Confused about fit notes? Discover when they’re required, what they contain, and how they help employees return to work safely.
Medically reviewed by Dr Sulaiman Shah , MBChB BMedSci, MRCGP — General Practitioner and founder of The GP Clinic.Last reviewed: 16 September 2026
Most people read a medical certificate exactly once — the day they need it — and half the wording on it doesn’t mean much. “Prognosis guarded.” “Diagnosis: unspecified viral illness.” A duration that’s clearly an estimate but doesn’t say so anywhere obvious.
This guide goes through every section of a UK medical certificate or fit note in plain English, so you know exactly what you’re looking at and what your employer, school, or insurer is actually being told.
| Section | What it actually tells the reader |
|---|---|
| Patient details | Confirms who the certificate belongs to — name, date of birth, sometimes address |
| Assessment date | When the clinician actually saw or spoke to you — not necessarily the date the document was printed |
| Diagnosis | The medical reason for your absence, sometimes deliberately non-specific |
| Prognosis | The clinician’s expectation for how and when you’ll recover |
| Recommendations / restrictions | What you should or shouldn’t do while unwell |
| Duration | The estimated period you need off, or the period already covered |
| Signature, stamp, registration number | What makes the certificate valid and checkable |
This section confirms the certificate belongs to you: full name, date of birth, and sometimes an address. It exists so an employer or institution can be confident the document matches the person presenting it — a certificate with no name or an obvious mismatch isn’t valid evidence of anything.
The assessment date is when a clinician actually examined you or spoke with you — in person, by phone, or by video call. The issue date is when the document itself was produced. These aren’t always the same day. A certificate can also cover a period that started before the assessment, if the clinician judges that your fitness for work was already affected at that point.
If the dates on your certificate look mismatched, that isn’t automatically an error — check whether it’s an assessment date or an issue date before assuming something’s wrong.
The diagnosis section names the medical reason for your absence. Official DWP guidance for fit notes states that clinicians should be as accurate as possible, but are permitted to use a less precise description where a detailed diagnosis could disadvantage the patient with their employer — for example, writing “stress-related illness” rather than naming a specific mental health condition. This isn’t the clinician being vague for no reason; it’s a deliberate privacy protection built into the system.
A few terms that commonly cause confusion:
You are never entitled to more diagnostic detail than the certificate provides, and your employer isn’t entitled to ask you for it directly — the certificate itself is the extent of what they can require.
Prognosis is the clinician’s expectation of how your recovery is likely to go. It’s often summarised in a short phrase:
None of these are a guarantee — a prognosis is a clinical judgement based on the information available at the time, not a fixed outcome.
This is where the certificate tells you, and your employer, what you should or shouldn’t be doing. On a UK fit note specifically, this section can go beyond a simple yes/no by ticking one of several boxes: a phased return to work, amended duties, altered hours, or workplace adaptations. This “may be fit for work” option, introduced when the fit note replaced the old-style sick note in 2010, means a certificate doesn’t have to be all-or-nothing — it can describe exactly what would let you keep working safely.
The duration section states how long you’re expected to need off, or the period already covered. It’s worth remembering this figure is a clinical estimate based on typical recovery patterns for your condition, not a fixed deadline. If you recover faster or slower than expected, that’s normal — you’d typically be reassessed rather than treated as bound by the original date.
A certificate isn’t valid without the issuing clinician’s signature and, for medical certificates specifically, their professional registration number (for a GP, their GMC number). This is what allows an employer to verify — if they ever need to — that the person who issued it is a real, currently registered healthcare professional. A certificate missing this information shouldn’t be accepted, since there’s no way to confirm it’s genuine.
Not quite. In the UK, a fit note (Statement of Fitness for Work, form Med3) is specifically the document used for work absence beyond seven days and for Statutory Sick Pay purposes. It can only be issued by an authorised healthcare professional following an assessment. A medical certificate is a broader term — it might be a private doctor’s letter confirming a diagnosis for insurance, travel, or an educational institution, and doesn’t follow the exact same format as a fit note. Employers generally accept either for day-to-day sickness absence, but only an NHS fit note is accepted as evidence for state benefits like Employment and Support Allowance or Universal Credit.
Ask. You’re entitled to ask the issuing clinician to explain any wording you don’t follow — the certificate is about your health, and understanding it is part of good care. If you’ve lost the certificate or need a copy, contact the issuing GP practice or provider directly rather than trying to recreate it yourself.
A medical certificate isn’t written to be cryptic — most of its wording follows a standard structure once you know what to look for. Patient details confirm who it belongs to, the assessment date tells you when you were seen, the diagnosis and prognosis explain what’s wrong and what to expect, the recommendations section says what you should do about it, and the signature confirms it’s genuine. If anything on your own certificate still doesn’t make sense, the person who issued it is the right person to ask.
It means the clinician sees genuine uncertainty about how your recovery will go — not that anything is necessarily wrong, but that the outcome depends on factors that aren’t yet clear. It’s a standard clinical term, not a cause for alarm on its own.
No. The certificate provides exactly the level of detail your employer is entitled to. If the diagnosis is written non-specifically, your employer cannot require you to explain it further — your specific medical information remains private.
Clinicians can backdate a fit note if they judge, based on your assessment, that your fitness for work was already affected before that appointment. The assessment date and the start of the covered period aren’t required to match.
Not legally. Both are usually accepted by employers for everyday sickness absence, but only an NHS fit note (Med3) from a registered GP is accepted as evidence for state benefit claims such as Employment and Support Allowance or Universal Credit.
Deliberately obtaining or issuing a false medical certificate is a serious matter that can amount to fraud, with consequences for both the person who submitted it and, if a clinician was knowingly involved, their professional registration. Certificates exist precisely because employers and institutions rely on them being accurate.
