Receiving a Status Determination Statement that says you are inside IR35 can knock thousands of pounds off your take-home, so it pays to know exactly what the document is, what makes it valid, and what you can do if you think the client has got it wrong. The off-payroll working rules give contractors a specific set of rights here, including a 45-day window for the client to reconsider, and they place real obligations and real liability on the client that issues the determination.

This guide sets out what a valid SDS must contain, what reasonable care means in practice, when the liability moves up the chain to the client, and how to use the client-led disagreement process. It covers the rules that apply when your end client is medium or large, which is the situation most limited-company contractors find themselves in for 2026/27.

Where the SDS sits: Chapter 10 versus Chapter 8

Two related but separate sets of rules sit in Part 2 of the Income Tax (Earnings and Pensions) Act 2003. The original intermediaries legislation, the one most people mean when they say "IR35", is Chapter 8. The off-payroll working rules are Chapter 10. The SDS is purely a Chapter 10 concept, so it only exists when Chapter 10 applies.

The dividing line between the two is the size of your end client. Where the client is small, or wholly overseas with no UK connection, Chapter 8 applies and your personal service company assesses its own status and, if inside, operates a deemed employment payment on its own account. Where the client is medium or large, Chapter 10 applies: the client determines status by issuing an SDS, and the fee-payer (usually the agency closest to your company) operates PAYE and National Insurance before paying your company.

This is the single most important thing to grasp about determinations. Under Chapter 10, the end client decides your status, not you. The loose idea that a contractor "always decides their own IR35 status" is only true under Chapter 8, where the client is small or overseas. For a fuller treatment of the two regimes, see our guide to what IR35 is and how Chapters 8 and 10 differ.

When might my client be small enough to fall outside Chapter 10?

"Small" for off-payroll purposes uses the Companies Act 2006 section 382 small-company conditions, imported into the off-payroll rules by ITEPA section 60A. A company is small for a financial year if it meets two or more of three conditions. From financial years beginning on or after 6 April 2025 those thresholds were raised by roughly half: turnover not more than £15m (up from £10.2m), balance sheet total not more than £7.5m (up from £5.1m), and not more than 50 employees (unchanged).

It is tempting to assume the higher thresholds take a lot of clients out of scope straight away, but the timing rules say otherwise. A company normally has to meet (or stop meeting) the conditions across two consecutive financial years before its status changes, and a client's obligation for a given tax year is set by reference to its last financial year that ended before that tax year began, with time to file. Because of this lag plus the two-year rule, the earliest a previously medium client can drop out of Chapter 10 scope on the back of the raised thresholds is 6 April 2027, and for many year-ends 6 April 2028. So for 2026/27, assume your medium or large clients are still in scope and will still be issuing you an SDS unless the client has confirmed otherwise. Our guide to the small-company exemption works through the timing in detail.

What a valid SDS must contain

An SDS is not just a yes or no. Under ITEPA section 61NA, a valid SDS has two essential elements:

  • A conclusion, stating whether the engagement is inside or outside IR35 (that is, whether you would be regarded as an employee for tax if you worked directly rather than through your company).
  • The reasons for that conclusion. The client must explain the basis for its decision, not simply assert the outcome.

Both elements must be reached with reasonable care, and the SDS must be passed to two recipients: the worker (you) and the next party in the labour-supply chain (the agency or fee-payer below the client). A statement that gives a conclusion with no reasons, or that is produced without proper attention to the facts, is not a valid SDS at all, and an invalid SDS carries consequences explored below.

The reasons matter for you as well as for the client. They are the starting point if you want to challenge the determination, because you can only argue effectively against a conclusion once you understand how the client reached it. A reasons section that simply repeats a CEST output, with no engagement with how you actually work, is a warning sign that the client may not have taken reasonable care.

Reasonable care: the obligation that decides who pays

Reasonable care is the linchpin of the whole regime, and it is worth being precise about what failing it does. Two distinct consequences flow from a client getting the SDS wrong:

  1. Failure to take reasonable care. If the client does not take reasonable care in reaching the determination, the SDS is invalid and the client itself becomes the deemed employer, liable for the PAYE and employee NIC (and employer NIC on top), even though an agency or other fee-payer sits below it in the chain. Carelessness does not just risk a wrong answer; it pulls the tax liability back up to the client.
  2. Failure to pass the SDS down. If the client fails to pass the SDS down the chain to the next party, the liability sits with the client until it does. The duty is not discharged simply by reaching a conclusion; the client has to communicate it correctly.

What does reasonable care look like in practice? It means actually examining the facts of the specific engagement: how the work is controlled, whether there is a genuine right of substitution, where the financial risk lies, and how the engagement operates day to day, then forming a conclusion on that basis and recording the reasons. HMRC's guidance (ESM10014) sets the expectation that the level of care should reflect the size and capability of the client; a large, well-resourced organisation is expected to do more than a one-off engager.

What does not count as reasonable care

HMRC's own guidance is clear that certain behaviours fall short. Determining status without proper consideration of the engagement, applying outcomes to groups of workers without thought, or relying on a tool whose answers do not reflect how the engagement really runs all point towards a failure of reasonable care. The most common failing, and the one most likely to affect you, is the blanket determination.

Blanket determinations: bad practice and legally risky

A blanket determination is where a client applies a single "inside IR35" label to a whole category of contractors, by role type, by department, or by contract type, without assessing each engagement individually. Some clients did this in the run-up to the April 2021 private-sector reform, treating every limited-company contractor as inside to avoid the effort and the risk of getting individual determinations wrong.

The firm's position is straightforward. A blanket determination made without individual assessment is very likely a failure of the reasonable-care requirement, because reasonable care means looking at the actual facts of each engagement rather than stamping a category. And because a careless determination invalidates the SDS and can move the deemed-employer liability to the client, blanket determinations are not the safe option some clients assume; they are bad practice and legally risky for the client itself.

There is an important nuance. A client is allowed to use reasonable, structured processes to make determinations more efficient across similar engagements, for example by grouping genuinely identical roles after assessing the facts that they share. What is not acceptable is applying a label to a group without ever assessing the relevant facts. The dividing line is whether the client has actually considered the engagement, or merely sorted it into a bucket.

If you have received an inside determination that you suspect was applied across the board rather than to your specific engagement, you are not stuck with it. The client-led disagreement process exists precisely so you can seek an individual assessment.

The 45-day client-led disagreement process

If you disagree with your SDS, ITEPA section 61T gives you a route to challenge it: the client-led disagreement process. The mechanics are these.

  • You (or the fee-payer) make representations to the client stating that you disagree with the determination and why.
  • The client must consider those representations and respond within 45 days of receiving them.
  • The response must either confirm the original SDS, with reasons, or provide a new SDS with a different conclusion that supersedes the first.

The process is "client-led", which has a specific meaning: the client, not an independent body or a tribunal, makes the decision. There is no statutory appeal to HMRC built into this process. But "client-led" does not mean the client can ignore you. The law requires the client to consider your points and to give reasons for its response, and there is a hard consequence for inaction: if the client does not respond within the 45-day period, it is treated as having failed to take reasonable care, which moves the deemed-employer liability to the client. So the 45-day clock is not a courtesy; it is backed by a liability shift.

How to make your representations count

Because the client looks at the engagement, and HMRC ultimately looks at the working practices, your representations are far stronger when they are grounded in how the work actually operates rather than in contract wording alone. Useful evidence includes:

  • Control: the extent to which you decide how, when and where you do the work, as opposed to being directed and line-managed like an employee.
  • Substitution: whether you have a genuine, unfettered right to send a substitute, paying that substitute yourself, that the client cannot unreasonably refuse.
  • Financial risk and being in business on your own account: your own equipment, professional indemnity insurance, the chance of profit or loss, and multiple clients.

These map onto the case-law tests that decide status: personal service, control and mutuality of obligation, weighed as a whole picture. For how those tests are applied, and how to evidence an outside position, see our guides to protecting outside IR35 status and what an inside IR35 determination means for your take-home.

A worked timeline

It helps to see how the pieces fit together over a single engagement. Suppose you start a six-month contract with a large client through an agency in 2026/27.

  1. Before or at the start of the engagement, the client assesses the facts and issues an SDS with a conclusion and reasons, passing it to you and to the agency.
  2. You review the reasons. The SDS says inside IR35, but the reasons are generic and do not mention your right of substitution or your control over the work, which suggests the conclusion may have been applied to your role type rather than to your actual engagement.
  3. You make written representations to the client, setting out, with reference to the real working practices, why you believe the engagement is outside IR35.
  4. The 45-day clock starts. The client must consider your points and respond within 45 days, either confirming the SDS with reasons or issuing a new one. If it stays silent past 45 days, it is treated as failing to take reasonable care and becomes the deemed employer.
  5. Meanwhile, the fee-payer operates on the current determination. If the SDS remains inside, the fee-payer continues to deduct PAYE and NIC until and unless a new SDS is issued.

One practical point: the disagreement process does not pause the deductions. While the SDS stands as inside, the fee-payer keeps operating it. That is one reason to raise a disagreement promptly and to keep good contemporaneous evidence of how the engagement runs.

What an inside determination actually costs you

If the determination is, and remains, inside IR35 under Chapter 10, the fee-payer treats the payment to your company, after deducting any VAT and the direct cost of materials, as a deemed direct payment. It operates PAYE and employee Class 1 NIC on that amount, and pays employer Class 1 NIC at 15% (above the £5,000 secondary threshold for 2026/27) and the Apprenticeship Levy on top, before paying the net to your company.

Two features are worth flagging. First, there is no 5% expenses allowance under Chapter 10. That flat administrative allowance exists only under Chapter 8 (the small or overseas-client route); it was abolished for off-payroll engagements, so an inside Chapter 10 determination gives you no equivalent deduction. Second, the income arrives in your company having already been taxed, so it can generally be drawn without a second charge, but the tax-efficient salary-and-dividend extraction you would normally use on company profit is lost on that income. The practical upshot is a materially lower take-home than an equivalent outside engagement.

If the client got it wrong: debt transfer and the offset

The reasonable-care and pass-it-down rules are reinforced by the off-payroll debt-transfer provisions. Where a party in the chain fails to meet its obligations or cannot pay, HMRC can recover the PAYE debt from another party further up the chain, ultimately the end client. So a client cannot fully insulate itself by pushing the determination down to an agency; if things go wrong below it, the liability can climb back up.

There is a counterweight that softens, but does not remove, the cost of a wrong "outside" determination. From 6 April 2024 a statutory set-off (often called the offset) lets HMRC reduce the deemed employer's PAYE liability by an estimate of the taxes the worker and the intermediary have already paid on the same income, such as corporation tax on company profits, income tax and employee NIC on salary, and income tax on dividends. This addresses the double-taxation problem that existed before April 2024, when HMRC assessed the full PAYE on the deemed employer without credit for tax already paid.

Two cautions. The offset reduces but does not eliminate the deemed employer's exposure, because it credits the worker and company taxes already paid, not the employer NIC, which was never paid in the first place. And it is an HMRC-operated estimate applied on a trigger event (typically a determination on or after 6 April 2024), not an automatic netting that the parties can simply rely on. The mechanics of the SDS chain, fee-payer and set-off are covered in our guide to the off-payroll working rules in the private sector.

CEST, contract reviews and the limits of paperwork

Many clients reach their determination with the help of HMRC's Check Employment Status for Tax (CEST) tool, updated on 30 April 2025 with a dedicated mutuality-of-obligation question and an upfront "is there a contract" gate. CEST has a legitimate role as a first screen and as an audit-trail document, and HMRC says it will stand behind a CEST result where the inputs are accurate, consistent with the working practices, in line with the guidance and absent any avoidance.

That promise has real limits, and it is worth keeping them in view whether you are reading an SDS that relied on CEST or building your own evidence. CEST does not bind a tribunal. It is only as reliable as the answers fed into it, so a determination that does not match the actual working practices is worthless. And its treatment of mutuality of obligation is narrower than the case law, which means it can return "outside", or decline to decide, on facts a tribunal might view differently. A CEST "outside" result is never a guarantee.

The same principle applies to contract reviews. A professional review of the written terms is worthwhile, but it is not sufficient on its own, because HMRC and the tribunals look at how the engagement actually operates. A clean contract sitting over employee-like working practices will not hold. The firm's consistent line is working practices over contract wording: review both the paperwork and the reality, and make sure they match.

Practical checklist when an SDS lands

  • Check it is a valid SDS: a conclusion plus reasons, passed to you and to the next party in the chain. No reasons means no valid SDS.
  • Read the reasons critically: do they engage with your specific engagement, or do they read like a blanket label applied to your role type?
  • Compare against your working practices: control, substitution, financial risk and whether you are genuinely in business on your own account.
  • If you disagree, make written representations and start the 45-day clock. Keep them grounded in how the work actually runs.
  • Keep evidence as you go: contemporaneous records of substitution rights, autonomy and risk are far more persuasive than recollections after the fact.
  • Watch the timing: the disagreement process does not pause deductions, so raise it promptly.

Where this leaves you

The SDS regime puts the determination, and the consequences of getting it wrong, on your end client. A valid SDS needs a conclusion and reasons, reached with reasonable care and passed down the chain. Carelessness invalidates the statement and makes the client the deemed employer; failure to pass it on keeps the liability with the client; and the debt-transfer rules mean the liability can climb up the chain to the client in any event. Blanket determinations sit squarely on the wrong side of the reasonable-care line, and the 45-day client-led disagreement process is your route to insist on an individual assessment.

If you have received an SDS you believe is wrong, or you want help evidencing an outside position before a determination is made, our team reviews determinations and working practices for contractors day in, day out. Take a look at our IR35 status review service or get in touch to talk through your engagement.