Consulting income does not behave like a salary, and HMRC does not treat it like one either. This guide covers the specific accounting tasks, tax obligations and structural decisions you need to understand as a UK-based consultant — whether you are just starting out or have been trading for a few years.

Why accounting for consultants is not the same as general small business advice

Most generic small business accounting content is built around product businesses with stock, employees and predictable monthly turnover. Consulting is different. Your income is project-based, often lumpy, and you may invoice a client once in January and not again until April. That pattern affects how you plan for tax, whether you need to register for VAT, and how you structure your business from day one.

Operating through a limited company adds another layer entirely. The off-payroll working rules (IR35) exist specifically to assess whether a consultant providing services through their own company should be taxed like an employee. Getting that wrong costs money. Getting it right requires understanding the rules on a contract-by-contract basis, not just once at the start.

Where most consultants go wrong with their accounting

The most common problems I see are not dramatic errors. They are quiet ones that build up over months — mixed personal and business finances, no provision set aside for Self Assessment, and a structure that made sense at the start but creates a tax problem two years later.

Not separating business and personal finances from day one

Running consulting income through a personal current account makes bookkeeping significantly harder. It also makes it difficult to claim expenses accurately and creates complications if HMRC asks questions. Open a dedicated business account as soon as you begin trading — this applies whether you are a sole trader or a limited company.

Ignoring IR35 because it feels complicated

Many consultants operating through a limited company either assume they are outside IR35 without checking, or assume they are inside it without understanding whether that is actually correct. IR35 is determined contract by contract, and the consequences of getting it wrong in either direction are real. If your client is a small private sector business, your own company makes the determination. If they are medium or large, they produce a Status Determination Statement.

What to do, in a clear order

There is no single right path for every consultant, but there is a sensible sequence that avoids the most common problems. Start with structure, then registration, then recording — and do not skip ahead.

1. Decide on your business structure before you take on your first contract. A sole trader setup is simpler and suits consultants with lower turnover and no IR35 exposure. A limited company offers potential tax advantages but brings Corporation Tax, annual accounts, and the possibility of IR35 applying. The expenses and reliefs available to each structure differ, so the choice affects your tax position from the start.
2. Register correctly with HMRC. Sole traders must register for Self Assessment. Limited company directors must register the company with Companies House and file Corporation Tax returns separately from their personal Self Assessment. If your turnover exceeds the VAT threshold (currently £90,000), you must also register for VAT. Check whether Flat Rate VAT suits your consulting business, as many service-based businesses benefit from it.
3. Set up a cloud accounting system and use it consistently from month one. QuickBooks, FreeAgent and Xero all handle invoicing, expense tracking and VAT returns well for consultants. The key is logging income and costs in real time rather than reconstructing twelve months of transactions in January. If you are registered for VAT, Making Tax Digital (MTD) rules mean you are already required to keep digital records and submit through compatible software.

For consultants operating through a limited company, add one more step: review each new contract against the IR35 tests before you sign. The HMRC CEST tool is a starting point, but its results are not binding and it does not capture every scenario. Speaking to an accountant before a new engagement begins is time well spent.

Costs and what to realistically expect

DIY bookkeeping using cloud software typically costs between £12 and £30 per month for a sole trader plan. A limited company with Corporation Tax, payroll and Self Assessment adds compliance obligations that most consultants find genuinely time-consuming to handle alone. Accountancy fees for a one-person limited company are commonly discussed in the range of £150 to £300 per month depending on the scope of work, with sole trader Self Assessment packages often sitting lower. The relevant question is not whether an accountant costs money — it is whether the time you spend on compliance is worth more than the fee, and whether you are at risk of filing errors that attract HMRC penalties.

How to get this sorted today

You do not need to overhaul everything at once. There are two actions that immediately reduce risk and give you a clearer picture of where you stand.

• Open a separate business bank account if you do not already have one, and begin logging all income and outgoings from today. Catching up on past months is easier than it sounds — cloud accounting software like QuickBooks or FreeAgent can import bank transactions and help you categorise them quickly.
• Check when your next HMRC deadline falls and confirm you are registered correctly. For sole traders, the Self Assessment deadline for online filing is 31 January following the tax year end. For limited company directors, Corporation Tax is due nine months and one day after your accounting period ends. If you are unsure which deadlines apply to you, a free introductory call takes less than twenty minutes and removes the guesswork.