IR35 Inside Outside UK

Overview

Calculate IR35 Inside Outside UK using the official rates and regulations for United Kingdom.

How it works

Enter the base amount and the calculator will apply the relevant rates and brackets to compute the result.

Understanding IR35 and Off-Payroll Working Rules

IR35, formally known as the off-payroll working rules, is legislation designed to prevent tax avoidance by workers who supply their services through an intermediary, typically a personal service company, but who would be classified as employees if engaged directly. The rules ensure that such workers pay broadly the same income tax and National Insurance as employees in similar circumstances. Since April 2021, responsibility for determining IR35 status for contractors working with medium and large private sector clients rests with the end client, not the contractor. The end client must issue a Status Determination Statement (SDS) explaining whether the engagement falls inside or outside IR35, and the fee payer must deduct tax and NI through the deemed payment calculation if inside. For small companies, defined by Companies Act thresholds, the contractor remains responsible for determining their own status. Public sector engagements have been subject to these rules since April 2017. The determination considers multiple factors including personal service, mutuality of obligation, control, financial risk, provision of equipment, right of substitution, and whether the contractor is in business on their own account. No single factor is decisive, and the overall picture must reflect the genuine nature of the working relationship.

Inside vs Outside IR35: What It Means for Take-Home Pay

The financial impact of an inside IR35 determination is substantial, as the deemed payment calculation effectively treats the contractor as an employee for tax purposes. A contractor earning £500 per day inside IR35 through their limited company would see approximately 25-30% of their income absorbed by income tax, National Insurance (both employee and employer elements), and the apprenticeship levy, compared to approximately 15-20% outside IR35 with the optimal salary and dividend split. Over a 200-day contract, this difference can amount to £15,000-20,000 in additional tax. Contractors determined as inside IR35 often find that switching to an umbrella company simplifies compliance while delivering similar net income to operating through a limited company subject to deemed payment, as the umbrella handles all PAYE deductions and employment administration. The key decision point is whether the working practices genuinely reflect self-employment, and contractors should not simply accept an inside determination without reviewing the detailed reasoning in the SDS and exercising their right to dispute it through the client's disagreement process.

Challenging an IR35 Determination

Contractors who receive an inside IR35 determination have the right to dispute it through the client's status disagreement process. The client must respond within 45 days, providing reasons for their decision. If the dispute is unsuccessful, the contractor can escalate to HMRC, though this carries the risk of triggering a compliance check into other engagements. When building a case for outside IR35 status, evidence of genuine self-employment indicators is essential. This includes contracts that explicitly provide for substitution, demonstrable financial risk through investment in equipment or training, lack of mutual obligation where the client is not obliged to offer work and the contractor is not obliged to accept, control over working hours and methods, and multiple clients served simultaneously. HMRC's Check Employment Status for Tax (CEST) tool provides an indication of status, though it has been widely criticised for producing inaccurate results in borderline cases. Many contractors engage specialist IR35 advisors to review contracts and working practices, which costs £500-2,000 but can save tens of thousands in tax if the determination is successfully overturned.

Using Our IR35 Status Calculator

Our IR35 determination calculator guides you through the key factors that HMRC considers when assessing employment status, providing an indication of whether a contract is likely to fall inside or outside IR35. The tool covers the main status tests including personal service, substitution, mutuality of obligation, control, financial risk, and integration with the client's business. While no online tool can provide a definitive determination, as each case depends on its specific facts and the contract as operated in practice, our calculator highlights the areas of strength and weakness in your IR35 position. It also estimates the financial difference between inside and outside IR35 treatment, showing the tax and NI savings at stake. Always seek professional advice for complex or borderline cases, and ensure your contracts accurately reflect your genuine working practices.