High Blood Pressure Explained: What Do Your Blood Pressure Numbers Mean?

What is blood pressure?

Blood pressure is the pressure created as blood travels through your arteries.

It is recorded using two numbers.

For example:

128/78 mmHg

The first number is the systolic blood pressure.

The second is the diastolic blood pressure.

What is systolic blood pressure?

Systolic pressure is the higher number.

It represents the pressure in your arteries when the heart contracts and pumps blood around the body.

In:

140/85

the systolic pressure is:

140 mmHg

What is diastolic blood pressure?

Diastolic pressure is the lower number.

It represents arterial pressure while the heart relaxes between beats.

In:

140/85

the diastolic pressure is:

85 mmHg

Both numbers matter.

What counts as high blood pressure in the UK?

Current NICE guidance uses different thresholds depending on where blood pressure is measured.

Clinic measurement

A clinic blood pressure of 140/90 mmHg or higher requires further assessment when hypertension is suspected.

Home or ambulatory monitoring

Hypertension is confirmed when the corresponding average daytime ambulatory or home blood pressure is 135/85 mmHg or higher.^[1]

The threshold is slightly lower outside the clinic because some people's blood pressure rises temporarily when being measured by a healthcare professional.

Why doesn't one high reading diagnose hypertension?

Blood pressure varies naturally throughout the day.

It can temporarily rise because of:

• —stress
• —pain
• —exercise
• —caffeine
• —nicotine
• —illness
• —anxiety
• —poor sleep

Some people also experience the white-coat effect, where blood pressure is higher in a medical environment than at home.

For this reason, NICE recommends ambulatory blood pressure monitoring — or home monitoring if ambulatory monitoring is unsuitable — to confirm many new diagnoses of hypertension.^[1]

What is ambulatory blood pressure monitoring?

ABPM involves wearing a portable blood pressure monitor, usually for around 24 hours.

The device automatically measures your blood pressure repeatedly during normal daily activities and sometimes overnight.

This provides a much broader picture than one reading in a GP surgery.

What is home blood pressure monitoring?

Home blood pressure monitoring allows you to measure your own blood pressure using a validated monitor.

NICE recommends that, when home monitoring is being used to confirm hypertension:^[1]

• —measurements are taken twice daily
• —ideally for 7 days
• —at least 4 days of measurements are obtained
• —the first day's readings are discarded
• —the remaining readings are averaged

Your own healthcare team may provide slightly different practical instructions.

How should I measure my blood pressure at home?

For a reliable measurement:

• —Sit quietly beforehand.
• —Sit with your back supported.
• —Keep your feet flat on the floor.
• —Support your arm.
• —Position the cuff correctly on the upper arm.
• —Remain quiet during the reading.
• —Take a second reading around one minute later.
• —Use a validated upper-arm monitor with the correct cuff size.

NHS England recommends choosing a device validated for accuracy, such as those listed by the British and Irish Hypertension Society.

What is stage 1 hypertension?

NICE defines stage 1 hypertension as:^[1]

• —Clinic: 140/90 to 159/99 mmHg
• —together with:
• —Home/daytime ambulatory average: 135/85 to 149/94 mmHg

Whether medication is recommended depends on factors including cardiovascular risk, diabetes, kidney disease, established cardiovascular disease, evidence of organ damage, age and individual preferences.

What is stage 2 hypertension?

NICE defines stage 2 hypertension as:^[1]

• —Clinic: 160/100 mmHg or higher but below 180/120
• —and:
• —Home/daytime ambulatory average: 150/95 mmHg or higher

Persistent stage 2 hypertension generally requires active management in addition to lifestyle measures.

What is severe hypertension?

A clinic blood pressure of 180/120 mmHg or higher is considered severe hypertension under current NICE guidance.^[1]

This requires prompt clinical assessment.

Importantly, not every reading above 180/120 automatically represents a hypertensive emergency.

NICE recommends same-day specialist assessment when severe hypertension is accompanied by concerning features such as:^[1]

• —new confusion
• —chest pain
• —signs of heart failure
• —acute kidney injury
• —retinal haemorrhage or papilloedema

Does high blood pressure cause symptoms?

Usually not.

This is one reason hypertension is sometimes described as a silent cardiovascular risk factor.

Rarely, very high blood pressure may be associated with symptoms such as:

• —headaches
• —blurred vision
• —chest pain

But feeling completely well does not mean your blood pressure is normal.

Why is high blood pressure harmful?

Persistently raised blood pressure places mechanical stress on blood vessels and organs over many years.

It contributes to:

• —Stroke — hypertension is one of the most important modifiable risk factors for both ischaemic and haemorrhagic stroke.
• —Coronary heart disease — high blood pressure accelerates cardiovascular disease and increases heart-attack risk.
• —Heart failure — the heart may have to work harder against higher arterial pressure. Over time this can contribute to structural changes and heart failure.
• —Kidney disease — the kidneys contain a delicate network of small blood vessels that can be damaged by hypertension.
• —Eye disease — severe or longstanding hypertension can damage the retinal circulation.
• —Vascular dementia — damage to the cerebral circulation over time can contribute to cognitive decline and vascular dementia.

Does lowering blood pressure actually reduce cardiovascular events?

Yes.

The evidence is extensive.

Large individual-participant meta-analyses of randomised trials demonstrate that pharmacological blood-pressure reduction lowers the risk of major cardiovascular events across a wide range of baseline blood pressures and ages.^[3,4]

That does not mean everyone should aim for the lowest possible pressure. The appropriate target depends on the individual.

What blood pressure should someone with hypertension aim for?

For many adults with hypertension aged under 80, current NICE guidance recommends maintaining clinic blood pressure below 140/90 mmHg.

For many people aged 80 and over, the corresponding clinic target is below 150/90 mmHg.^[1]

Different targets can apply in conditions such as:

• —significant chronic kidney disease
• —type 1 diabetes
• —certain cardiovascular conditions

Frailty, falls risk and postural symptoms also matter. Treatment should therefore be individualised.

What can cause hypertension?

For most people there is no single identifiable cause. This is called primary hypertension.

Risk is influenced by factors including:

• —age
• —genetics
• —excess weight
• —high salt intake
• —low physical activity
• —alcohol
• —smoking
• —ethnicity
• —other metabolic risk factors

Can another medical condition cause high blood pressure?

Yes. This is called secondary hypertension.

Potential causes include:

• —kidney disease
• —hormonal disorders
• —obstructive sleep apnoea
• —certain medications
• —adrenal disorders

Secondary causes are particularly considered in selected patients, including some younger adults with hypertension.

NICE advises considering specialist assessment for secondary causes in adults under 40 with hypertension.^[1]

What tests might I have after being diagnosed?

NICE recommends assessment for evidence of organ damage and associated cardiovascular risk.^[1] This may include:

• —kidney-function blood tests
• —electrolytes
• —HbA1c
• —cholesterol
• —urine testing for protein
• —ECG
• —examination of the back of the eyes

Your overall cardiovascular risk should also be assessed.

What lifestyle changes can lower blood pressure?

Reduce excess salt — high dietary sodium can increase blood pressure. Reducing salt intake can help.

Exercise regularly — regular aerobic activity can reduce blood pressure and improve overall cardiovascular health.

Maintain a healthy weight — where relevant, weight loss can meaningfully improve blood pressure.

Limit excessive alcohol — regular heavy alcohol intake can increase blood pressure.

Stop smoking — smoking has major cardiovascular effects even if it does not explain every elevated blood-pressure reading.

Improve the overall diet — dietary patterns rich in vegetables, fruit, whole grains and other minimally processed foods can support cardiovascular health.

Do I still need lifestyle changes if I take tablets?

Yes. Medication and lifestyle changes are complementary, not competing approaches.

Treating hypertension should ideally form part of a broader cardiovascular-prevention strategy.

That includes considering:

• —cholesterol
• —smoking
• —diabetes
• —body weight
• —exercise
• —diet
• —sleep
• —overall cardiovascular risk

What medicines are used?

Several classes of medication can lower blood pressure. Common examples include:

• —ACE inhibitors
• —angiotensin-receptor blockers
• —calcium-channel blockers
• —thiazide-like diuretics

Which medication is recommended depends on factors including age, ethnicity, diabetes, kidney function, other medical conditions, side effects and other medications.

Some people need more than one medication.

Do not start, stop or alter blood-pressure medication without discussing it with the clinician responsible for your care.

Is home monitoring useful after diagnosis?

Yes. Home measurements can help provide a more representative picture of blood pressure outside the clinic.

Recent systematic reviews also support home and ambulatory measurements as valuable predictors of cardiovascular risk.^[5]

Home monitoring works best when it is part of an organised management plan rather than becoming a source of repeated anxiety.

Should I measure my blood pressure 20 times a day?

Usually not.

Blood pressure naturally fluctuates. Repeatedly measuring it because you are worried about individual readings can create more anxiety and make the readings harder to interpret.

Follow a structured schedule agreed with your healthcare professional. The average pattern is usually more useful than one isolated measurement.

The key message

High blood pressure usually does not make you feel unwell — but treating it can substantially reduce future cardiovascular risk.

Know your numbers. Measure them properly. And interpret them alongside your wider cardiovascular health.