Defined vs Undefined CoS: Which, When & How to Assign

The Certificate of Sponsorship (CoS) is one of the most critical documents when it comes to sponsoring a migrant to work in the UK. It is not a physical paper, but a unique reference number generated on the Sponsorship Management System (SMS).

A common pitfall for new sponsors is confusing Defined and Undefined CoS. Assigning the wrong type can lead to an automatic visa refusal for the applicant and a compliance red flag for your business.

Defined CoS

If you are hiring a migrant who is currently living abroad and applying for their visa from overseas, you must use a Defined CoS. Unlike Undefined CoS, sponsors cannot apply for allocations in advance to keep “stock”. You must apply for a Defined CoS for a specific role and individual via the SMS.

Defined CoS are usually approved within 1 working day, though the Home Office may pause the request to ask for more details about the role to ascertain it is a genuine vacancy.

Once a Defined CoS request is granted. Sponsors will then be able to assign the CoS to that specific individual. 

Undefined CoS

An Undefined CoS is used for migrants who are already in the UK and are switching visas or existing Skilled Workers extending their current permission. 

When you first get your licence, you request a specific number of Undefined CoS which the company needs. This amount can be increased if you need more down the road. 

Undefined CoS can be assigned instantly via SMS. 

If your CoS allocation is empty or you have run out of allocations, you must apply for an increase, which can take up to 18 weeks (or 5 working days via the £350 priority service). However, there is a daily quota for priority service, you can read more on it here.

CoS Pre-Assignment “Checklist”

Once you have determined whether you need a Defined or Undefined CoS, the actual process of assigning it is the final step.Certain errors on the CoS would constitute grounds for an immediate visa refusal without a refund of the sponsorship fee.

1. Personal Details

   
   

It is important to ensure the migrant’s names, date of birth, and nationalities are consistent with their passport details. 

2. Job details and SOC code

   
   

Ensure you are using the correct SOC 2020 classification from the correct Table in Appendix Skilled Occupations. It is important to not choose a SOC code based on the job title alone. Map the actual daily duties to the description in Appendix Skilled Occupations. Most roles must now meet RQF Level 6 (graduate level), though some transitional arrangements exist for those already in the system at RQF Level 3.

3. Work dates and working hours 

   
   

The start date on the CoS cannot be more than 3 months in the future. Exact working hours must be specified on the CoS too. 

4. Salary and Thresholds 

   
   

You must confirm the worker is being paid the higher of both the general salary threshold (usually £41,700 per annum) and the Occupation-specific salary threshold, found in the SOC code tables.

5. Salary tradeable points 

   
   

If you are paying below the standard £41,700 threshold, you must correctly claim tradeable points on the CoS. Some of these include: 

• Migrants under 26, students switching to work visas, or recent graduates are allowed a lower salary (usually £33,400 or 70% of the going rate), but it is time-limited to a maximum of 4 years total (including time spent on a Graduate visa). 

  
  

• If the role requires a PhD, you can claim a lower threshold (£37,500 or 90% of the going rate for relevant PhDs or £33,400 or 80% of the going rate for STEM PhDs). You must provide a credible explanation of why the PhD is relevant to the job.

  
  

• Migrants with jobs that correlate to an SOC code under the Immigration Salary List are also eligible for a lower salary (usually £33,400 AND the going rate)

  
  

Common Error: The Extension Trap

A Skilled Worker is already in the UK and requires a visa extension. The sponsor mistakenly applies for a Defined CoS instead of assigning an Undefined CoS. The request is rejected, the fee is lost, and the delay places the worker’s immigration status at risk.

This is one of the most frequent—and avoidable—CoS errors seen in practice.

Frequently Asked Questions

How long does a Defined CoS take to process?
Short answer: Usually a few working days.

Most requests are decided quickly, but cases requiring additional checks may take longer.

Can a Defined CoS be used for an extension?
Short answer: No.
Extensions and in-country switches always require an Undefined CoS.

What is the cost of assigning a CoS?
The CoS assignment fee applies, and the Immigration Skills Charge is payable where required, depending on sponsor size and visa duration.

How long is a CoS valid?
Once assigned, a CoS is typically valid for three months, during which the visa application must be submitted.

Final Thoughts

Understanding the difference between Defined and Undefined Certificates of Sponsorship is essential for compliant UK visa sponsorship. As enforcement and scrutiny increase, accuracy at the CoS stage has become as important as eligibility itself.

Practical next steps for sponsors:

• Review your annual Undefined CoS allocation
  
  
  

• Audit upcoming hires and extensions by location
  
  
  

• Revise Pre-Assignment checklist before assignment
  
  
  

If you require assistance with complex CoS scenarios or SMS compliance, specialist advice can help reduce risk and ensure continuity of sponsorship.