What Is a Status Determination Statement and Why Does It Matter for Web Developers?
A status determination statement (SDS) is the document you must issue to any contractor engaged through an intermediary (their own limited company or umbrella company) before work starts. It tells them whether, for tax purposes, they would be inside or outside IR35.
If you run a digital agency, a creative agency, or a web design agency, you almost certainly engage web developers on this basis. Maybe you bring in a front-end developer for a six-month project build. Maybe you have a back-end specialist on retainer for ongoing maintenance. Either way, you need an SDS on file.
The off-payroll working rules (commonly called IR35) apply to medium and large agencies. If your agency meets two of these three conditions, you are caught: annual turnover over £10.2m, balance sheet over £5.1m, or more than 50 employees. Most agencies billing over £1m will be medium or large under these tests.
This guide walks you through writing a compliant status determination statement for a web developer engagement. We will cover what to include, the tests you must apply, and the common mistakes that get agencies into trouble.
The Three Tests That Determine IR35 Status for a Web Developer
HMRC looks at three core factors when deciding whether a contractor is genuinely self-employed or effectively an employee. You must assess all three before you issue the SDS.
Substitution and Personal Service
Can the web developer send someone else to do the work? A genuine contractor has a right of substitution. If the contract says the developer must turn up personally, that points to employment. If the developer can send a competent replacement when they are unavailable, that points to self-employment.
In practice, for web developers, this is often the weakest area. Most clients want a specific developer because they know the codebase, the tech stack, or the client relationship. If you insist on personal service, you need to be honest about it in the SDS. Do not pretend there is a substitution right if you would never accept a substitute.
Control
Who decides how the work gets done? If you tell the web developer what hours to work, what tools to use, and how to structure their day, you are exerting control. That points to employment.
If you specify the outcome (build this API endpoint, deliver this feature by Friday) and leave the developer to decide how to achieve it, that points to self-employment. Most web developer engagements fall somewhere in the middle. You might specify the tech stack (React, Node, AWS) because that is what your existing codebase uses. That is fine. But if you also dictate the developer's working hours and insist they attend your daily stand-ups in person, control shifts towards employment.
Mutuality of Obligation (MOO)
Is the client obliged to offer work, and is the contractor obliged to accept it? A permanent employee has ongoing mutuality. A contractor on a fixed-term project does not. When the project ends, the relationship ends.
For web developers, MOO is usually straightforward if you are hiring for a specific project with a defined scope and end date. Problems arise when you keep extending the contract or moving the developer from one project to another without a break. HMRC sees that as ongoing employment in all but name.
What to Include in a Status Determination Statement for a Web Developer
An SDS is not a long document. HMRC requires it to contain specific information. Here is what you need to cover.
1. The Engager's Details
Your agency name, address, and company number. If you are using an umbrella or a recruitment agency as the fee-payer, include their details too.
2. The Contractor's Details
The web developer's name and the name of their personal service company (PSC) or umbrella company.
3. The Engagement Details
A brief description of the work. For example: "Front-end web developer for the redesign of client X's e-commerce platform. Estimated duration: 4 months. Deliverables: React component library, integration with Shopify API, responsive templates."
Be specific. Vague descriptions weaken your position if HMRC challenges the determination later.
4. The Determination
State clearly whether the engagement is inside or outside IR35. Do not use weasel words. "Inside IR35" or "Outside IR35" is sufficient.
5. The Reasons
This is the most important section. You must explain why you reached that conclusion. Reference the three tests above and show your reasoning for each one.
A good reason section for an outside-IR35 web developer might read:
"Substitution: The contractor has an unrestricted right to provide a substitute, subject only to reasonable competency checks. The contractor has identified two potential substitutes with equivalent React experience.
Control: The contractor determines their own working hours and location. The agency specifies deliverables and deadlines but does not direct how the work is performed. The contractor uses their own equipment and development environment.
Mutuality of Obligation: The engagement is for a fixed-scope project with defined deliverables. There is no obligation on either party to offer or accept further work beyond the project scope."
6. The Date and Sign-off
Include the date the determination was made. The SDS must be issued before the engagement begins. If you issue it after work has started, you have already breached the rules.
A Practical Template for a Web Developer SDS
Here is a template you can adapt. Fill in the bracketed sections with your specific details.
Status Determination Statement
Engager: [Your Agency Name Ltd], [Company Number], [Registered Address]
Contractor: [Developer Name], trading as [PSC Name Ltd], [Company Number]
Engagement: [Brief description of the web development project, duration, and deliverables]
Determination: This engagement is determined to be [Inside / Outside] the scope of the off-payroll working rules (IR35).
Reasons for Determination:
Substitution: [Explain the substitution clause and whether it is genuine]
Control: [Explain who controls how, when, and where the work is done]
Mutuality of Obligation: [Explain whether there is an ongoing obligation to offer or accept work]
Additional Factors Considered: [Optional: mention financial risk, equipment, or other relevant factors]
Date of Determination: [DD/MM/YYYY]
Signed: [Name and role of person making the determination at your agency]
What Happens If the Web Developer Disagrees With Your SDS
The contractor has the right to challenge your determination. If they disagree, they must write to you setting out their reasons. You then have 45 days to respond. If you change your determination based on their challenge, you must issue a new SDS and notify the fee-payer.
This does not happen often, but it does happen. Most disagreements come from contractors who believe they are outside IR35 but have been determined as inside. They may be right. If you have not done the assessment properly, they will spot the gaps.
If you receive a challenge, take it seriously. Review the contract and the working practices again. If the contractor is right, change the determination. If you stand by your original decision, explain why in writing within the 45-day window.
Common Mistakes Agencies Make With Web Developer SDS
We see the same errors repeatedly when reviewing SDS documents for our agency clients. Here are the ones to avoid.
Copying and Pasting From a Template Without Adapting It
A generic SDS is worse than no SDS. If HMRC reviews your file and sees a template that clearly was not tailored to the specific engagement, they will assume you did not do the assessment properly. Every SDS must reflect the actual working practices of that specific web developer.
Ignoring the CEST Tool
HMRC's Check Employment Status for Tax (CEST) tool is not perfect, but it is the only tool HMRC will stand by. If CEST says the engagement is outside IR35 and you have answered the questions honestly, HMRC will not challenge that determination. Use CEST as part of your process, but do not rely on it entirely. For complex web developer engagements, CEST can give unreliable results.
Determining Inside IR35 When the Contractor Is Genuinely Outside
Some agencies default to "inside IR35" for every contractor to avoid the risk of a challenge. That is lazy and costly. It pushes the tax burden onto the contractor and makes it harder for you to attract good developers. Do the assessment properly. If the developer is genuinely outside, say so.
Failing to Document Working Practices
Your SDS should reflect what actually happens, not what the contract says. If the contract says the developer has control over their hours, but in practice you expect them in the office every day from 9 to 5, the SDS must reflect the reality. HMRC will look at working practices, not just the written contract.
How Agency Founder Finance Can Help
We work with agency founders across the UK who engage web developers, designers, copywriters, and other contractors. As ICAEW qualified accountants, we review your contractor engagements, help you draft compliant SDS documents, and advise on IR35 risk before HMRC comes knocking.
If your contractor mix has changed in the last 12 months, or you are about to bring on a web developer for a major project, get in touch. We will review your current SDS process and make sure you are covered.
For more on IR35 and contractor management, see our Contractors and IR35 section. And if you run a web design agency, we have specific guidance on the common contractor roles in your sector.