If you sponsor overseas workers, the Certificate of Sponsorship (CoS) is the point where “we’ve made an offer” turns into “we can actually get you a visa”. It’s also where a lot of otherwise solid hires get stuck — not because the role isn’t eligible, but because the CoS type is wrong, the allocation hasn’t been planned, or the details on the certificate don’t line up.
The good news: once you understand how defined and undefined CoS work (and you plan your allocation properly), you can avoid most delays and keep your recruitment moving.
To set the scene with a real-world stat: in the year ending September 2025, the Home Office granted 35,000 Skilled Worker visas to main applicants. Sponsorship isn’t niche — it’s a mainstream hiring tool, and CoS admin is part of the job.
What a CoS actually is (and why it causes delays)
A CoS is an electronic record (not a physical certificate) with a unique reference number. You assign it in the Sponsor Management System (SMS), and the worker uses it to apply for their visa.
A couple of time-sensitive rules matter here:
- Once you assign the CoS, the worker must apply for their visa within 3 months.
- They must not apply more than 3 months before the job start date listed on the CoS.
If those dates don’t work with your onboarding plan, you can accidentally create a delay before the visa application even starts.
Defined vs undefined CoS: the simplest way to remember it
Defined CoS
A defined CoS is for someone applying for a Skilled Worker visa from outside the UK.
You have to apply for a defined CoS through the SMS, then assign it once it’s approved. Applications are usually approved within 1 working day, but can take longer if UKVI needs extra checks.
Typical use case: hiring a candidate who’s overseas and needs entry clearance.
Undefined CoS
An undefined CoS is for:
- Skilled Workers applying from inside the UK, and
- all other sponsored routes (for example Global Business Mobility categories, and many Temporary Worker routes).
Undefined CoS are tied to your allocation planning: when you apply for your sponsor licence, you estimate how many undefined CoS you’ll need in year 1.
Typical use case: switching someone already in the UK into Skilled Worker, extending a Skilled Worker, or sponsoring on other routes.
Allocation planning: how to stop CoS becoming a bottleneck
If you only plan CoS once you’ve found “the perfect candidate”, you’re doing it the hard way.
1) Build a simple 12-month hiring forecast
You don’t need a spreadsheet masterpiece. Just answer:
- How many hires are likely from outside the UK (defined CoS)?
- How many hires or extensions are likely inside the UK (undefined CoS)?
- Any seasonal spikes (graduate intake, project ramp-ups, contract wins)?
This matters because defined CoS are requested per person, whereas undefined CoS depend on what’s left in your annual allocation.
2) Watch out for business changes that affect your CoS needs
New contract? New site? Acquisition? You can go from “2 hires a year” to “15 hires in 6 months” very quickly. If you want a deeper dive on the compliance side of business change, read Sponsor Licence Compliance.
3) Special case: UK Expansion Worker (provisional rating limits)
If you’re sponsoring a UK Expansion Worker and you have a provisional rating, you can only assign 1 CoS (usually to your Authorising Officer) so they can enter the UK. After they have their visa, you can upgrade to an A-rating and request up to 9 additional CoS via SMS.
If you don’t plan for that limitation, it can derail a whole market-entry timeline. For the route itself, see UK Expansion Worker Visa.
Fees and budgeting: what you need to know upfront
Costs don’t just matter for finance — they affect how quickly you can assign the CoS (for example, if payment approvals are slow internally).
CoS fee (payable when you assign)
- Worker CoS: £525 per certificate
- Temporary Worker CoS: £55 per certificate
You must pay these costs as the sponsor. Asking the worker to pay can put your licence at risk.
Immigration Skills Charge (ISC) — often forgotten
If you assign a CoS for someone applying for a Skilled Worker (or Senior or Specialist Worker) visa, you may also need to pay the Immigration Skills Charge.
As a rough guide:
- Small/charitable sponsors: £480 for the first 12 months, then £240 per additional 6 months
- Medium/large sponsors: £1,320 for the first 12 months, then £660 per additional 6 months
Again, you must pay it yourself — the Home Office is clear that passing costs to the worker can lead to licence action.
If you’re trying to price the “true cost to hire”, the CoS fee + ISC are usually the numbers that surprise people.
Avoiding delays: the top CoS mistakes (and how you dodge them)
1) Picking the wrong CoS type
If the candidate is outside the UK and applying for Skilled Worker entry clearance, you need a defined CoS.
If they’re inside the UK (switching/extending) it’s undefined.
Sounds obvious — but it’s one of the most common reasons sponsors end up stuck in admin loops.
2) Getting the job details “almost right”
CoS errors that often trigger delays or refusals include:
- wrong occupation code for the role
- salary figures that don’t align with the route requirements
- start dates that don’t match the candidate’s realistic notice period or visa timeline
- work location not reflecting reality (especially where hybrid working is involved)
If you’re sponsoring under Skilled Worker and want a clean overview of the route, see Skilled Worker Visa.
3) Leaving the CoS until the end of the hiring process
If you know the role is a sponsorship role, start your checks early:
- confirm job description and level
- sanity-check salary budget
- identify whether the candidate will apply from inside or outside the UK
- map a realistic start date that respects the “3-month” rule on visa application timing.
4) Underestimating allocation needs for in-country switching
If you regularly hire international graduates switching from Student, or you extend existing Skilled Workers, your undefined allocation needs can be bigger than you expect — especially as teams grow.
5) Poor internal approvals for paying fees
This sounds boring, but it’s real. If your finance approvals take 2 weeks, your “1 working day” defined CoS approval timeline won’t save you.
Build a fast-track internal process for CoS and ISC payments.
When to get help
If your CoS workflow is regularly causing delays, it usually means one of 3 things:
- your allocation planning is off
- your role details aren’t being mapped cleanly to sponsorship requirements
- your internal process (SMS access, approvals, evidence) is too slow
That’s exactly the sort of issue a structured review can fix — before it turns into a compliance problem. If you want a broader sponsor-lifecycle view, Sponsor Licence Applications is a useful starting point, and if you’re worried about Home Office action, read Sponsor Licence Suspension and Revocation.
Next steps
If you want your sponsorship process to feel predictable (rather than a last-minute scramble), the CoS system is where you win or lose time.
If you’re not sure whether you need defined or undefined CoS, you’re running low on allocation, or you’ve had delays that are pushing start dates back, speak to Garth Coates. Use the Contact page to request a consultation, and you’ll get a clear plan for CoS allocation, assignment, and timing — so your hires can start work when you actually need them to.
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