but from 2024/25 HMRC removed the actual charge — you still get state pension credit automatically once your profits pass £6,725.
Three worked examples
Let’s see what that means in practice. All examples assume no student loan and no other income.
£30,000 profit — small side business
- Income Tax: (£30,000 − £12,570) × 20% = £3,486
- Class 4 NI: (£30,000 − £12,570) × 6% = £1,046
- Total to HMRC: £4,532 — effective rate on profit: 15.1%
- Take-home: £25,468
£60,000 profit — mid-career freelancer
- Income Tax: (£50,270 − £12,570) × 20% + (£60,000 − £50,270) × 40% = £7,540 + £3,892 = £11,432
- Class 4 NI: (£50,270 − £12,570) × 6% + (£60,000 − £50,270) × 2% = £2,262 + £194.6 = £2,457
- Total to HMRC: £13,889 — effective rate on profit: 23.1%
- Take-home: £46,111
£120,000 profit — starting to feel the taper
At this level you enter the personal allowance taper zone (£100,000–£125,140), where every £2 of profit above £100k costs you £1 of personal allowance. That creates a 60% marginal rate.
- Personal allowance shrinks from £12,570 to £2,570 at £120k profit
- Income Tax works out to about £41,432
- Class 4 NI: £2,262 + (£120,000 − £50,270) × 2% = £2,262 + £1,395 = £3,657
- Total to HMRC: ~£45,089 — effective rate: 37.6%
- Take-home: ~£74,911
Notice how the effective rate jumps from 23% to 38% between £60k and £120k profit. Higher-rate territory + the taper is where sole trader tax really bites.
Use the self-employed tax calculator to plug in your own numbers.
The 30% rule (this will save your finances)
Every time an invoice lands in your bank account, immediately move a percentage of it into a separate savings account you don’t touch. Rough guidance:
| Annual profit range | Set aside per invoice |
|---|---|
| Up to £30k | 20% |
| £30k–£50k | 25% |
| £50k–£100k | 30% |
| £100k–£125k | 40% |
| £125k+ | 45% |
At the end of the tax year, the money is already there. You transfer it to HMRC and get on with your life. Freelancers who don’t do this end up borrowing to pay tax bills — a completely avoidable mess.
Payments on account — the January trap
Here’s the thing nobody warns you about your first year of Self Assessment.
If your tax bill is over £1,000, HMRC decides that next year’s bill will probably be similar, and asks you to prepay it in two instalments:
- 31 January: Pay last year’s balance in full, PLUS 50% of next year’s estimated bill.
- 31 July: Pay the other 50% of next year’s estimated bill.
So if you owe £14,000 for 2024/25, your January 2026 bill isn’t £14,000. It’s £14,000 + £7,000 = £21,000. Then another £7,000 in July.
It’s not extra tax — you’re just paying earlier than an employee does. But if you didn’t know it was coming, it can absolutely destroy your cash flow. The self-employed tax calculator shows this cash-flow schedule so you can plan for it in advance.
What counts as an allowable expense?
Anything you use wholly and exclusively for the business. The obvious ones:
- Software and SaaS subscriptions
- Hardware (laptop, monitor, phone if used mainly for work)
- Coworking desk or a portion of home-office costs
- Accountant fees
- Business insurance
- Travel to client sites (not commuting to a regular workplace)
- Professional development, courses, books
- Marketing and website costs
The tricky ones are things you use partly for work and partly personally — phone, home internet, car mileage. HMRC lets you claim a reasonable percentage, but keep records. If you’re new, an accountant costs £30–60/month and typically saves you more than that in the first year.
PAYE income on top?
If you also have a salaried job, your personal allowance is used up by that job first. Your self-employed profits then stack on top at your marginal rate — which could mean every pound of self-employed profit is taxed at 40% if your day job puts you into higher-rate territory.
In that case, an even higher setting-aside percentage applies. Use the UK take-home calculator to see what your PAYE side already claims, then treat freelance profits as taxed at 40%+ from the first pound.
When to think about a limited company
Rough rule of thumb: once your profit is comfortably above £50,000 and you don’t need all of it as income, running through a limited company can be more tax-efficient — because Corporation Tax + dividend tax often beats Income Tax + NI at higher levels. It also adds complexity (accounts, filings, IR35 if you contract), so this isn’t a decision to rush. Talk to an accountant when you cross that threshold.
Related calculators
- Self-employed tax calculator — the tool this article walks through.
- Freelance hourly rate calculator — set the right rate before you invoice.
- UK take-home pay (PAYE) — compare with the equivalent salaried job.
- VAT calculator — once you cross £90k turnover you’ll need this.
- Break-even calculator — for freelancers with hardware or software costs.
Freelance tax feels intimidating on paper. In reality it’s two calculations, one savings account, and a January reminder in your calendar. Get those three right and Self Assessment becomes an admin task, not a source of dread.