How IR35 has reshaped the economics of the UK contracting market

IR35 has affected UK contractors for more than 25 years, but the biggest change came when the government shifted responsibility for status decisions away from contractors and onto clients.

The public sector reforms took effect in 2017, followed by the private sector in 2021. Since then, medium and large organisations have usually had to decide whether a contractor falls inside or outside IR35.

Before 2021, a contractor working through a personal service company would normally assess their own IR35 position and account for any tax due. After the reform, many clients had to make that assessment themselves and could face the tax bill if they got it wrong.

Some businesses continued to assess contractors individually. Others stopped engaging limited company contractors altogether, moved roles onto payroll or required workers to use umbrella companies.

HMRC estimates that around 120,000 workers were affected by the 2021 reform and that around 45,000 fewer personal service companies were formed than historic trends might otherwise have suggested, according to its assessment of the private sector off-payroll reforms.

Why IR35 can make a contract much more expensive

The tax difference between an inside and outside IR35 contract can be substantial, particularly at typical professional contractor rates.

Take a contractor charging £500 a day for 220 days a year. That gives a headline contract value of £110,000.

An outside-IR35 contractor can receive that income through their company, deduct legitimate business costs, pay Corporation Tax on the resulting profit and extract funds through salary and dividends.

An inside-IR35 engagement works very differently. PAYE Income Tax and employee National Insurance apply to the deemed employment income, while employer's National Insurance also has to be funded somewhere in the chain.

For 2026/27, the main employee National Insurance rate is 8%, falling to 2% above the upper earnings limit. Employer's National Insurance is 15%.

On a £110,000 contract, employer's NI alone can run to roughly £14,000 to £15,000 before allowing for the precise payroll structure.

The client may absorb that cost. An agency may build it into the rate. An umbrella company will normally calculate its employment costs from the assignment rate before arriving at the worker's gross taxable salary.

Contractors therefore need to look beyond the headline day rate when comparing opportunities. A £500-a-day outside-IR35 contract and a £500-a-day umbrella assignment are not financially equivalent.

That is one reason contractors often negotiate higher rates for inside-IR35 work.

IR35 has encouraged different hiring models

The reforms also helped increase the use of umbrella companies.

For clients, an umbrella arrangement can remove the need to engage the worker's personal service company directly. The umbrella employs the worker and operates PAYE, although the off-payroll rules and wider supply-chain responsibilities can still require careful handling.

Many contractors now move between limited company and umbrella assignments depending on the client, the status assessment and the rate on offer.

Contractors who continue to work through their own companies may also look at professional IR35 protection to help with the cost of an HMRC enquiry or professional representation, depending on the policy.

The wider UK contracting market still supports large numbers of independent professionals, particularly in IT, engineering, finance and other specialist sectors. But clients now pay much closer attention to employment status when they structure an engagement.

The status test remains complicated

IR35 does not depend on a contractor's job title, day rate or whether the contract describes them as self-employed.

The courts look at the relationship as a whole.

Personal service, substitution, control and mutuality of obligation remain central to the employment-status test. Other factors can also matter, including financial risk, the provision of equipment and whether the contractor genuinely operates a business on their own account.

The written contract matters, but the actual working arrangements matter too.

A carefully drafted substitution clause carries little weight if both parties know that the contractor could never send a substitute. Equally, a client checking that a project meets agreed specifications does not automatically give it the same degree of control that an employer exercises over an employee.

These distinctions explain why two contractors doing apparently similar work can receive different IR35 outcomes.

New IR35 resource launched

A new specialist site, IR35 Update, has launched to provide detailed guidance on the legislation, recent developments, case law and practical status issues.

The site also includes tools aimed at contractors, advisers and businesses dealing with the off-payroll rules.

Its founder, James Leckie, says the financial impact often gets lost in discussions about employment-status tests.

"People tend to talk about IR35 as though it is just a technical status question. For a contractor, it can alter the economics of an assignment quite dramatically. Once you bring PAYE and employer's National Insurance into a contract worth £100,000 or more, the numbers become very significant."

He also points to the effect on hiring decisions:

"Clients now have to think about IR35 before they engage somebody, not several years later if HMRC opens an enquiry. That has made status part of the commercial decision about how the work will be carried out and what rate the contractor will accept."

Contractors now price status into the deal

The private sector reform did not remove limited company contracting, and plenty of businesses still engage contractors outside IR35 where the working arrangements support that position.

But IR35 now affects negotiations much earlier.

Contractors compare inside and outside rates. Clients consider tax risk before approving a hiring model. Agencies and umbrellas have become more involved in the structure of the supply chain.

At £400, £500 or £600 a day, the tax treatment can change the value of a contract by thousands of pounds over a year, so status now forms part of the commercial calculation before anyone signs.