IR35 Guides for UK Contractors

Mutuality of Obligation is a foundational IR35 test that HMRC deliberately excluded from CEST. Here is what it means, why it matters, and how to use it in a dispute.

A right of substitution can put you outside IR35, but only if it is real. What Ready Mixed Concrete, Autoclenz and Atholl House actually established.

Who decides your IR35 status: your client, your limited company, or HMRC? How the off-payroll rules assign responsibility, and when the raised small company thresholds actually start to move it.

The Atholl House IR35 case took Kaye Adams nine years to win. Here is what it established about being in business on your own account and why it matters.

CEST and a tax tribunal can reach opposite IR35 answers. The PGMOL case shows why, and what an Outside, Inside or Undetermined result means.

Your IR35 contract might say outside. Your working practices might say inside. Autoclenz established which one wins, and it is not always the paperwork.

Being pushed inside IR35? Here is what actually changes, what you can do about it, and how to model the real financial impact before you decide.

PGMOL is two rulings, not one: the 2024 Supreme Court decision on mutuality and control, and the 2026 First-tier Tribunal verdict on the referees' actual status. Here is what each one decided.

An honest comparison of IR35 Verdict, IR35 Shield, Qdos, Kingsbridge and Contractor Calculator, and where each one actually fits.

A salary sacrifice pension inside IR35 can claw back much of the umbrella tax hit. See how it works and model your own numbers across three scenarios.

Seeing employer NI taken from your day rate through an umbrella? Here is the statutory mechanism, why it happens, and whether it is actually legal.

The best IR35 calculators compared: what each one actually models, where they fall short, and why the salary sacrifice scenario changes everything.

Confused by your umbrella payslip? See exactly where your day rate goes: employer NI, the apprenticeship levy, margin, PAYE tax and employee NI.

IR35 insurance has no single market price. Qdos and Roots publish annual premiums, Markel Tax prices per engagement via brokers, and Kingsbridge publishes no price at all. Here is what each one actually charges.

HMRC can open an IR35 investigation years after a contract ends. Here is what determines the size of that exposure: the lookback window, defence costs, and the tax liability if HMRC wins.

IR35 insurance covers HMRC enquiry defence costs and, with the right policy, your tax liability too. Here is exactly what is included and what is not.

The three main IR35 insurance providers profiled: Qdos, Kingsbridge, and Markel Tax. What each policy covers, what it costs, and how you access it.

Being outside IR35 does not eliminate risk. HMRC can investigate past years, and your client's SDS may conflict with your own position. Here is what determines whether that risk applies to you.

The small company thresholds rose in April 2025, but the off-payroll consequence does not arrive until 6 April 2027 at the earliest. Here is the lookback mechanism that creates the lag, and why the April 2026 date circulating widely is wrong

IR35 rules 2026 explained in plain English: who decides your status, the April 2026 threshold and umbrella changes, and how to know where you stand.