Blood pressure is one of the most commonly measured numbers in healthcare, and also one of the least explained. Most people have had it checked at some point — at a GP appointment, a pharmacy, or an NHS Health Check — and walked away with two numbers and not much context for what they actually mean.
What the two numbers are
A blood pressure reading is written as two numbers, such as 120/80, measured in millimetres of mercury (mmHg). The first, higher number is your systolic pressure — the force in your arteries when your heart beats and pushes blood around your body. The second, lower number is your diastolic pressure — the force in your arteries when your heart rests between beats. Both numbers matter, which is why blood pressure is always given as a pair rather than a single figure.
What counts as high, and what counts as normal
According to NHS guidance, you’re generally considered to have high blood pressure if your reading is:
- 140/90 mmHg or higher, when measured by a healthcare professional (a “clinic reading”)
- 135/85 mmHg or higher, when measured at home
That gap between the two thresholds isn’t an inconsistency — it reflects a well-documented pattern where blood pressure tends to read slightly higher in a clinical setting than it does at home, partly due to the stress or unfamiliarity of the appointment itself (sometimes called “white coat” effect). This is exactly why home readings and clinic readings are judged against different cut-offs rather than the same one.
Ideal blood pressure is generally considered to sit below these thresholds, though what’s “normal” for a specific individual can reasonably vary, and a healthcare professional is best placed to interpret a specific reading in the context of your overall health.
Why it’s often called “the silent” risk factor
One of the most important things to understand about high blood pressure is that it usually doesn’t cause any noticeable symptoms. Many people live with elevated blood pressure for years without realising it, which is precisely why routine checks — rather than waiting to feel unwell — matter as much as they do. In rare cases, very high blood pressure can cause symptoms like headaches, blurred vision, or chest pain, but the absence of symptoms is not a reliable sign that blood pressure is fine.
What increases the risk
A number of factors are associated with a higher likelihood of developing high blood pressure, including:
- Increasing age
- A family history of high blood pressure
- Being of Black African, Black Caribbean, or South Asian family background
- A diet high in salt, and low in fruit and vegetables
- Not getting enough physical activity
- Being overweight
- Drinking too much alcohol or caffeine
- Smoking
- Persistently high stress levels
- Poor sleep, including conditions like sleep apnoea
Having one or more of these doesn’t mean high blood pressure is inevitable — it means it’s worth being a bit more proactive about getting checked regularly.
If you’re monitoring at home
Home blood pressure monitors are widely available and can be a genuinely useful way to track readings over time, rather than relying on occasional clinic visits — but accuracy depends on using a properly validated device and following correct technique (sitting quietly for a few minutes beforehand, arm supported at heart height, and taking more than one reading rather than relying on a single number). A GP or pharmacist can advise on a suitable, validated monitor, and can help interpret a series of home readings if you’re asked to track your blood pressure over a period of time rather than relying on a single visit.
When to get it checked, and when to seek help urgently
It’s worth having your blood pressure checked at least every five years if you’re an adult, and more often — closer to annually — if you’re over 40 or have any of the risk factors above. It’s a quick, painless check available at GP practices and many pharmacies, and it’s included as standard in the NHS Health Check for eligible adults.
It’s worth contacting NHS 111 or a GP if you’re experiencing a persistent headache, blurred vision, or unexplained chest discomfort. Call 999 immediately for sudden chest pain accompanied by sweating, nausea, or shortness of breath — these can be signs of a heart attack and need emergency assessment, not a routine appointment.
A number to understand, not to self-diagnose from
It’s worth being clear about the purpose of this kind of explanation: understanding what your numbers mean makes a GP or pharmacist conversation more useful, but a single reading — especially one taken at home, possibly with an unfamiliar device or in a moment of stress — isn’t something to self-diagnose from. If a reading looks high, the right next step is getting it checked properly and discussed with a healthcare professional, not assuming a worst-case scenario or, equally, dismissing it because there are no symptoms.
The practical takeaway
Blood pressure numbers are more straightforward than they’re often made to seem — two figures representing your heart’s effort during and between beats, judged against clearly published NHS thresholds that differ slightly for clinic and home readings. Because high blood pressure usually causes no symptoms, regular checking rather than waiting to feel unwell is the genuinely useful habit here.
