Checking your blood pressure: why and how?
In short: high blood pressure almost never hurts, yet for years it damages the heart, brain and kidneys. In Belgium, among people aged 40 to 79, more than four in ten have blood pressure that is too high, and almost half of them do not know it. The only way to find out: measure it. The link between high blood pressure and heart attack or stroke is proven, and so is the benefit of lowering it. At home the rule is simple: a validated upper-arm monitor, seated and calm for five minutes, two readings in the morning and two in the evening for a week, then the average. A home average of 135/85 or more warrants an appointment with your doctor. To get equipped, see the section "Choosing a monitor" and the example available from Coolblue.
Updated on 2 November 2026.
It is called the "silent killer". In September 2025 the World Health Organization (WHO) counted 1.4 billion adults with hypertension worldwide, barely one in five of whom has it under control. The 2024 European and 2025 American guidelines point the same way: measure earlier, more often, and preferably at home. Here is why, how to do it without getting it wrong, and how we ended up with a cuff that fits in a drawer.
What is blood pressure?
With each beat, the heart pushes blood into the arteries. Blood pressure is the force this blood exerts on their walls. It is expressed as two numbers:
- systolic, the top number: the pressure when the heart contracts;
- diastolic, the bottom number: the pressure when the heart relaxes between beats.
The unit is the millimetre of mercury (mmHg), a reminder of the first devices in which pressure pushed up a column of mercury. In French-speaking countries doctors often say "13/8", in centimetres: that means 130/80 mmHg. Cardiologists now prefer the full form, which is more precise.
Blood pressure is not a fixed number. It rises when you move, talk, feel cold or are stressed; it falls during sleep. That is why a single reading means almost nothing: what counts is the average of several readings taken under good conditions.
Why measure it?
Because you cannot feel high blood pressure. Headaches, nosebleeds or a red face are poor indicators: most people with hypertension have no symptoms, sometimes for decades.
Meanwhile, excessive pressure wears down the artery walls. It promotes heart attack, stroke, heart failure, kidney disease, atrial fibrillation (a heart rhythm disorder) and cognitive decline.
Two major studies give the order of magnitude:
- Risk starts rising from 115/75. In 2002 a meta-analysis (a study that pools other studies) covering one million adults in 61 studies showed that, between the ages of 40 and 69, each difference of 20 mmHg in systolic (or 10 in diastolic) pressure goes with about twice as many deaths from stroke and from coronary heart disease. There is no threshold below which risk stops falling, at least down to 115/75. Level of evidence: observational, but very large and consistent.
- Lowering blood pressure protects. In 2016 a meta-analysis of 123 controlled trials (more than 600,000 participants) showed that a 10 mmHg drop in systolic pressure cuts major cardiovascular events by about 20%, strokes by 27%, heart failure by 28% and total mortality by 13%. Level of evidence: controlled trials, strong.
And in Belgium? An analysis of Sciensano's health surveys (2018), published in 2024, estimates that 43% of Belgians aged 40 to 79 have high blood pressure. Almost all had had their blood pressure measured in the previous five years, but only 57% of them knew they had hypertension, and fewer than a quarter had it under control. The authors' conclusion: the main obstacle in Belgium is diagnosis. An occasional reading at the doctor's is not enough to make it.
Blood pressure is not the only factor: cholesterol, smoking, diabetes and inactivity add up. Doctors think in terms of overall risk (see our article on fats and cholesterol).
The numbers to know
Thresholds depend on where you measure: blood pressure is usually a little lower at home than at the surgery. Here are those of the European Society of Cardiology (ESC, 2024):
| Category | At the surgery | At home (average) | What it means |
|---|---|---|---|
| Non-elevated | below 120/70 | below 120/70 | Nothing special to do, recheck regularly |
| Elevated | 120-139 / 70-89 | 120-134 / 70-84 | Lifestyle; treatment if cardiovascular risk is high |
| Hypertension | 140/90 or more | 135/85 or more | To be confirmed, then treated with your doctor |
It is enough for one of the two numbers to exceed the threshold. At 142/78 you are in the "hypertension" box.
New in 2024: the "elevated blood pressure" category, between 120/70 and 139/89. It does not mean "ill", but it signals a risk that can already be measured. In treated patients the ESC aims for a systolic pressure between 120 and 129 if treatment is well tolerated, with more lenient targets after 85 or in frail people.
In the United States, the American Heart Association and American College of Cardiology guideline (AHA/ACC, August 2025) keeps lower thresholds (hypertension from 130/80) and a target below 130/80 for most adults. Both texts agree on the essentials: confirm the diagnosis with readings outside the surgery, at home or over 24 hours.
Does this concern me?
| Your situation | What to do? |
|---|---|
| Under 40, non-elevated blood pressure | A reading at least every three years (ESC) |
| 40 or over, or "elevated" blood pressure | A reading at least once a year |
| High reading at the surgery, or high cardiovascular risk (diabetes, smoking, cholesterol, kidney disease, family history) | Confirm with a week of home monitoring or a 24-hour recording |
| Treated hypertension | Regular home monitoring, especially after a change of treatment |
| Pregnancy | Checks as part of antenatal care; report any high reading to your midwife or doctor |
These frequencies are a minimum. Nothing stops you measuring more often, provided you follow the method and do not draw conclusions from a single reading.
Why measure at home?
At the surgery you have climbed the stairs, you talk, you are a little tense. The result is two classic traps:
- The white coat effect: high blood pressure at the doctor's, normal at home. Depending on the study, it affects 15 to 25% of people classed as hypertensive on surgery readings alone. Without home readings, they risk unnecessary treatment.
- Masked hypertension: the opposite. Normal at the surgery, high in everyday life, more common in smokers and in people with a family history. It is linked to more complications than truly normal blood pressure, and it goes unnoticed without home readings.
Home monitoring gives many more numbers, under conditions close to real life. The 2024 European and 2025 American guidelines put it at the heart of diagnosis and follow-up. Ambulatory 24-hour monitoring (a device worn day and night) remains the reference when in doubt, notably for night-time blood pressure.
How to check your blood pressure properly
The method matters as much as the device. Here is the procedure recommended by the medical societies.
Before measuring
- No coffee, tea, tobacco or exercise in the previous 30 minutes.
- Empty bladder.
- In the morning, measure before taking your medicines (without delaying or skipping them) and before breakfast.
Position
- Sitting on a chair, back supported, feet flat on the floor, legs uncrossed.
- Bare arm (no rolled-up sleeve squeezing it), resting on a table, the cuff at heart level.
- The lower edge of the cuff about 2 cm above the crease of the elbow, the tube in line with the arm.
The reading
- Five minutes of rest before the first reading, without phone or screen.
- Do not talk and do not move during the reading.
- Two readings one minute apart, and record both (most devices store them).
- The first time, measure both arms; afterwards, always use the arm that gives the higher value. A large, repeated difference between the two arms should be reported to your doctor.
The one-week protocol, for a diagnosis or after a change of treatment:
| Morning | Evening | |
|---|---|---|
| Day 1 | 2 readings | 2 readings |
| Days 2 to 7 | 2 readings | 2 readings |
| Calculation | Average of all readings, often excluding day 1 |
In France people sometimes speak of the "rule of 3": three readings, morning and evening, three days in a row. Guidelines ask for at least three days, ideally seven. Most clinics discard the first day, which is often higher; this point is debated, but it makes little difference over a full week. Bring the sheet (or the app) to your doctor rather than a single number "just to see".
Outside these monitoring weeks, one series a month or a quarter is often enough for stable blood pressure. Your doctor will tell you which rhythm suits you.
The video below, from the University of Ottawa Heart Institute, shows these steps (in French).
Mistakes that distort the reading
A 2017 systematic review examined 328 studies on sources of error. Of the 29 factors studied, 27 changed the reading significantly, by -24 to +33 mmHg for systolic pressure. The most common:
| Mistake | Effect on the reading |
|---|---|
| Talking during the reading | falsely high systolic, by 4 to 19 mmHg depending on the study |
| Cuff too small for the arm | value too high |
| Cuff too large | value too low |
| Arm hanging by the side, below heart level | value too high |
| Back unsupported, legs crossed | value a few mmHg too high |
| Full bladder, coffee or a cigarette just before | value too high |
| Reading over clothing or a rolled-up sleeve | inaccurate reading |
| Reading right after arriving | value too high |
Cuff size is a frequent trap for people with large arms: measure your arm circumference halfway up and check it falls within the range printed on the cuff (often 22 to 42 cm; larger cuffs exist).
Choosing a monitor
Upper arm rather than wrist. A wrist monitor is more sensitive to position (the wrist must be exactly at heart level) and less reliable. Guidelines recommend an automatic, upper-arm device. A wrist monitor is only worth considering if the arm is too large for the available cuffs.
Validated, not just "CE certified". The CE mark does not guarantee clinical accuracy. Only a small share of the blood pressure monitors sold worldwide, about 6 to 15% according to estimates, has passed validation under a recognised protocol. To check a model, look up its name and model number (HEM-…, BP…) on STRIDE BP (stridebp.org), an independent scientific initiative supported by the European Society of Hypertension, or on the list of the British and Irish Hypertension Society (bihsoc.org).
Useful features:
- memory and automatic averaging (or an app) so you do not have to copy numbers;
- a cuff-placement indicator;
- two user profiles if two people use it;
- atrial fibrillation detection: useful after 65, but it is screening, not diagnosis (an electrocardiogram is still needed).
How much does it cost? A good validated upper-arm monitor costs between 40 and 80 euros. More expensive is not more accurate: you mainly pay for app connectivity or design.
Example: the Omron X3 Comfort AFib (model HEM-7196-FLEO), a one-button upper-arm monitor with a 22-42 cm cuff and atrial fibrillation detection, featured in Coolblue's selection. The seller presents it as validated; check the model number of the device you buy on STRIDE BP.
What about smartwatches? Since September 2025 some watches (including the Apple Watch, cleared in the United States by the FDA) can flag possible hypertension after analysing the pulse for 30 days. They do not measure blood pressure and do not detect every case. The 2025 American guideline advises against cuffless devices (watches, rings) for making a diagnosis or adjusting treatment. An alert of this kind should be followed by a week of home readings with a proper monitor.
Every two or three years, have your device checked by your doctor or pharmacist by comparing its readings with theirs.
A little history
1733: a mare and a glass tube. The English clergyman Stephen Hales published the first measurement of the pressure of the blood. He inserted a brass pipe into the artery of a mare tied on her back and connected it to a nine-foot glass tube: the blood rose more than 2.4 metres. The method was fatal for the animal and unusable in humans.
1828: mercury. The French physician Jean Poiseuille replaced the long tube with a much shorter mercury manometer. Hence our millimetre of mercury. But a cannula still had to be inserted into the artery.
1896: the cuff. The Italian internist Scipione Riva-Rocci presented, in the Gazzetta Medica di Torino, an inflatable cuff that went around the arm, linked to a column of mercury. You inflate until the pulse disappears at the wrist: the pressure read gives the systolic value. The first cuff, 5 cm wide, was too narrow; it was soon widened.
1905: the sounds. The Russian military surgeon Nikolai Korotkoff described, in a few hundred words, the sounds heard through a stethoscope below the cuff as it is deflated. The appearance of the sounds marks the systolic pressure, their disappearance the diastolic. This is the "auscultatory" method doctors used throughout the 20th century.
1945: the president who was not treated. At the time, blood pressure rising with age was thought to be normal, even necessary. Franklin D. Roosevelt had 140/100 in 1932; he died in April 1945 of a cerebral haemorrhage, with blood pressure measured at 300/190. His death helped launch, in 1948, the Framingham study, which follows thousands of residents of a small town in Massachusetts. Its first major results, in the late 1950s, established that hypertension multiplies the risk of heart attack.
From the 1970s to today: blood pressure at home. The first monitors for consumers appeared in Japan in 1973; electronic oscillometric devices (which analyse the vibrations of the artery in the cuff, without a stethoscope) spread in the 1980s. In Europe, mercury sphygmomanometers have been banned from sale to the general public since 2009, and in hospitals and surgeries since 10 April 2014 (REACH regulation). Today the device fits in a drawer and sends its readings to your smartphone.
True or false: common beliefs
"I feel fine, so my blood pressure is normal." False. Hypertension usually has no symptoms. Headaches are not a good signal.
"It's normal for blood pressure to rise with age." It is common, but not without consequences. For a long time it was thought harmless; the Roosevelt case and the Framingham study showed otherwise. Targets are simply more lenient in very old or frail people.
"One high reading at the doctor's means hypertension." Not necessarily. A single reading is not enough: repeated readings are needed, ideally at home.
"A wrist monitor is just as good." Rather false. It is more sensitive to position and less reliable; guidelines prefer the upper arm.
"130/80 is perfect." It depends. 130/80 at the surgery falls into the ESC's "elevated blood pressure" category (120-139 / 70-89). It is not a disease, but a number to keep an eye on, especially if other risk factors are present.
"If my blood pressure is good, I can stop my medicines." False. If it is good, it is often thanks to the treatment. Never stop or change the dose without talking to your doctor.
"Low blood pressure is dangerous." Usually not, in a person without symptoms. Low blood pressure with dizziness on standing, fainting or falls should however be reported, especially under treatment.
When to see a doctor?
- Your home average reaches 135/85 or more: make an appointment with your GP and bring your readings.
- Your readings are regularly around 180/110 or more, without other symptoms: recheck calmly after a few minutes and contact your doctor without delay (the same day if possible).
- Very high blood pressure accompanied by chest pain, breathlessness, a violent and unusual headache, vision or speech problems, or weakness on one side of the body: call 112.
- You are pregnant and your blood pressure is high: report it quickly to your midwife or doctor.
This article gives general guidance; it does not replace the advice of your doctor, who interprets your numbers in the light of your overall risk.
Going further
How does an electronic monitor work? It inflates the cuff until the artery is compressed, then deflates it slowly. A sensor records the small pressure oscillations that the blood transmits to the cuff as it starts flowing again. Their amplitude peaks at mean arterial pressure; an algorithm specific to each manufacturer derives systolic and diastolic values from it. That is why clinical validation of each model is essential: two devices that look identical may use different algorithms.
Do the ESC and AHA disagree? Less than it seems. Europeans keep the 140/90 threshold for hypertension but have created the "elevated" category from 120/70; Americans speak of hypertension from 130/80. In both cases, the decision to treat depends on overall cardiovascular risk, calculated with different tools (SCORE2 in Europe, PREVENT in the United States), and treatment targets are close (systolic below 130).
How good are cuffless readings? Watches, rings and apps estimate blood pressure from the optical pulse or pulse wave velocity. Their accuracy remains insufficient for diagnosis; they often need to be recalibrated against a proper monitor. The alert feature of some watches, cleared in 2025, is a screening tool: it prompts you to measure, it does not replace measuring.
And salt? Cutting down on salt, moving more, limiting alcohol and losing weight if needed all lower blood pressure, sometimes as much as a medicine. Potassium-enriched salt substitutes are now recommended in the United States, except for people with kidney disease or on certain treatments. Magnesium has a modest effect (see our article on magnesium).
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