Cest Tool 2026 Update , How It Now Reads Mutual Obligation
- Atlas Tax
- 15 hours ago
- 16 min read
CEST Tool 2026 Update: How HMRC Now Reads Mutual Obligation , and Why It Still Falls Short
The CEST tool was updated on 30 April 2025 and now explicitly addresses mutuality of obligation (MOO) for the first time, adding a gating question that asks whether a contract is or will be in place before the assessment can proceed. For the 2026/27 tax year, the updated CEST sits alongside a significant change to the company size thresholds that determines who is even subject to the off-payroll working rules, making this a particularly important moment to understand what the tool does and does not do.
The short answer: CEST handles MOO more honestly than before, but the underlying logic has not changed. If you are a contractor, a personal service company (PSC) director, or a business engaging freelancers, you cannot rely on CEST alone.
What Is Mutuality of Obligation and Why Has It Caused So Much Trouble?
Mutuality of obligation has been one of the three tests that courts and tribunals use to determine whether a working arrangement amounts to employment. The other two are control and the right of substitution. In broad terms, MOO asks whether the engager is obliged to offer work, and whether the worker is obliged to accept it. The classic view held that a truly self-employed person could turn down work without consequence, and that no ongoing expectation existed between projects.
HMRC's position has always been more compressed than that. In its Employment Status Manual, HMRC takes the view that where any contract exists, a basic level of mutuality is already present: the worker agrees to perform the work and the engager agrees to pay for it. On that basis, HMRC never saw MOO as a meaningful discriminator in the CEST assessment. If a contract existed, the minimum threshold was met. The tool simply assumed MOO and moved on.
That approach was criticised for years, because tribunals have consistently applied a more nuanced test. The question was not merely whether any obligations existed, but whether the nature and extent of those obligations resembled employment. An engagement tied to a fixed deliverable, with no expectation of further work afterwards, sits in a very different position from one where a contractor has spent two years working on-site as part of an embedded team, with one project rolling into the next.
The Supreme Court's 2024 ruling in Professional Game Match Officials Ltd v HMRC clarified matters significantly, though not in the way many contractors had hoped. The Court confirmed that the "wage-work bargain" , agreeing to do the work and agreeing to be paid , is sufficient to establish the basic level of MOO. There does not need to be an overarching obligation to offer or accept future work. On the facts in PGMOL, the football referees accepted matches on a match-by-match basis, and once accepted, obligations existed for that engagement. The absence of an obligation to take future matches did not eliminate MOO during the active engagement.
That ruling initially looked like a win for HMRC. But when the case returned to the First-tier Tribunal for the fact-finding exercise the Supreme Court had directed, the tribunal found in PGMOL's favour: the referees were not employees. The obligations were narrow, short-lived, and heavily shaped by personal choice. The engager had no meaningful day-to-day control over how the referees conducted themselves on the pitch. So PGMOL ultimately prevailed, but the legal framework it established tells contractors something important: arguing that MOO does not exist at all is unlikely to succeed. What matters is the character and extent of those obligations, and how they sit alongside the control and substitution analysis.
What the April 2025 CEST Update Actually Changed
The tool that now applies in 2026/27 was refreshed by HMRC on 30 April 2025. The update was long overdue , the previous version dated from 2019 , and there had been genuine industry pressure to incorporate post-2022 case law, particularly the Atholl House Court of Appeal decision and the PGMOL Supreme Court ruling.
The principal visible change is the new upfront question: "Do you have or will there be a contract in place?" If the answer is no, the tool stops. This acknowledges that MOO requires a contractual basis, and it reflects the PGMOL principle that the wage-work bargain is the foundation of mutual obligation. Previously, CEST simply assumed a contract existed and carried a disclaimer at the front. The new approach makes the point explicit rather than implied.
Beyond that gateway question, the tool has been restructured into up to six sections, each addressing a different dimension of the relationship. Users can review and amend their answers at the end of each section, which reduces the risk of getting locked in by an early response. The guidance on personal service and financial risk has been rewritten for clarity. There are new links into HMRC's Employment Status Manual. And HMRC published for the first time a logic matrix, a spreadsheet showing the 72 possible outcome routes through the tool, of which 34 lead to the "unable to determine" result.
That last point is worth pausing on. Nearly half of all possible outcome routes lead to no answer at all. CEST does not determine employment status in a large proportion of genuine cases; it simply returns a verdict of "unable to determine" and leaves the engager to exercise their own judgement.
What did not change is the underlying logic: the weighting of tests, the treatment of substitution, and the fundamental assumption about MOO. HMRC confirmed this explicitly. A contractor running through the new CEST on an engagement they had already assessed under the old version would get the same result. The update was a restructuring of the user experience and a clarification of guidance, not a recalibration of the assessment itself.
Most industry commentary described the changes as cosmetic. That may be slightly harsh , the published logic matrix is genuinely useful, and better navigation does reduce errors , but the core criticism holds. The tool still places disproportionate weight on the right of substitution, still does not probe the ongoing nature of mutual obligations in any depth, and still cannot reach a determination in a significant number of real engagements.
The 2026/27 Context: Who Actually Needs to Use CEST Now?
This matters more in 2026/27 than it has for some years, because the company size thresholds changed on 6 April 2026.
Under the off-payroll working rules introduced in the private sector from April 2021, responsibility for determining IR35 status sits with the end client (the business receiving the contractor's services), not with the contractor's PSC, but only where the end client is medium or large. Small companies have been exempt since the rules came in. Until now, a company was small if it met at least two of three criteria: turnover not exceeding £10.2m, balance sheet total not exceeding £5.1m, and not more than 50 employees on average.
From 6 April 2026, two of those three thresholds have increased. The turnover limit is now £15m. The balance sheet total is now £7.5m. The employee headcount limit stays at 50. The consequence is that approximately 14,000 businesses that were previously medium-sized (and therefore in scope of the off-payroll rules) now qualify as small, and are therefore out of scope.
For those businesses and for the contractors they engage, the IR35 responsibility reverts to the contractor's PSC. The contractor determines their own status, operates their own tax affairs through their company, and carries the compliance risk. That is the position that applied to all private sector engagements before April 2021, and it requires the contractor to make a genuine, defensible assessment , one that CEST can support but cannot complete on its own.
For engagements with businesses that remain medium or large (turnover above £15m, or balance sheet above £7.5m, with more than 50 employees), the client must issue a Status Determination Statement (SDS) and take reasonable care in reaching it. CEST remains an acceptable tool to support that process. HMRC has confirmed it will stand by a CEST outcome where the information provided is accurate and in line with its guidance, and where the working arrangement is not a contrivance designed to produce a specific result.
How CEST Reads MOO in 2026/27: The Practical Picture
Running CEST today, the MOO question presents early in the process. The user confirms a contract exists. The tool then proceeds to the substantive sections covering personal service and substitution, control, financial risk, and the worker's business structure.
What the tool does not do is probe the nature of those mutual obligations. It does not ask whether the engagement is project-specific or open-ended. It does not ask whether there is an expectation of renewal. It does not ask whether the contractor has worked for the same client continuously for an extended period, or whether the client's teams treat the contractor as part of the furniture. All of those factual matters can be determinative in tribunal, yet none of them feature in the CEST questions.
This gap matters in practice. A construction contractor engaged through their limited company to complete a specific phase of a development project in Salford , with a defined scope, a start and end date, no guarantee of further work, and no obligation to be on site other than when relevant to the project , has a very different MOO profile from a software developer who has been embedded full-time with the same financial services firm for three years, working within their teams, using their equipment, and rolling from contract to contract without meaningful break. CEST would ask both of them the same MOO question and treat the answer the same way.
The PGMOL outcome at the First-tier Tribunal is instructive here. Even where the basic wage-work bargain exists, a tribunal will look closely at whether obligations were narrow and episodic or broad and continuous. Contractors with genuinely project-based, output-driven engagements have a defensible position. Those who are effectively permanent employees in all but name do not, regardless of what their contract says.
What a Reasonable Assessment Looks Like
CEST is a starting point, not a determination. Using it carefully is reasonable; treating its output as conclusive is not. HMRC will stand by the result, but only if the information provided is accurate. If a compliance check reveals that the actual working arrangements differed materially from what was entered into the tool, the CEST result offers no protection.
A proper assessment in 2026/27 should start with the actual contract and then test it against the actual working arrangements. Courts and tribunals have consistently said the written contract matters, but so does the day-to-day reality. Where the two diverge, the reality takes precedence. The substitution clause that no contractor has ever exercised, the right of direction that exists on paper but is never invoked , these carry much less weight than they appear to.
On MOO specifically, the questions worth answering in writing are: Is this engagement tied to a specific deliverable or is it indefinite? Does the client have an expectation of the contractor's continued availability beyond the current statement of work? Can either party end the engagement without financial consequence? Are there obligations in place between active phases of the project?
The cleaner the answers to those questions, the stronger the outside IR35 position. Where the answers are equivocal, the risk is real, and a specialist IR35 review rather than a CEST run is the appropriate response.
For contractors newly freed from client-side determination because their client has now dropped below the small company threshold, this is not a relaxation. It is a transfer of responsibility. HMRC has signalled that it will increase compliance activity in exactly these situations. A contractor who spent 2025/26 being assessed by their medium-sized client, and who now finds their new-small client disclaiming any obligation to determine status, should not assume that the previous CEST results carry forward into 2026/27. If the engagement has continued materially unchanged, the same analysis applies. It should be redone properly.
Key Takeaways for 2026/27
The CEST update acknowledged MOO but did not fix the tool. The April 2025 refresh introduced a gateway question on the existence of a contract, reflecting the PGMOL Supreme Court principle that the wage-work bargain is the baseline of mutual obligation. However, the underlying logic and weighting of factors has not changed.
The small company threshold change from 6 April 2026 is the bigger practical development for many contractors. Approximately 14,000 businesses now qualify as small and are out of scope of the off-payroll rules. Contractors working with those businesses must now determine their own IR35 status.
CEST returning "outside IR35" does not guarantee safety if the actual working arrangements look like employment. HMRC assesses working practices, not questionnaire answers. The MOO gap in CEST means ongoing, embedded engagements can score outside IR35 in the tool but remain exposed in a compliance investigation.
Project-based, output-driven, time-limited engagements are the strongest ground. The PGMOL First-tier Tribunal outcome confirms that narrow, episodic obligations with genuine choice on both sides support self-employment. That needs to be evidenced in contracts and in practice.
A CEST result is not a substitute for a documented, reasoned assessment. Where engagements are substantial, long-running, or ambiguous, a specialist review provides a far more defensible position than a tool that reaches no conclusion in almost half of all scenarios it can encounter.
FAQs
Q1: Does the new CEST gateway question on contracts mean HMRC has finally accepted that mutual obligation can be absent in some engagements?
A1: Not quite, and this is a distinction worth getting right. The new upfront question , asking whether a contract is or will be in place , is best read as a threshold filter rather than a concession on the legal debate. If there is no contract, the tool cannot run, because without any agreement at all there is nothing for CEST to assess. What HMRC has not done is acknowledge that mutual obligation can be absent once a contract exists. The position in the Employment Status Manual remains that the wage-work bargain (agreeing to do the work and agreeing to be paid) is enough to establish the basic level of mutual obligation. The gateway question reflects the Supreme Court's reasoning in PGMOL , that MOO exists once a contract is in force , rather than opening a door to argue that MOO is absent in a live engagement. Contractors who have been hoping HMRC would retreat from its position on MOO will not find that comfort in this update.
Q2: Can a contractor use the CEST result from a previous tax year as evidence of their status in a new tax year if the engagement has continued without interruption?
A2: The short answer is no, not without checking. HMRC has confirmed that pre-update CEST results remain valid where the information was accurate and the working arrangements have not changed materially. But "not changed materially" is doing a lot of work in that sentence. If the same contractor is still working with the same client a year later, performing the same tasks, the practical reality of the engagement may well have shifted even if the contract paperwork has simply been renewed. Tribunals look at the totality of the relationship. An engagement that started as project-specific but has gradually become embedded, open-ended, and effectively permanent carries a very different risk profile than it did at the outset. The safest approach is to re-run the assessment , whether through CEST or a more thorough specialist review , each time a contract is renewed or extended. This is especially relevant for the 2026/27 tax year given the small company threshold change, which has transferred self-determination responsibility back to contractors working with newly reclassified small clients.
Q3: If a client now qualifies as small from 6 April 2026 and tells a contractor it no longer needs to issue a Status Determination Statement, what should the contractor do?
A3: The client is technically correct: small companies are not required to issue an SDS under the off-payroll working rules, and their contractors' PSCs carry the self-determination responsibility. But the contractor should not treat this as a free pass. The change transfers the obligation; it does not remove it. The PSC must now genuinely assess whether the engagement falls inside or outside IR35, and that assessment needs to be defensible if HMRC comes asking. In practice, this means working through the substantive tests , control, substitution, MOO in its proper sense , and documenting the reasoning. HMRC has signalled it will increase compliance focus precisely in situations where responsibility has moved. A contractor who spent the previous tax year relying on a client-issued "outside" SDS and simply assumes that status continues in 2026/27 without fresh assessment is taking a real risk. Get the assessment done and written down before the next payment lands in the PSC's account.
Q4: Is it possible to have a CEST result of "outside IR35" for a specific engagement and still be challenged by HMRC?
A4: Yes, and this catches people out more often than it should. HMRC's commitment to stand by CEST results is conditional. The two principal conditions are that the information entered into the tool was accurate, and that the arrangement is not a contrivance designed to produce a particular outcome. If an HMRC compliance check reveals that the actual day-to-day working arrangements differed materially from what was described in the tool , for instance, that the client directed the contractor daily despite the "no control" answer on CEST , the determination is effectively void. The tool only knows what it was told. Where the written contract says one thing and the working reality says another, tribunals consistently prefer the reality. So an "outside" result is not a shield; it is an indication of how HMRC will treat an honest, accurate assessment. Keeping a contemporaneous record of working practices , when you worked, how directions were given or not given, how billing was structured , is far more protective than the CEST printout on its own.
Q5: How does CEST handle the situation where a contractor works for multiple clients simultaneously? Does that automatically point to self-employment?
A5: CEST does not directly ask whether the worker has multiple clients, though that information feeds into the financial risk and business structure sections. Working for multiple clients simultaneously is a strong indicator of genuine self-employment in practice, and it features prominently in HMRC's Employment Status Manual. However, CEST treats each engagement separately. A contractor working for three clients runs CEST three times, once per engagement. An "outside" result for two engagements does not colour the result for the third; each is assessed on its own facts. Where the contractor has genuinely diverse clients, strong financial risk, and operates as a business rather than as an individual embedded in one client's organisation, those facts should flow through into each CEST assessment and support outside results across the board. The practical point is that the multiple-client reality needs to be reflected accurately in each run of the tool, not just noted as a background fact.
Q6: What happens in practice if a medium or large client issues a blanket "inside IR35" determination for all contractors without individual assessments?
A6: This is more common than it should be, and it carries significant legal exposure for the client. HMRC has been clear that blanket determinations , whether inside or outside , do not constitute reasonable care. Reasonable care requires individual assessment of each engagement. Where a client issues a blanket inside determination without proper individual review, the contractor has the right to raise a formal disagreement, to which the client must respond within 45 days. If the client fails to respond, IR35 liability can transfer to the client directly. Beyond the compliance risk, blanket inside determinations are commercially damaging. I have dealt with situations where contractors disengaged and moved to clients with proper assessment processes, simply because the certainty of being taxed as an employee while paying for their own equipment and operating their own company was financially untenable. Clients who blanket-determine inside also lose any protection from HMRC's commitment to stand by CEST results, because CEST was never run.
Q7: Does the 2026 CEST update change how a substitution clause should be drafted or evidenced to support an outside IR35 position?
A7: The update refined the guidance on what constitutes a genuine right of substitution, and it is worth understanding what shifted. The previous guidance was criticised for being over-permissive about what counted as a substitution right. The revised guidance places emphasis on two things: whether the right is unrestricted and genuinely exercisable, and whether it has actually been exercised or is realistically capable of being exercised. Substitution that amounts to recommending a replacement who the client then engages and pays directly , without the original contractor managing or being responsible for that person , may not meet the threshold of a genuine right. The clause in the contract matters, but so does whether it would function in practice. A substitution right that exists only on paper, in an engagement where the client chose the contractor personally and would reject any substitution, carries very little weight. For those drafting or reviewing contracts, the substitution clause needs to be linked to a realistic factual situation where the right could genuinely be invoked.
Q8: Can a contractor challenge their inside IR35 determination through CEST, or is that process only open to the engager?
A8: CEST can be run by either the contractor or the engager, and there is no restriction on who can input the answers. However, where off-payroll rules apply (i.e., the client is medium or large), it is the client's SDS that carries legal weight, not any parallel CEST run by the contractor. The contractor's formal route is the disagreement process: raising a written challenge to the SDS with the end client, who must respond within 45 days setting out whether the determination is maintained or revised, with reasons. If the client fails to respond within 45 days, the liability shifts to them. Running CEST independently as a contractor and getting an "outside" result does not override the client's SDS. It does, however, give the contractor a documented basis for the disagreement, particularly where the client's inside determination relied on a different reading of the facts. The CEST printout is not binding on HMRC in the contractor's hands, but it is evidence of how a reasoned assessment of the same facts came out differently.
Q9: How should a sole trader or self-employed individual use CEST , does it even apply to them?
A9: CEST is primarily built around the off-payroll working rules and the IR35 regime that applies to workers providing services through a limited company (a personal service company). A genuine sole trader providing services directly , with no intermediary company , sits outside IR35 entirely. However, the underlying employment status question still applies to them: are they genuinely self-employed, or are they actually an employee of the client without either party realising it? CEST can give a sole trader a useful indication of where their engagement sits on the employed/self-employed spectrum, even though the legal framework differs. If the tool suggests "employed," that is a signal worth taking seriously, because HMRC can look behind the sole trader label and reclassify the arrangement. For sole traders in trades where long-term single-client relationships are common , certain construction and site-based work comes to mind , running through CEST as a sense check, then seeking a fuller review if the result is borderline, is sensible practice.
Q10: Does the PGMOL Supreme Court ruling mean it is now impossible to argue MOO does not exist in any engagement?
A10: Practically speaking, yes , at least at the basic level. The PGMOL ruling confirmed that the wage-work bargain (agreeing to do work in exchange for pay) is sufficient to establish the minimum threshold of mutual obligation. For almost any commercial engagement where a PSC is paid for services rendered, that minimum will be met. What remains very much arguable , and what PGMOL did not foreclose , is the nature and extent of those obligations. The football referees in that case had narrow, episodic obligations tied to individual matches, with no compulsion to accept future matches and a genuine ability to withdraw even after acceptance. The FTT found those facts to support self-employment. So the argument has shifted from "MOO does not exist" to "the MOO here is narrow and episodic, not the broad and continuous obligation that characterises employment." That is still a meaningful distinction to make, but it requires factual evidence to support it, not just a clause in a contract.
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