The cuff tightens around your arm, the machine starts humming and you sit there trying very hard to relax. Then the doctor reads out two numbers that are higher than you expected, and relaxing suddenly gets a lot harder.
The first time that happened to me, I wanted to know what those two numbers actually meant, and whether a reading taken while I was sitting nervously in a clinic really reflected my normal blood pressure. It turns out there is a good reason to ask. Blood pressure changes throughout the day, rising with exercise, stress or pain and falling when you rest, and plenty of people find it runs higher at the doctor’s surgery than it does at home.
So what is high blood pressure, what causes it, and how do you know whether a reading is something to worry about? Along the way, I also found out that Australia and the United States do not even agree on where “high” begins.
What is blood pressure?
Every time your heart beats, it pushes blood into your arteries, and as that blood travels around your body it presses against the artery walls. That pressure is your blood pressure. A reading is written as two numbers, such as 120/80 mmHg, measured in millimetres of mercury, a unit left over from the original mercury-filled instruments.
The first number is your systolic pressure, the pressure in your arteries when your heart contracts and pumps blood. The second is your diastolic pressure, the pressure while your heart relaxes between beats. The instrument that measures them has a wonderfully unwieldy name, the sphygmomanometer, although most people just call it a blood pressure monitor. Modern ones use an inflatable cuff around the upper arm and an electronic sensor.
Blood pressure is not a fixed number. It changes with what your body is doing and can be affected by stress, activity and your general health. It also follows a daily pattern as part of your circadian rhythm, generally dropping while you sleep and rising as you become active. That is why one reading on its own rarely tells the whole story.
What is considered high blood pressure in Australia?
In Australia, high blood pressure, or hypertension, is generally defined as a reading of 140/90 mmHg or higher. That means your systolic pressure is 140 or above, your diastolic pressure is 90 or above, or both. The Heart Foundation’s guideline also recognises some lower categories:
| Blood pressure (mmHg) | Australian category |
|---|---|
| Less than 120/80 | Optimal |
| 120-129 / 80-84 | Normal |
| 130-139 / 85-89 | High-normal |
| 140/90 or higher | High blood pressure |
These numbers are a general guide. Your doctor will interpret your readings in the context of your age, medical history and overall risk of heart disease and stroke. A single high reading also does not automatically mean you have hypertension, which is why Healthdirect describes it as readings that are consistently above 140/90, and why repeated measurements are usually needed to confirm it.
Why does the US use 130/80?
This is one of the more confusing things about blood pressure, and it was the part that surprised me most. Search online and you may find an American chart saying 130/80 is already hypertension, while an Australian source says high blood pressure starts at 140/90. Both are correct, because they follow different clinical guidelines.
The 2025 American Heart Association and American College of Cardiology guideline classes a top number of 130-139 or a bottom number of 80-89 as stage 1 hypertension, and anything from 140/90 up as stage 2. It also weighs a person’s overall cardiovascular risk when deciding whether to start medication. Australia uses the 140/90 threshold, with cardiovascular risk and other factors also considered when deciding how someone should be managed.
So a reading of 135/85 would be “high-normal” to an Australian GP and “stage 1 hypertension” to an American one. It is a good reminder that medical definitions are decisions made by experts weighing the evidence, not lines drawn by nature, and it is worth checking where an online blood pressure chart comes from before comparing it with what your GP tells you.
Why is your blood pressure higher at the doctor’s?
If your readings are normal at home but consistently higher when you visit the doctor, there is a name for it: white coat hypertension. It describes blood pressure that is raised in a medical setting but lower when measured anywhere else. Healthdirect explains that it is common to feel stressed or anxious when a health professional takes your blood pressure, and because stress pushes blood pressure up, a clinic reading can be higher than your real, everyday figure. A 2025 review in the journal Cureus puts it at around one in five people whose clinic readings come back high.
Nerves are not the only thing that can inflate a reading. Your blood pressure may be temporarily higher if you have recently exercised, rushed to get to your appointment, had caffeine or a cigarette, or are in pain or stressed. Talking during the measurement, not sitting quietly beforehand and even having a full bladder can all nudge the numbers up as well.
It is tempting to write white coat hypertension off as “just nerves”, but researchers are not convinced it is completely harmless. One long-running study summarised by the European Society of Cardiology followed people with white coat hypertension for ten years and found that 43% had gone on to develop sustained high blood pressure.
This is one reason your doctor may ask you to monitor your blood pressure at home, which gives a much better picture of what it is doing during a normal day. Healthdirect says doctors often ask for readings twice a day, morning and evening, for seven days. Some people are also asked to wear a 24-hour ambulatory blood pressure monitor, which records readings through the day and night while you go about your usual routine. So if your numbers always seem higher at the GP, don’t just assume the machine is wrong. Tell your doctor what you are seeing at home, because comparing readings from different settings is exactly how they work out what is really going on.
Why does high blood pressure matter?
One of the tricky things about hypertension is that you usually cannot feel it. Most people with high blood pressure have no obvious symptoms, so there is no reliable way to tell whether yours is elevated just by how you feel. Over time, though, consistently high pressure puts extra strain on the heart and blood vessels, and Healthdirect lists it as a major risk factor for heart disease, heart attack, stroke, heart failure and chronic kidney disease.
It is also far more common than most of us assume. The Australian Institute of Health and Welfare estimates that 39% of Australian adults had hypertension in 2022, or roughly 7.2 million people. Even more striking, 63% of those adults did not report having the condition, which suggests many of them simply did not know.
What causes high blood pressure?
There usually is not one simple cause. For most people, hypertension develops gradually as age, genetics, lifestyle and other health factors combine over the years. Some of those factors cannot be changed: getting older and having a family history of high blood pressure both increase your risk. Others can be, including carrying extra weight, not getting enough physical activity, eating a diet high in salt, drinking more alcohol than recommended and smoking.
In some people, high blood pressure has a more specific underlying cause, such as kidney disease, narrowing of the arteries that supply the kidneys, hormonal conditions, certain medicines or drugs, sleep apnoea or complications of pregnancy. This is known as secondary hypertension, because another condition is driving the high blood pressure, and treating that condition can bring it back down.
Can you lower your blood pressure?
Often, yes. The same lifestyle factors that push blood pressure up are also the levers for bringing it down, and changing them can help prevent hypertension as well as manage it once you have it. The 2025 US guideline strongly recommends lifestyle changes for all adults, whatever their blood pressure.
Stay physically active
Regular physical activity helps lower blood pressure and improves your overall heart health. You don’t need to start with an intense program; walking, cycling and swimming all count. If you have an existing health condition or have not exercised for a while, check with your doctor about what level of activity suits you.
Watch your weight
Carrying extra weight increases the risk of high blood pressure. If you are overweight, losing some of it can improve your blood pressure along with other aspects of your cardiovascular health.
Cut back on salt
A diet high in sodium contributes to high blood pressure, and most of the salt in the Australian diet comes from processed and packaged foods such as bread, sauces and ready meals rather than the salt shaker. Checking food labels and choosing less processed foods makes a real difference.
Keep alcohol within the guidelines
The NHMRC alcohol guidelines recommend that healthy adults drink no more than 10 standard drinks a week and no more than 4 on any one day, and note that the less you drink, the lower your risk.
Don’t smoke
Smoking damages blood vessels and increases cardiovascular risk. If you smoke, quitting brings substantial health benefits at any age.
Get enough sleep
Poor sleep and conditions such as sleep apnoea are linked with high blood pressure. If you snore heavily, stop breathing during sleep or feel unusually tired during the day, it is worth raising with your doctor.
Manage stress
Stress raises blood pressure in the moment, and ongoing stress makes healthy habits harder to keep up. Finding ways to manage it, alongside sleeping well and staying active, is a useful part of looking after your heart.
Lifestyle changes are not always enough on their own. Some people also need medication to control their blood pressure, and the right treatment depends on their individual circumstances and overall risk, which is a conversation to have with a GP.
How to check your blood pressure at home
If your doctor has asked you to monitor your blood pressure at home, technique matters. Healthdirect recommends sitting quietly for five minutes first, with your feet flat on the floor, legs uncrossed and your back and arm supported. Avoid caffeine and smoking for 30 minutes beforehand, empty your bladder, and take two readings a minute apart. Use an automatic upper-arm monitor with a cuff that fits properly; wrist and finger monitors are not recommended, and the Menzies Institute keeps a list of validated devices.
Try to take your readings under similar conditions each time, ideally at around the same time each morning and evening. That makes it much easier for you and your doctor to see whether your blood pressure is genuinely changing, rather than just reacting to what you were doing beforehand. And don’t rely on a smartwatch as a substitute: the 2025 US guideline specifically warns against relying on cuffless devices until their accuracy improves.
The short version
Blood pressure is the force of blood pushing against your artery walls, recorded as two numbers: systolic pressure when your heart contracts, and diastolic pressure when it relaxes. In Australia, 140/90 mmHg or higher is considered high, while the US draws the line at 130/80, and your doctor will look at repeated readings and your overall health rather than a single number. Many people find their readings are higher at the doctor’s thanks to white coat hypertension, which is why home monitoring is so useful.
High blood pressure is common, affecting around 2 in 5 Australian adults, and it usually has no symptoms, so regular checks are the only way to know. The good news is that staying active, keeping to a healthy weight, cutting back on salt, limiting alcohol and not smoking all help. If you are concerned about your blood pressure, or you keep getting high readings at home or at the doctor’s, speak with your GP.
This article is for general information only and is not a substitute for medical advice. If you are concerned about your blood pressure or your health, please speak with a qualified health professional.
Sources
- Healthdirect: High blood pressure (hypertension)
- Healthdirect: What is a healthy blood pressure?
- Healthdirect: Blood pressure monitoring at home
- Australian Institute of Health and Welfare: How common is hypertension?
- Heart Foundation: Hypertension clinical information and guidelines
- Heart Foundation: Blood pressure and your heart
- NHMRC: Australian guidelines to reduce health risks from drinking alcohol
- American Heart Association: Top things to know, 2025 high blood pressure guideline
- Cureus: White coat hypertension in primary care, a narrative review (2025)
- European Society of Cardiology: White-coat hypertension, not so innocent
- Menzies Institute for Medical Research: Validated blood pressure devices (PDF)