IR35 Off-Payroll Working Rules: Employer Compliance Guide 2026

IR35 off-payroll working rules remain one of the most complex and financially risky areas of UK payroll compliance for employers. Since the reforms shifted responsibility for determining employment status to medium and large businesses in April 2021, HMRC has intensified enforcement — and the penalties for getting it wrong can be severe, including backdated tax, National Insurance, and interest stretching back years.

This guide explains exactly how the off-payroll rules work, how to assess whether a contractor falls inside or outside IR35, and the practical steps you need to take to stay compliant in 2026.

Who do the off-payroll rules apply to?

The off-payroll working rules apply to any organisation that engages a worker who provides their services through an intermediary — typically a personal service company (PSC). The rules determine whether that worker would be an employee if they were engaged directly, and if so, require the end client to deduct Income Tax and National Insurance at source.

Since April 2021, the responsibility for making this determination sits with the end client rather than the contractor, provided the client is a medium or large organisation. Small companies are exempt and the contractor retains responsibility for their own status.

Understanding the intermediary chain

The rules affect three parties: the end client (your business), the intermediary (usually the contractor's PSC), and the worker themselves. If you are the end client and you are not a small company, you must issue a Status Determination Statement (SDS) for every contractor engaged through a PSC.

The SDS must be passed to both the contractor and the next party in the supply chain — typically the recruitment agency. The agency or the party paying the PSC is then responsible for making the tax deductions if the determination is "inside IR35."

How to assess contractor status

HMRC uses three primary tests to determine employment status, and your assessment must consider all of them:

Using CEST (Check Employment Status for Tax)

HMRC provides the free CEST tool to help make determinations. While HMRC says it will stand by CEST results, tribunals have occasionally disagreed with its outputs. Use CEST as a starting point, but document your reasoning thoroughly beyond the tool's output.

Issuing a Status Determination Statement

For every contractor engaged through a PSC, you must produce an SDS before the engagement begins or, for existing engagements, before the start of the new tax year. The SDS must include your conclusion (inside or outside IR35) and the reasons for reaching it.

The statement must be delivered to the worker and to the party you contract with (usually the agency). You must take reasonable care in making the determination — a boilerplate response will not satisfy HMRC.

What happens if a contractor disagrees

Contractors have the right to dispute your determination. When they do, you must respond within 45 days with either a revised SDS or confirmation of the original determination with reasons. Failing to respond within 45 days shifts the tax liability back to you as the end client, regardless of the actual employment status.

The dispute process step by step

1. Contractor receives your SDS and submits a written disagreement
2. You must acknowledge receipt and begin a review
3. Consider any new information the contractor provides
4. Respond within 45 days with your decision and detailed reasoning
5. If you change the determination, issue a new SDS to all parties in the chain

Penalties for non-compliance

Getting IR35 wrong carries significant financial consequences. If HMRC determines that deductions should have been made but were not, the liability flows up the chain to the party that failed in its obligations.

Practical compliance checklist

You should be doing all of the following for every contractor engagement through a PSC:

• Assess each engagement individually using CEST and your own analysis
• Document the reasoning behind every determination in writing
• Issue the SDS before the engagement begins
• Pass the SDS to both the worker and the next party in the chain
• Maintain a log of all determinations, including dates and recipients
• Have a formal process for handling disputes within the 45-day window
• Review existing determinations at least annually or when the engagement changes materially
• Ensure your accounts or payroll team knows how to apply deductions when a determination is "inside IR35"

Run your payroll numbers through our Payroll Tax Calculator to understand the financial impact of inside-IR35 determinations on your contractor costs.

The relationship between IR35 and employment rights

It is important to understand that an IR35 determination is a tax classification, not an employment law classification. A contractor determined as "inside IR35" for tax purposes does not automatically gain employment rights such as unfair dismissal protection, holiday pay, or pension entitlement. However, the overlap between the tests used by HMRC and those used by employment tribunals means that an inside-IR35 determination could support a worker's claim for employment status in a separate legal challenge.

For more on the distinction between employees and contractors, see our guide to employee vs contractor classification.

Key takeaways

IR35 compliance comes down to three disciplines: assess each engagement individually and honestly, document everything thoroughly, and respond to disputes within the 45-day window. The financial risk of getting this wrong is substantial — backdated tax, NI, interest, and penalties can accumulate rapidly across multiple contractors.

If you are engaging contractors through PSCs and are not a small company, this is not optional. Build the process into your onboarding workflow, review determinations regularly, and ensure your payroll team understands how to apply inside-IR35 deductions correctly. Use our Payroll Tax Calculator to model the cost impact, and review our P11D and benefits in kind guide for related compliance obligations.