Blood Pressure Explained: What Normal, High and Low Readings Mean  

High blood pressure often has no symptoms. Because you can’t feel it, it’s sometimes called the ‘silent killer’. Yet it affects more than one in four adults in the UK, increasing their risk of serious health problems like heart attacks and strokes if left untreated.

With the rise of home blood pressure monitors, more of us are seeing our numbers day-to-day. But seeing a reading of ‘135/85 mmHg’ on a screen can be confusing. Is it good? Is it bad? What should you do next? As a GP, I’ve had thousands of conversations helping patients make sense of these numbers, and this guide is designed to give you that same clarity.

This comprehensive guide is for anyone who wants to understand their blood pressure readings—whether they're normal, high, or low. This article is for general information and does not replace advice from a qualified clinician. It is a tool to help you have more informed conversations with your GP. You will learn what blood pressure is, how to interpret the different categories of readings, what to do for each level, how to measure your pressure accurately, and when to seek medical advice.

Understanding Blood Pressure Numbers

Blood pressure is the force exerted by your circulating blood on the walls of your arteries, the vessels that carry blood from your heart to the rest of your body. Your blood pressure reading provides a vital snapshot of how hard your heart is working and the health of your arterial system.

What is Blood Pressure?

At its most basic, blood pressure is the pressure of your blood pushing against the walls of your arteries as your heart pumps it around your body. Think of it like water pressure in a garden hose. When you turn the tap on, water flows through the hose under pressure. Your heart is the tap, and your arteries are the hose. A healthy level of pressure is essential to ensure that oxygen and nutrients are efficiently circulated to all your vital organs and tissues.

Systolic Pressure (Top Number)

Your blood pressure reading is given as two numbers, and the first, or top, number is your systolic blood pressure. This is the highest level your pressure reaches when your heart muscle contracts (beats) to pump blood out into your arteries. This number indicates the maximum pressure your arteries experience during a heartbeat.

Diastolic Pressure (Bottom Number)

The second, or bottom, number is your diastolic blood pressure. This is the lowest level your pressure falls to as your heart muscle relaxes between beats, allowing it to refill with blood. This number represents the amount of pressure in your arteries when your heart is at rest. The measurement is recorded in 'millimetres of mercury', which is why you see it written as mmHg.

Which number is more important?

Both numbers are important for assessing your cardiovascular health. While diastolic pressure was once considered more significant, we now know both are crucial. For people over 50, the systolic (top) number is often a more important risk factor for heart disease or stroke. Your clinician will always look at both numbers together, in the context of your overall health, to make an accurate assessment.

Blood Pressure Categories and Actions

Your blood pressure reading falls into one of several categories, each with its own recommended course of action. These categories are a guide to help you and your doctor understand your reading and decide on the next steps. It's important to remember that a single high reading does not necessarily mean you have high blood pressure (hypertension); your GP will look for a sustained pattern of high readings over time before making a diagnosis.

The table below outlines the five main categories used to classify adult blood pressure readings.

Normal blood pressure (less than 120/80 mmHg)

A normal reading indicates that your heart and arteries are not under excessive strain. This is associated with a lower risk of heart disease and stroke. Actionable advice: To maintain this healthy reading, continue with a balanced diet, regular physical activity, and moderate alcohol intake. We recommend you get your blood pressure checked every five years, or more frequently if advised by your GP.

Elevated blood pressure (120–129 / less than 80 mmHg)

This category serves as a warning. While not technically high blood pressure, your levels are higher than ideal and are likely to worsen over time without intervention. Actionable advice: This is the best time to take proactive steps to prevent hypertension.

1. Reduce salt: Aim for less than 6g (one teaspoon) of salt per day.
2. Increase activity: Aim for at least 150 minutes of moderate-intensity exercise, like brisk walking or cycling, each week.
3. Monitor: Check your reading at home occasionally and book a routine GP appointment to discuss your results.

High blood pressure stage 1 (140/90–159/99 mmHg)

At this stage, a formal diagnosis of hypertension may be considered, especially if your readings are consistently in this range. Your GP will assess your overall cardiovascular risk to decide on the best course of action. Actionable advice: Book an appointment with your GP. They will likely recommend significant lifestyle changes and may consider starting medication. Prepare for your appointment by thinking about:

• Questions to ask your doctor: How often should I monitor my pressure at home? What are the most important lifestyle changes for me? Based on my other health factors, am I a candidate for medication now?

High blood pressure stage 2 (160/100–179/119)*

Readings consistently in this range mean that treatment is almost always recommended to reduce your risk of serious health problems. Actionable advice: It is very important to see a GP. The management plan will typically involve a combination of prescribed medication and structured advice on diet and exercise. Following your doctor's treatment plan is crucial to control your blood pressure and protect your long-term health.

Hypertensive crisis (higher than 180/120 mmHg)

A reading this high indicates a severe elevation in blood pressure that can damage your organs. Your immediate actions depend on whether you have symptoms.

• If your reading is this high but you feel fine (no symptoms): Don't panic. Wait five minutes and measure it again. If it remains this high, contact your GP surgery for an urgent same-day appointment. If your surgery is closed, call NHS 111 for advice.
• If your reading is this high AND you have symptoms: Chest pain, shortness of breath, back pain, numbness, weakness, a change in your vision, or difficulty speaking are signs of a medical emergency. Call 999 for an ambulance immediately.

Low Blood Pressure (Hypotension)

Low blood pressure, known clinically as hypotension, is a reading of 90/60 mmHg or lower, which is often normal but becomes a medical issue when it causes symptoms. While much of the focus is on high blood pressure, it's also important to understand low blood pressure, as for some it can signal an underlying problem.

What is considered low blood pressure?

Low blood pressure is generally defined as a reading of 90/60 mmHg or lower. For many active, healthy people, readings in this range are perfectly normal and can be a sign of a very healthy cardiovascular system. Hypotension only becomes a medical issue when it causes noticeable symptoms, which happens when the pressure is too low to deliver enough oxygenated blood to the brain and other organs.

Symptoms of Low Blood Pressure

If your blood pressure drops too low, you might experience symptoms such as:

• Dizziness or light-headedness, especially when standing up
• Fainting (the medical term is syncope)
• Blurred or distorted vision
• Nausea
• Unusual fatigue or weakness
• Lack of concentration

Causes of Low Blood Pressure

A blood pressure reading can be low for many reasons, ranging from everyday factors to more serious medical conditions.

• Everyday factors: Dehydration is a common cause, as is standing up too quickly after sitting or lying down (this is called postural hypotension). Your blood pressure also naturally fluctuates and is often lowest at night.
• Medications: Some medicines can lower blood pressure as a side effect, including certain diuretics ('water pills'), beta-blockers used for heart conditions, and some types of antidepressants.
• Underlying health conditions: Pregnancy often causes a temporary drop in blood pressure. Other potential causes include heart problems, endocrine issues (like thyroid disease), severe infections (sepsis), or significant blood loss.

When to See a Doctor for Hypotension

It’s important to consult a GP if you have consistently low blood pressure readings accompanied by any of the symptoms listed above. We can help investigate the cause, which might involve reviewing your medications or running some simple tests. A single low reading without symptoms is usually nothing to worry about, but if you're feeling unwell, it's always best to get checked.

How to Measure Blood Pressure at Home

Accurate home blood pressure monitoring requires following a consistent and correct technique to ensure readings are reliable. Inaccurate measurements can lead to unnecessary anxiety or, conversely, a false sense of security, so following a proper routine is key to getting a reliable reading.

Step-by-Step Measurement Guide

For the most reliable results, follow this simple routine every time you measure your blood pressure.

1. Prepare: For 30 minutes before you measure, avoid caffeine, alcohol, smoking, and exercise, as these can all temporarily raise your blood pressure. Make sure your bladder is empty. Sit down in a quiet place and rest for at least five minutes.
2. Position yourself correctly: Sit upright in a dining chair with your back straight and supported. Your feet should be flat on the floor—do not cross your legs. Rest your arm on a table or cushion so that your upper arm is level with your heart.
3. Place the cuff: The cuff should be placed on your bare upper arm (not over clothing). The bottom edge of the cuff should be about one inch above the bend of your elbow. It needs to be snug enough that you can only slip two fingers underneath it.
4. Take the reading: Press the start button. It's important to remain still and silent while the machine is working. Don't talk or look at your phone.
5. Record the result: We advise taking two or three readings, each about one minute apart, and calculating the average. Keep a log of your results, including the date and time of each measurement. It is good to do this in the morning and evening and keep a 2 week dairy.

Common Measurement Mistakes

A surprising number of things can artificially raise or lower your reading. Avoid these common errors:

• Measuring over clothes: This can add several points to your reading.
• Using the wrong size cuff: A cuff that is too small for your arm can significantly overestimate your blood pressure. Most monitors come with a medium cuff, but larger or smaller sizes are available.
• Having a full bladder: This can temporarily increase your systolic pressure.
• Talking or moving: This can affect the machine's ability to get an accurate measurement.
• An unsupported arm: If your arm is hanging down or you're holding it up, your muscles are tensed, which can alter the reading.

Risk Factors and Special Considerations

Certain factors increase the risk of developing high blood pressure, meaning some people need to pay special attention to their readings. Understanding these risks helps you and your doctor take a more proactive approach to your health.

Age

As we age, our arteries naturally tend to become stiffer, leading to a condition called arteriosclerosis. This forces the heart to pump harder, often causing a rise in systolic (top number) pressure. This condition, known as isolated systolic hypertension, is very common in people over 60 and requires management just like other forms of high blood pressure. Regular monitoring is therefore particularly important in later life.

Pregnancy

Blood pressure is monitored closely throughout pregnancy as part of routine antenatal care. Some people develop high blood pressure for the first time during pregnancy (gestational hypertension), which requires careful management to protect both parent and baby. It is also a key sign of pre-eclampsia, a more serious condition that can affect the placenta and the parent's organs.

Ethnicity

Your ethnic background can influence your risk. In the UK, people of Black African or Black Caribbean descent are more likely to develop high blood pressure, and often at a younger age, than the general population. Because of this higher risk, it is often recommended that blood pressure checks begin earlier and are carried out more frequently.

Co-existing Health Conditions

Having certain long-term health conditions makes it even more important to control your blood pressure.

• Diabetes: High blood glucose can damage arteries, making them more prone to hardening. The combination of diabetes and high blood pressure significantly increases the risk of heart disease, stroke, and kidney disease.
• Kidney disease: The kidneys and circulatory system are closely linked. Chronic kidney disease can cause high blood pressure, and high blood pressure is a leading cause of chronic kidney disease. Careful blood pressure management is essential to protect kidney function.

If you have diabetes or kidney disease, a clinician at Doctor Care Anywhere can help you create a plan to manage your blood pressure effectively.

Conclusion

Understanding your blood pressure is a fundamental step towards taking control of your cardiovascular health. By now, you should feel more confident about what your systolic and diastolic numbers mean, the clear next steps associated with each blood pressure category, and how to measure your readings accurately at home.

Regularly monitoring your blood pressure is one of the most powerful and proactive things you can do for your long-term wellbeing. The numbers on the screen are not a judgement; they are a tool. Use them to understand your body better and to have more informed, confident conversations with your healthcare provider about how to protect your health.

If you are concerned about a reading, have symptoms of low blood pressure, or want to create a personalised plan to manage your health, our GPs are here to help. Book an appointment with a Doctor Care Anywhere GP today.

 * Stage 2 hypertension - Clinic blood pressure of 160/100 mmHg or higher but less than 180/120 mmHg and subsequent ABPM daytime average or HBPM average blood pressure of 150/95 mmHg or higher