Income from freelance work, selling goods or services, or any other self-employment activity is generally taxable. If you also have employment income, the two sources interact — your personal allowance and tax bands are shared — which affects both the marginal rate on your side income and how much you need to set aside.
Written and reviewed by James Whitfield · Updated August 2026 · Checked against 2026/27 HMRC rates · Editorial standards · Methodology
Side-hustle income becomes taxable once your gross self-employment income tops the £1,000 trading allowance. Above that you must register as a sole trader and file a Self Assessment return. If you are also employed, your salary uses up your £12,570 Personal Allowance and basic-rate band first, so side income stacks on top — which means a modest side hustle can be taxed at 40% even when the amount is small.
HMRC allows a £1,000 trading allowance each tax year.1 If your total gross income from self-employment (before any expenses) is £1,000 or less, you do not pay tax on it, do not need to register as self-employed, and do not need to file a Self Assessment return on the basis of that income alone.
If gross income exceeds £1,000, you must register as self-employed with HMRC, file a Self Assessment return and pay tax on any taxable profit above your overall tax-free amount. You cannot claim both the trading allowance and actual business expenses in the same calculation — you use whichever produces the better result.
For modest occasional income, the trading allowance provides a clean answer. Once income grows, Self Assessment obligations begin and need to be managed proactively.
If you have both PAYE employment income and self-employed side income, your tax position differs from someone purely self-employed. The Personal Allowance and basic rate band are shared across all sources: employment earnings are typically counted first, and self-employed profit sits on top.
This means that if your employment income already consumes your personal allowance and fills the basic rate band, your self-employed profit sits in the higher-rate band from the first pound — even if the side income itself is modest. Take a freelancer employed at £45,000 who earns an extra £10,000 from freelance work. Their salary uses the personal allowance and most of the basic-rate band, so only the slice of side income up to £50,270 is taxed at 20% and the rest at 40%. Class 4 NI does not enter into it here — that only bites once self-employed profit itself tops £12,570, and £10,000 is below that. The table below shows how it lands.
| Employment salary (fills allowance + basic band) | £45,000 |
| Side-hustle profit | £10,000 |
| Side income at 20% (£45,000 to £50,270 = £5,270) | £1,054.00 |
| Side income at 40% (£50,270 to £55,000 = £4,730) | £1,892.00 |
| Class 4 NI (profit below the £12,570 threshold) | £0.00 |
| Tax on the £10,000 side income | £2,946.00 |
Use the other income field in this calculator to enter your employed gross salary. The estimate will then calculate tax on your self-employed profit at the correct marginal rate. Without this, the calculator assumes all income starts from zero, which will understate your actual tax exposure.
Class 4 NI applies to self-employed profit above £12,570 regardless of whether the self-employment is full-time or a side income. At 6% on profits between £12,570 and £50,270, the Class 4 charge adds meaningfully to the effective rate on self-employed income.
If you are employed and earning above the NI primary threshold through PAYE, there is a maximum combined NI contribution limit. It is theoretically possible to have overpaid NI where employment and self-employment NI together exceed the annual maximum. HMRC handles this through Self Assessment but the interaction is not modelled in this calculator — check with HMRC or an accountant if this may apply.
If side income exceeds £1,000 gross in a tax year, register as self-employed with HMRC by 5 October following the end of that tax year. For income earned in 2026/27 (ending 5 April 2027), the registration deadline is 5 October 2027.
Once registered, you file a Self Assessment return covering both employment and self-employed income. PAYE employment income is pre-populated from employer data; you add your self-employed profit and expenses. Tax already paid through PAYE is taken into account and the return shows any remaining balance.
Keeping separate records of side-hustle income and expenses from the start — even a basic spreadsheet of invoices and costs — makes the return straightforward to complete and reduces the risk of missing allowable expenses.
If gross side income is £1,000 or less, the trading allowance applies and registration is not required. If it exceeds £1,000, you must register as self-employed and file a Self Assessment return.
Enter your gross employment salary in the other income field. The calculator will then estimate tax on your self-employed profit at the correct marginal rate, accounting for personal allowance and rate band already used by your employment income.
Class 4 NI at 6% applies to self-employed profit above £12,570. There is an annual maximum combined NI amount where employment and self-employment NI overlap — check with HMRC if this may apply to your situation.
Yes, if the costs are wholly and exclusively for the self-employed activity. The usual allowable expense rules apply. If your gross side income is only just above £1,000 and actual expenses are less than £1,000, using the trading allowance rather than actual expenses may be simpler.
More than you might think. Because the income stacks on top of your salary, the marginal rate is your real guide — 20%, 40% or even 60% between £100,000 and £125,140. If your salary already reaches into the higher-rate band, setting aside 40% of each side-hustle payment is a safe starting point; if you are firmly a basic-rate taxpayer, around 26% (20% tax plus 6% Class 4 NI, once profit tops £12,570) covers it. Enter your salary as other income in the calculator for the exact figure.
The rates, thresholds and rules in this guide are drawn from the official HMRC and GOV.UK sources below, using the confirmed 2026/27 figures. Each link opens the relevant official page in a new tab.
The sole trader tax calculator turns this guidance into a concrete monthly take-home and tax reserve estimate, based on 2026/27 HMRC rates. Enter taxable profit — not turnover.
Self Assessment checklist, expense tracker and payments on account calendar — all in one practical PDF. Updated for 2026/27.
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