Side-Income Tax Estimator
Freelance work, selling online, a bit of consulting. This estimates what HMRC will want from it on top of your day job, and what you actually keep.
Your details
Gross, before tax. This decides which band your side income lands in.
Everything you were paid, before any costs.
Equipment, software, materials, travel for the work. If under £1,000, we use the trading allowance instead, which is better.
Updates as you change the figures. No submit button needed.
Result
£1,000
to set aside from £6,000 of side income. After expenses and tax you keep £4,500, an effective rate of 17%.
Where people get this wrong
The tax is not deducted as you go. It lands as one bill after 31 January following the tax year, and if it is over £1,000 HMRC also asks for half of next year's in advance at the same time, then the other half by 31 July. First-year side earners routinely get a bill 50% larger than the number here. Set aside £83 a month from day one and the January letter is a non-event.
How we calculate this
Profit is your side income minus either actual expenses or the £1,000 trading allowance, whichever is higher; you cannot use both. That profit is added on top of your salary and taxed at your marginal rate for 2026/27, using UK bands and the personal allowance taper above £100,000. We work out the tax on salary plus profit and subtract the tax on salary alone, so only the extra is shown.
Class 4 National Insurance applies to self-employed profits over £12,570 at 6%, then 2% above £50,270. It is calculated on your side profit alone, not combined with your salary, so most side hustles under that threshold pay none. Class 2 NI is no longer compulsory. This estimate assumes you are below State Pension age and does not apply the combined Class 1/Class 4 annual maximum, so NI may be overstated for someone also paying substantial employee NI. Pension relief, student loans and payments on account are not included. If you employ people, sell through a company, or earn rental income, the rules differ and this tool does not cover them.
This tool is for general guidance only and is not financial or tax advice. Always check your own circumstances, ideally with a qualified adviser or accountant, before making decisions.
Related reading
Income & Tax
What Your Tax Code Actually Means (And Why It's Probably Wrong)
HMRC issues millions of tax codes a year on estimates, not facts. If yours was never corrected after a job change, you've likely been overpaying without knowing it.
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The 60% Tax Rate Nobody Tells You About Between £100k and £125,140
There's no official 60% tax band in the UK, yet earners just over £100,000 pay it anyway. It's built from a personal allowance taper HMRC never advertises.