If you are contracting in IT and handling your own accounts, there is a good chance IR35, corporation tax, and self assessment are sitting in a mental pile marked ‘deal with later.’ This guide explains exactly what you need to manage, what the risks are if you ignore it, and what a proper setup looks like in practice.

Why accounting for IT contractors carries specific risks

IT contracting sits at a complicated intersection of employment law, tax legislation, and business structure decisions that most generic accounting advice does not cover. Whether you operate through a personal service company (PSC), a limited company, or as a sole trader, each structure carries its own compliance obligations and tax treatment. Getting this wrong costs real money, and HMRC does audit contractors.

The off-payroll working rules (IR35) are the most significant piece of legislation affecting IT contractors in the UK. They exist to ensure that a contractor who would effectively be an employee if hired directly pays broadly the same Income Tax and National Insurance as an employee would. If your contract is caught by these rules and you have not accounted for it, the liability is yours.

Where most IT contractors go wrong

The majority of problems I see with IT contractor accounts are not caused by deliberate non-compliance. They are caused by contractors assuming the rules that applied when they started still apply now, or by copying what a friend does without checking whether their situation is actually the same. The three areas below account for the majority of the issues.

Misunderstanding their IR35 status

IR35 status is not fixed. It can change with each new contract or client, and the rules differ depending on whether your client is a small business or a mid-to-large business. For mid and large clients, the client is responsible for making the status determination. For small clients, the responsibility sits with you. Many contractors assume they are outside IR35 without ever formally checking, which is a significant risk. HMRC’s Check Employment Status for Tax (CEST) tool is the official way to assess your status, and HMRC will stand by results produced by it as long as the information you provide is accurate.

Taking dividends without planning for corporation tax

IT contractors operating through a limited company often pay themselves a combination of salary and dividends to manage their tax position. The problem arises when dividends are taken without reserving enough for the corporation tax bill. The current Corporation Tax rate is 25% on profits above £250,000, with a reduced small profits rate of 19% on profits up to £50,000. If your company profits sit between those thresholds, Marginal Relief may apply. Taking money out before calculating what you actually owe is one of the most common and fixable mistakes.

What to do, step by step

If you are setting up your accounting properly for the first time, or catching up after a period of doing the minimum, the steps below are the order in which to work through it. Each one has a direct link to a specific compliance obligation.

1. Determine your IR35 status for every active contract. Use the CEST tool at GOV.UK for each engagement separately. Save the result as it can serve as a valid status determination statement. Do this before you consider any other accounting decisions, because your IR35 status determines how you pay tax.
2. Choose and set up the right business structure. If you are outside IR35 and billing regularly, a limited company usually offers a more tax-efficient structure than a sole trader arrangement or an umbrella company. Each option has different administrative responsibilities. GOV.UK explains how umbrella companies work and what your employment rights are under that model.
3. Set up compliant bookkeeping from the first invoice. Record every payment received, every allowable expense claimed (equipment, training, home office, software licences), and keep a running reserve for your VAT liability (if registered) and corporation tax. Waiting until year-end to reconcile twelve months of records costs far more in accountancy fees and creates gaps that HMRC notices.

Once those three foundations are in place, year-end accounts, corporation tax returns, and self assessment all follow a predictable process. The chaos that most contractors experience comes from skipping steps one and two and then trying to work backwards.

Costs and what to expect

The cost of getting your IT contractor accounting wrong is not just the accountancy fees to fix it. HMRC can issue penalties for late or inaccurate returns, and an IR35 investigation can result in significant back-tax demands plus interest. At STZ Accounting, limited company packages start from £215 per month for turnover up to £100,000, covering bookkeeping, limited company accounts, corporation tax, VAT returns, payroll, self assessment for directors, and monthly management reports. That is a fixed price with no tie-in. The table below compares the main approaches IT contractors take.

How to get started today

You do not need to have everything in order before speaking to an accountant. In fact, the earlier you have the conversation, the cheaper and simpler it is to put things right. If you are an IT contractor currently operating without proper accounting support, or if you are unsure whether your current setup is compliant, the two actions below are the practical starting points.

• Run your current contract through HMRC’s CEST tool at GOV.UK and save the result. This takes around ten minutes and gives you a clear picture of your IR35 position before any other decision is made.
• Book a free call with David at STZ Accounting. Bring your current setup, your business structure, and any questions about what you owe or may have missed. Same-day responses are standard and there is no obligation after the call.