From April 2029, individuals who earn employment income and also generate additional income from self-employed activities – commonly referred to as “side hustles” – will be required to pay the tax on those additional earnings through their PAYE tax code. Crucially, this will apply regardless of whether the income has actually been received at the time the tax is deducted.

At first glance, this may appear to be a minor administrative adjustment designed to simplify tax collection. In reality, it represents a significant and potentially damaging shift in the way tax is assessed and collected, with serious implications for cash flow and fairness.

Side-hustle income is, by its nature, unpredictable. Many individuals take on occasional freelance work, consultancy projects, or small trading activities alongside their main employment. Income levels fluctuate, contracts fall through, clients delay payment, and in some cases expected income never materialises at all. Under the proposed rules, HMRC will estimate what it believes an individual will earn and adjust their PAYE code accordingly, reducing take-home pay based on assumptions rather than confirmed results.

This creates a real risk that taxpayers will be taxed on income they have not yet earned, or may never earn. While overpayments may eventually be refunded, experience shows that HMRC errors are not uncommon, and correcting them can be slow and frustrating. Refunds often take months, during which time the taxpayer bears the cost of the cash-flow shortfall.

The reform also raises broader concerns about accuracy and accountability. PAYE coding is already prone to error, even in relatively straightforward cases. Introducing estimated self-employed income into the system increases complexity substantially and places a heavy reliance on HMRC’s ability to forecast future earnings accurately. For many taxpayers, that confidence is unlikely to be well placed.

There is also a wider economic concern. Side hustles are not typically undertaken to avoid tax; they are a response to rising living costs, job insecurity, or a desire to build something independently. For many, they represent an entry point into entrepreneurship or a way to test a business idea before committing fully. A system that taxes projected income in advance risks discouraging this activity and penalising those who are trying to improve their financial resilience.

While the detailed rules have yet to be finalised, the direction of travel is clear: the tax system is becoming more aggressive, more assumption-based, and less tolerant of irregular income patterns. Waiting for HMRC to correct matters after the event is rarely an effective strategy.

Against that backdrop, proactive tax planning has never been more important. Taking time to review existing tax arrangements can often produce immediate and legitimate savings. This is particularly relevant for higher earners, many of whom are unaware that they may be falling into the effective 60 per cent tax band caused by the withdrawal of the personal allowance between £100,000 and £125,140.

With careful and entirely lawful planning, it is possible in many cases to earn well into six figures while significantly reducing exposure to higher and additional rates of tax. The key is acting early, before PAYE codes, estimated assessments, and rigid collection mechanisms begin to dictate outcomes.

The underlying message is clear. The tax landscape is shifting towards earlier collection, heavier reliance on estimates, and reduced flexibility for taxpayers. Those who plan ahead and take control of their position will be far better placed than those who leave matters to automatic systems and retrospective corrections.