A Certificate of Sponsorship (CoS) is a unique digital reference number that a licensed UK employer issues to you for a specific job. It is not a physical document — it's a record created in the Home Office system that confirms your job title, salary, and start date. You need a valid CoS before you can apply for your Skilled Worker visa, and it must be used within three months of being assigned.
The Certificate of Sponsorship confuses almost everyone the first time — mostly because the name makes it sound like a certificate you can hold, frame, or download. It isn't. This plain-English guide explains what a CoS actually is, what's inside it, the difference between the two types, and exactly when and how you get one as part of a UK sponsored job.
A CoS is a reference number, not a document
The single most useful thing to understand: a CoS is a reference number, generated when your employer records the details of your job in the Home Office's Sponsor Management System (SMS). Your employer gives you that reference, and you enter it into your visa application. There's no paper certificate and nothing to carry around — the ‘certificate’ lives entirely as a digital record the Home Office can look up.
What information a CoS contains
When your employer assigns a CoS, they record the specifics of your role. These details must match your visa application and your actual job, so it's worth checking them carefully:
- Your personal details — name, date of birth, nationality, and passport information.
- The job title and its Standard Occupational Classification (SOC) code, which sets the ‘going rate’.
- Your salary, which must meet the relevant threshold for the role.
- The employment start and end dates.
- The sponsor's details and licence information.
- A unique CoS reference number you'll use in your application.
Defined vs undefined CoS
There are two types of Certificate of Sponsorship, and which one you need depends on where you're applying from:
| Type | When it's used | How the employer gets it |
|---|---|---|
| Defined CoS | Skilled Worker applicants applying from outside the UK | Requested from the Home Office for the specific role, usually decided within about one working day |
| Undefined CoS | People already in the UK switching into or extending a Skilled Worker visa (and some other routes) | Assigned from the sponsor's annual allocation of certificates |
When and how you get a CoS
A CoS comes after a job offer, not before. Once an employer decides to sponsor you, they assign the CoS through the Sponsor Management System — for applicants outside the UK, requesting a defined CoS is typically decided within around one working day. You then have three months from the date it's assigned to use it in your visa application, so timing matters: it's usually assigned close to when you're ready to apply, not months in advance.
What to check on your CoS before you apply
Because the details on your CoS must line up with your visa application, check them before you submit and raise anything wrong with your employer straight away:
- Your name, date of birth, and passport number are correct and match your passport exactly.
- The job title and SOC code reflect the role you were actually offered.
- The salary meets the threshold for the role — cross-check it against the current rules.
- The start date and CoS reference number are present and correct.
The salary point is the one most worth double-checking. If the figure on your CoS falls below the required threshold, your application can fail — see our guide to Skilled Worker visa salary thresholds for 2026 to confirm the number for your role.
Where the CoS fits in the bigger picture
The Certificate of Sponsorship is the bridge between getting a sponsored job offer and applying for your visa — the last step before the application itself. It only exists once you've found a licensed employer willing to hire you, which is where most of the effort really goes. For the full journey, see our complete guide to UK visa sponsorship jobs. And to get to a CoS in the first place, create a free Hirely profile — every role we surface is from an employer with an active sponsor licence, so a genuine offer can actually lead to one.