IR35 Status Estimator
Contractor Calculator's IR35 Status Estimator uses key indicators from HMRC's CEST (Check Employment Status for Tax) criteria to give you an initial indication of whether your engagement is likely inside or outside IR35. Answer the 10 questions below about your actual working arrangement.
How is this calculated?
The estimator evaluates 10 key factors that courts and tribunals have used to determine employment status. Each factor either indicates self-employment (outside IR35) or employment (inside IR35).
The three most important tests are: Substitution (can you send someone else to do the work?), Control (does the client control how, when, and where you work?), and Mutuality of Obligation (must the client offer work and must you accept it?).
The result is based on the balance of indicators. A strong majority pointing one way gives a clearer result; a mixed picture produces an uncertain outcome.
If you're outside IR35, our Compare Structures calculator shows the tax advantages of the limited company structure. Use our Dividend vs Salary Calculator to optimise your income extraction.
Frequently Asked Questions
Am I inside or outside IR35?
Your IR35 status depends on the actual working practices of your engagement, not just the contract terms. Key factors include whether you have a right of substitution, the degree of client control over your work, and whether there is mutuality of obligation. Use the estimator above for an initial indication, but always seek professional advice for a definitive determination.
What is IR35 and how does it affect UK contractors?
IR35 is UK tax legislation that determines whether a contractor is genuinely self-employed or effectively an employee for tax purposes. If you are inside IR35, you must pay tax and National Insurance as if you were an employee, significantly reducing your take-home pay. If outside IR35, you can benefit from the more tax-efficient limited company structure.
What is the CEST tool and should I use it?
CEST (Check Employment Status for Tax) is HMRC's official online tool for determining IR35 status. While HMRC stands behind its results, many tax professionals argue it does not adequately consider all relevant factors, particularly mutuality of obligation. It is one data point but should not be your only assessment.
Who is responsible for determining IR35 status?
For medium and large private sector clients (and all public sector clients), the end client is responsible for determining IR35 status under the off-payroll working rules. For small private sector clients, the contractor's own company (PSC) remains responsible for the IR35 determination.
What happens if I am inside IR35?
If inside IR35, the fee-payer (usually the agency or client) must deduct Income Tax and employee National Insurance from your payments, and pay employer National Insurance. This means your take-home pay will be similar to a permanent employee. You can still deduct 5% of gross income as an allowable expense.
Can I appeal an IR35 determination?
Yes. If you disagree with a client's IR35 determination, you can use the client's internal disagreement process. If unresolved, you can appeal to HMRC. It is important to have a properly reviewed contract and clear evidence of your actual working practices to support any appeal.
These calculations are estimates based on current published tax rates. They do not constitute financial, tax, or legal advice. Always consult a qualified accountant for your specific situation.
Tax rates sourced from HMRC published rates for the 2025/26 tax year. Last verified: March 2026.