What it is
IR35 is the shorthand recruiters and contractors use for the UK's intermediaries legislation, tax rules that target 'disguised employment': a worker who operates through their own limited company (a personal service company, or PSC) but works in a way that looks, in practice, like an employee of the end client. If HMRC would view the relationship as employment were the intermediary stripped away, the engagement is 'inside IR35' and taxed accordingly. If the contractor genuinely operates with the control, substitution rights and financial risk of an independent business, it is 'outside IR35'.
Since April 2017 for public sector clients and April 2021 for medium and large private sector clients, the Off-Payroll Working rules moved responsibility for making that call from the contractor's own company to the end client. The client must issue a Status Determination Statement (SDS) for each engagement, stating the outcome and the reasoning, and pass it down the supply chain. Small private sector clients, those below a size threshold on turnover, balance sheet and employee count, are exempt, so a contractor working for a genuinely small client still self-assesses their own status.
IR35 status is decided once, by the client, but the liability for getting it wrong can land on whoever pays the invoice.
Why it matters
For a recruitment agency, IR35 status is not an academic tax question, it changes who is on the hook. Where an agency sits between the client and the contractor and pays the contractor's company directly, the agency is usually the 'fee-payer'. If the role is inside IR35, the fee-payer deducts PAYE income tax and National Insurance before the contractor is paid, and carries the liability if the SDS was never passed on or the deductions were handled incorrectly. Getting this wrong is not a paperwork slip, it is a direct financial exposure for the agency.
It also changes the commercial conversation before a role is even filled. An inside-IR35 day rate has to absorb PAYE tax, employee and employer National Insurance and the Apprenticeship Levy, so it needs to be structured differently from an outside-IR35 rate to deliver a comparable return to the contractor. Umbrella companies complicate this further: they employ the contractor directly and run PAYE regardless of the underlying determination, and from April 2026 agencies carry joint liability for PAYE if an umbrella company they've placed a worker with fails to account for it correctly. None of this is optional detail on a contract desk, it sits inside terms of business and the job order from the first conversation.
How boilr handles it
boilr does not make IR35 determinations, that judgement sits with the end client and, where relevant, the agency's own compliance process. What it does is stop the commercial facts from getting lost between the first conversation and the placement. When a job order is contract or interim, boilr keeps IR35 status, fee-payer arrangements and umbrella or PAYE routing attached to the mandate inside terms of business, so a consultant working the role six weeks later is working from the same facts as the one who opened it.
That knowledge sits in the Company Brain rather than in one consultant's inbox, so if a client has a settled position, most roles inside IR35, or a preference for a particular umbrella panel, it survives a desk change instead of being rediscovered on every new vacancy. Contract mandates stay visible in the BD pipeline alongside permanent roles, so a desk running both doesn't need a separate spreadsheet to track which is which.
