Side Hustle Tax for Tradespeople — Declaring Foreigners and Weekend Work (2026)

The "cash is invisible" myth

Let's deal with the big one first. The idea that cash jobs leave no trail belongs to a different era. HMRC no longer relies on someone grassing you up or an inspector knocking on the door. It runs a vast data-matching system and pulls information from banks, online platforms and your customers' own tax returns. We'll come to exactly how that works later — but the short version is that "they'll never find out" is the single most expensive assumption in the trade. It's not a question of whether HMRC can see undeclared income; it's a question of when the data flags it.

The good news is that declaring side work is far simpler and cheaper than most people fear. For a lot of tradespeople it costs nothing at all, thanks to a specific allowance designed for exactly this situation.

The £1,000 trading allowance — your free pass

Since 2017 there has been a £1,000 trading allowance. In plain terms: you can earn up to £1,000 gross from self-employment or casual trading in a single tax year (6 April to 5 April) without having to declare it or pay any tax on it. You don't need to register for Self Assessment, you don't need to tell HMRC, and you don't need to keep formal accounts. If your total side income from foreigners across the whole year is £1,000 or less, you're done.

The number is gross — it's the total money in, before you take off materials or fuel. So if you did three small jobs for £400, £300 and £250, that's £950 gross and you're under the line. Do one more £200 job and you're at £1,150 — over the threshold, and now the rules change.

Once you go over £1,000 gross, you must register for Self Assessment and declare the income. At that point you get a choice. You can either deduct the £1,000 trading allowance as a flat figure and pay tax on the rest, or deduct your actual allowable expenses — whichever leaves you better off. If you spent very little on materials, take the £1,000 allowance. If you spent more than £1,000 on materials, tools and mileage, claim the real expenses instead. You can't do both, and you pick the better option each year.

If you've got a PAYE job AND side work

This is the situation most employed tradespeople are in, and it confuses people because it feels like you can only be one thing — employed or self-employed. You can be both at the same time. You keep your PAYE job exactly as it is; your employer carries on deducting tax and National Insurance through payroll. Separately, you also register as self-employed for the side work and file a Self Assessment tax return once a year.

The tax return is where the two halves of your income meet. You report your PAYE earnings (the figures are on your P60) and your self-employed profit from the foreigners, and HMRC works out the combined picture. You don't pay tax twice — the return simply makes sure the right total tax is paid across everything you earned.

To register, you tell HMRC you've started getting self-employed income. The deadline is 5 October following the end of the tax year in which you crossed the threshold. So if you went over £1,000 in the 2025/26 tax year, you needed to register by 5 October 2026, with the return itself due by 31 January 2027 if you file online.

You're taxed on profit, not turnover

A common worry is "I can't afford to pay tax on the whole £3,000 I took in cash." You don't. Tax is charged on your profit — the money left after you deduct legitimate business expenses. For a tradesperson doing side work, allowable expenses typically include:

• Materials and consumables bought specifically for the job
• Tools and equipment used for the work
• Mileage to and from jobs (currently 45p per mile for the first 10,000 business miles)
• A share of your phone bill, work clothing/PPE and any trade-specific insurance
• Disposal and waste-carrier costs, hire charges and small subcontract payments

So if you took £3,000 in side income and spent £1,200 on materials, fuel and a few tools, your taxable profit is £1,800 — not £3,000. Keeping a clean record of every job and every receipt is what makes this work in your favour, because every legitimate expense you can evidence reduces the profit you pay tax on. Logging side jobs and their costs in something like Trade2Base as you go means the figure you put on your return is the real one, not a guess you cobble together in January.

Why side-hustle profit is usually taxed at 20% (or 40%)

Here's the bit that catches employed tradespeople out. Everyone gets a tax-free personal allowance (£12,570 for 2025/26). But if you have a full-time PAYE job, that allowance is almost always used up entirely against your wages. That means your side-hustle profit doesn't get its own slice of tax-free income — it sits on top of your salary and is taxed from the first pound.

For most employed tradespeople that means side profit is taxed at the basic rate of 20%. If your wage plus side profit pushes your total income over the higher-rate threshold (£50,270), the portion above that line is taxed at 40%. On top of income tax you'll usually pay Class 4 National Insurance on self-employed profits above the threshold as well. None of this is a reason to panic — it just means you should set money aside as you go rather than being hit with a bill you haven't budgeted for.

A safe rule of thumb: put roughly 30% of every side-job profit into a separate savings pot. For most people that comfortably covers the 20% income tax plus Class 4 NIC, with a little spare. Higher-rate earners should set aside more.

How HMRC actually finds out

This is where the "cash is invisible" myth falls apart completely. HMRC has multiple, overlapping ways of spotting undeclared trade income:

• Connect — the data-matching system. HMRC's Connect platform cross-references dozens of data sources — bank accounts, Land Registry, DVLA, council records, credit reference agencies and more — looking for patterns that don't add up. It flags people whose financial footprint doesn't match their declared income.
• Bank data. Regular cash deposits or transfers from customers that don't correspond to any declared income are a classic trigger. "Cash" rarely stays as cash — it ends up in an account.
• Digital-platform reporting. Since the rules came into force, online marketplaces and platforms now report seller and provider income directly to HMRC. If you pick up jobs through apps, marketplaces or platforms, that income is reported whether you declare it or not.
• Your customers' tax returns. If a landlord or business pays you to do work and then claims that cost against their own tax, your name and the amount appear in their records. A repair claimed by them with no corresponding income declared by you is an obvious mismatch.
• Lifestyle and tip-offs. A declared income that can't plausibly support a new van, a holiday or a mortgage raises questions. HMRC also runs a tax evasion reporting line, and disgruntled customers, ex-partners and even competitors use it.

You don't need to trip all of these — one solid mismatch is enough to open an enquiry, after which they'll go looking for the rest.

The real risks of not declaring

When HMRC catches undeclared income, the bill is never just the tax you originally owed. It typically stacks up as:

• Back tax — the income tax and NIC you should have paid, potentially going back several years (up to 20 years where the failure is deliberate).
• Interest — charged on the unpaid tax for every day it was late, which adds up significantly over multiple years.
• Penalties — a percentage of the unpaid tax. Penalties are far lower if the error was careless and you came forward, and far higher (up to 100% of the tax, sometimes more) where HMRC decides the non-declaration was deliberate and concealed.
• Prosecution — reserved for serious, deliberate cases, but tax fraud is a criminal offence and HMRC does prosecute. A criminal record is a poor trade-off for a few cash jobs.

A full tax investigation is also stressful and time-consuming — HMRC can demand years of bank statements and records and will keep digging until the figures reconcile. The cost in worry and accountant's fees alone usually dwarfs whatever tax was avoided in the first place.

How to put it right if you've already done cash work

If you've been doing foreigners and haven't declared them, the worst thing you can do is wait to be caught. Coming forward voluntarily almost always results in far lower penalties than being found by HMRC, and it takes the threat of prosecution off the table in all but the most serious cases.

HMRC runs a Digital Disclosure Service for exactly this. You notify them that you have undeclared income, then you have a window to work out what you owe across the relevant years and pay it. It's a structured, well-trodden process — thousands of tradespeople have used it to get straight. If the figures are large or span many years, get an accountant to handle the disclosure; the fee is money well spent and they'll often negotiate the penalty down.

Practical steps to stay clean

• Record every job. Date, customer, what you did, what you charged and what it cost you. A simple running log is all HMRC asks for — keep receipts for materials, tools and fuel.
• Watch the £1,000 line. Total your gross side income across the tax year. The moment it's heading over £1,000, plan to register.
• Register on time. By 5 October following the tax year you crossed the threshold. Late registration is itself a penalty trigger.
• Put money aside. Roughly 30% of each job's profit into a separate pot so the January bill is already covered.
• Keep it together. Logging side jobs in Trade2Base as you do them means your return is built from real records, not a frantic shoebox reconstruction.

Quick reference: side income and what you must do

The bottom line

Foreigners and weekend work are a normal, legitimate way for tradespeople to earn extra — there's nothing wrong with the work itself. What gets people into trouble is treating cash as invisible and skipping the simple admin. Stay under £1,000 and you owe nothing and do nothing. Go over it, register, keep clean records, claim your expenses and set money aside, and the whole thing is a minor once-a-year task rather than a risk hanging over you. The data has caught up with cash — declaring properly is now the cheapest and least stressful option by a distance.