Blood pressure: the most important number you can measure yourself

If you could know only one number about your cardiovascular health, it should probably be your blood pressure. It is cheap to measure, it changes with what you do, and lowering it prevents heart attacks, strokes and heart failure in proportion to how far it falls. Yet it is also one of the most frequently mismeasured numbers in medicine: a single reading in a busy surgery says surprisingly little. The good news is that the most reliable measurement is the one you can take yourself, at home.

Why this number matters so much

The strongest evidence comes from the Blood Pressure Lowering Treatment Trialists' Collaboration, which pooled individual data from 48 randomised trials and 344,716 participants. Each 5 mmHg reduction in systolic pressure (the upper number) lowered the risk of major cardiovascular events by about 10% — in people with and without previous heart disease or stroke, and even when starting pressures were in the normal or high-normal range. There was no threshold below which the benefit stopped.

In absolute terms, among participants without previous cardiovascular disease, major events fell from 31.9 to 25.9 per 1,000 person-years — roughly six fewer events for every 1,000 people treated for a year. How much any individual gains depends on their baseline risk: the same 10% relative reduction is worth far more to a 70-year-old smoker with diabetes than to a healthy 40-year-old. That is why modern guidelines combine blood pressure with an estimate of overall cardiovascular risk rather than treating the number in isolation.

Office, home or 24-hour: which reading counts?

Blood pressure varies from minute to minute. The 2024 European Society of Cardiology (ESC) guideline therefore recommends confirming the diagnosis with measurements outside the doctor's office — either home monitoring or 24-hour ambulatory monitoring, where a portable device measures every 15–30 minutes by day and every 30–60 minutes at night. Because the reference ranges differ, the thresholds differ too:

• Office: hypertension from 140/90 mmHg
• Home (average): hypertension from 135/85 mmHg
• 24-hour ambulatory average: hypertension from 130/80 mmHg (night-time from 120/70)

Out-of-office measurement exposes two important patterns. In white-coat hypertension, readings are high in the office (≥140/90) but normal at home (<135/85). In masked hypertension, it is the other way round: normal in the office, high in daily life. Masked hypertension is the more treacherous of the two because it goes unnoticed; the ESC notes it is more common in men, smokers, people who drink heavily, and people with diabetes or obesity. Home and ambulatory monitoring disagree in about 15% of people, so when home readings sit close to a decision threshold, a 24-hour recording can settle the question.

How to measure correctly at home

Home readings are only as good as the device and the technique. The essentials, drawn from the ESC guideline and the German Hypertension League (Deutsche Hochdruckliga):

• Device: use a validated, automatic upper-arm device. Wrist devices can be accurate but are easily misused if the wrist is not held at heart level. The Hochdruckliga tests devices and awards a seal of approval (Prüfsiegel); its website lists approved upper-arm and wrist models by year. It advises against cuffless wearables for blood pressure measurement.
• Cuff size: measure your upper-arm circumference and choose a matching cuff. The ESC specifies an inflatable bladder covering 75–100% of the arm's circumference.
• Position: sit quietly for five minutes, arm relaxed and supported with the cuff at heart level, the lower edge about two finger-widths above the elbow crease. Do not talk during the measurement.
• Which arm: measure both arms the first time; afterwards use the arm with the higher readings.
• Protocol: take two readings, one to two minutes apart, every morning and every evening at the same times. Morning readings go before breakfast and before any medication. Do this for at least three and ideally seven days, then average all readings. The Hochdruckliga suggests such a measuring week at diagnosis, after any change in treatment and, once stable, about once a month.
• Check your device: the ESC suggests replacing devices older than about four years if they prove inaccurate. The Hochdruckliga describes a simple check against a manual reading: three paired measurements on the same arm should differ by no more than about 10 mmHg on average.

Categories and targets: Europe vs the US

The 2024 ESC guideline introduced three categories based on office readings: non-elevated (<120/70 mmHg), elevated (120–139 systolic or 70–89 diastolic) and hypertension (≥140/90). People with confirmed hypertension should be treated. For those with elevated blood pressure, the decision depends on overall risk: a 10-year cardiovascular risk of 10% or more (estimated with SCORE2, or SCORE2-OP from age 70), or conditions such as diabetes, chronic kidney disease, established cardiovascular disease or familial hypercholesterolaemia, justify treatment — beginning with three months of lifestyle measures, followed by medication if these are not enough. On treatment, the ESC recommends a systolic target of 120–129 mmHg provided it is well tolerated, with more lenient goals for people aged 85 or older, the frail, or those with symptomatic drops in blood pressure on standing.

The labels differ, but the direction is the same on both sides of the Atlantic: lower is better, risk matters, and the decision should rest on confirmed, out-of-office readings.

What lifestyle changes achieve, in mmHg

Lifestyle effects are real and measurable — and they add up:

• Weight loss: about 1 mmHg lower systolic pressure per kilogram lost (meta-analysis of 25 trials).
• Less salt: cutting about 4.4 g of salt per day lowered systolic pressure by about 4 mmHg overall and about 5 mmHg in people with hypertension.
• Diet pattern: in the DASH trial, a diet rich in vegetables, fruit and low-fat dairy lowered systolic pressure by 5.5 mmHg overall and by 11.4 mmHg in participants with hypertension.
• Exercise: aerobic and resistance training each lowered systolic pressure by about 4–5 mmHg, combined training by about 6 mmHg and isometric training (holding a muscle contraction, such as a handgrip or wall sit) by about 8 mmHg.

Seen against the trial data, a 5 mmHg fall from lifestyle alone corresponds to roughly the same 10% relative risk reduction as a tablet.

For other ways to refine your risk estimate, see our articles on the coronary calcium score and exercise versus medication.

This article is general information and not individual medical advice. Decisions about tests and treatment belong in a conversation with your own physician.