What Is a CAS Number for a UK Student Visa? (2026)

A CAS number is one of the most misunderstood parts of the UK Student visa process, partly because applicants assume it's a physical certificate similar to a US I-20, and partly because a genuine, expected wait for one often gets mistaken for a problem. Here's what it actually is, what it contains, and the timing that trips up more applicants than the document itself does.

What a CAS actually is

Confirmation of Acceptance for Studies (CAS) is an electronic record, not a physical or even a standalone PDF document in the way an I-20 is. Your sponsoring university, licensed by the Home Office as a Student visa sponsor, creates this record in its own system and gives you a unique 14-character reference number along with the underlying details, your course, its dates, your tuition fee and any deposit already paid, and your own biographical information. When you complete your online Student visa application, you enter that reference number, and the Home Office pulls the associated record directly rather than you attaching a document yourself.

Unconditional offers only

Universities generally won't issue a CAS against a conditional offer, one where you still need to meet an academic requirement (a final grade, a language test) or a financial one (a tuition deposit) before your place is confirmed. The practical sequence is: clear every condition attached to your offer first, have the university convert it to unconditional, and only then request or wait for your CAS. Trying to apply for a visa, or even asking your university to hurry a CAS along, while your offer is still conditional isn't something a CAS process can shortcut, the unconditional step has to happen first regardless of how close a deadline is.

Who actually issues it, and who doesn't

Only a university or college holding an active Student visa sponsor license from the Home Office can issue a CAS at all, this is a formal status, not something every UK educational institution automatically has. If an institution loses its sponsor license, current and prospective students can be left needing to transfer to a licensed institution to continue their studies under the Student visa route, which is a real though relatively rare risk worth being aware of when evaluating a lesser-known or newer institution. Most established universities have held their sponsor license for years without incident, but checking a specific institution's current sponsor status on the Home Office's published register before committing is a reasonable, low-effort precaution.

Why the timing window trips people up

A Student visa application can't be submitted more than a fixed window before your course actually starts, and universities calibrate their CAS issuance to that same window rather than to how eager an individual applicant is. Common practice is roughly 6 months before your start date if you're applying for your visa from outside the UK, or roughly 3 months before if you're applying from inside the UK. If you have a confirmed unconditional offer well ahead of that window and no CAS yet, that's normal, not a sign something has gone wrong with your file, the university is simply waiting for the point at which issuing one actually becomes useful to you. Once you're inside the relevant window, most universities issue a CAS within roughly 5 to 20 working days of your offer going unconditional and, where required, your deposit clearing.

The six-month clock, and why you shouldn't request one too early

Once issued, a CAS is valid for six months and can be used for exactly one Student visa application. If your visa is refused for any reason, or your course dates or funding details change enough that the university needs to reissue it, you'll need a fresh CAS, the original number simply stops being usable. Because of this, there's little upside to pushing for an unusually early CAS even if your university would technically allow it, you're better off timing the request so the six-month validity window comfortably covers your actual visa application and, ideally, your planned travel date, rather than requesting the earliest possible number and risking it expiring before you've applied.

Only one sponsor, one CAS: what happens if you switch universities

A CAS is issued by a single sponsoring institution and tied specifically to that institution's course. If you hold offers from more than one UK university and later decide to switch, your original university's CAS becomes irrelevant to the new one, the new institution has to issue its own CAS once your offer there is unconditional, following the same sequence and timing rules described above from scratch. This also applies if you're already holding a valid visa from an earlier CAS and change institutions before starting, a change of sponsor generally requires a fresh visa application built around the new CAS, not simply notifying your new university of an existing visa. If you're weighing multiple UK offers, factor this into your decision timeline, switching late enough that a new CAS and visa application can't realistically complete before your intended start date is a genuine, avoidable risk worth planning around.

What your CAS actually confirms about your finances and your English

Beyond your course details, a CAS carries two pieces of information that directly shape the rest of your visa application. It states the tuition and, where relevant, living-cost figures your university has confirmed, the exact numbers your financial evidence needs to demonstrate you can cover, on top of whatever you've already paid as a deposit. It also states whether you need to submit a Secure English Language Test result, or whether your university's own assessment already satisfies the Home Office on your behalf. That second field is worth reading closely before you assume you need to sit IELTS or a similar test at all, our guide to proving English proficiency without IELTS or TOEFL covers the general mechanics of this kind of institutional waiver, and how UK-specific rules for a funded PhD applicant work in more depth than fits here.

What happens if you change course or defer after your CAS is issued

A CAS is tied to specific details, your course, its start and end dates, and the fee figure agreed at the point of issuance, so a meaningful change after the fact generally requires a new one rather than an amendment to the existing record. If you defer your start date to a later intake, change programs, or your university revises your fee or funding details, your university typically has to withdraw the original CAS and issue a replacement once the new details are confirmed, and that replacement carries its own fresh six-month validity window rather than inheriting whatever remained on the original. If you're weighing a deferral, it's worth asking your university directly whether that will trigger a CAS reissue and, if so, roughly how long the replacement typically takes, rather than assuming your existing number will simply carry over unchanged.

How the CAS figures connect to what you actually need to show in savings

The tuition and living-cost figures on your CAS aren't just informational, they're the exact numbers your financial evidence for the visa application is measured against, alongside the UK's specific 28-day holding-period rule for that evidence. A CAS that states a lower-than-expected fee because a deposit has already been paid, or a higher figure because it includes a full year's living costs rather than a partial term, directly changes the amount you need to demonstrate, so read these figures carefully rather than estimating your own financial requirement independently of what your specific CAS actually states.

A CAS shortage number, and what that means

Occasionally you'll see the term "CAS shortage number," which refers to a small number of specific occupation categories where a slightly different reference is issued for related visa routes, not the standard Student visa CAS most applicants encounter. If your own paperwork or university correspondence uses this exact term, check with your specific institution's international office directly rather than assuming it applies to a standard degree-level Student visa application, it usually doesn't, and the terminology gets applied loosely in some third-party guides in a way that causes unnecessary confusion.

CAS versus the older Tier 4 terminology you might still see

Some older guides and forum threads still refer to a "Tier 4 CAS" or the Tier 4 visa route generally, the UK's points-based immigration system that the Student visa route replaced in 2020. The underlying CAS mechanism carried over largely intact into the current Student visa route, so most of what an older Tier 4 guide describes about how a CAS works still holds true today, but names, some specific figures, and a few procedural details have changed since. If you come across a Tier 4-labeled resource while researching this, treat the general mechanics as broadly still applicable while checking gov.uk's current Student visa guidance directly for anything specific and numerical, minimum funds, current fees, or exact document lists, rather than trusting an older figure that predates the 2020 change.

Multi-year PhDs and how CAS renewal actually works

Unlike a one-year taught master's, a PhD commonly runs three to four years or longer, and your initial Student visa is generally granted for a period tied to your current CAS rather than automatically covering your entire expected programme length. In practice, most PhD students apply for their visa covering the confirmed portion of their study, then extend, with a new CAS issued by their university, if their programme genuinely runs longer than originally granted for. This is a normal part of a multi-year doctoral timeline rather than a sign of a problem, but it does mean tracking your visa's actual expiry date against your real, sometimes-extended PhD timeline is your own responsibility, not something that happens automatically in the background.

If something on your CAS looks wrong

Because a CAS is generated from data your university holds on file, a wrong course date, a misspelled name, or an incorrect fee figure usually traces back to something in your own application or offer record rather than an error introduced at the CAS stage itself. Contact your university's international student or admissions office directly to have it corrected and reissued rather than submitting a visa application against a CAS you already know contains an error, a mismatch between your CAS and your passport or other application details is a real, avoidable reason for delay or refusal.

None of this paperwork mechanics matters until you actually have an offer to build a CAS around, and for many PhD applicants that offer starts with a specific supervisor agreeing to take you on. GradScoutFunding searches professors by field and country, confirms they're actively publishing, and drafts a personalized first email grounded in a real recent paper of theirs for you to review and send yourself. Get 2 free credits, no card required.

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