A blood pressure reading is two numbers, such as 128/82. For most adults, a clinic reading below 120/80 is considered normal, and readings that stay at 140/90 or higher on different days count as high blood pressure (hypertension) under World Health Organization (WHO) criteria. Home readings run lower, so the NHS treats 135/85 or higher at home as high. The American guideline draws its line lower still, at 130/80.

One reading on its own is not a diagnosis. This guide explains the numbers, why guidelines disagree, how to measure at home, and what to do at different readings.

What the two numbers mean

Blood pressure is measured in millimeters of mercury (mmHg). The NHS explains the two numbers like this:

Systolic (the first or top number) is the highest pressure, when your heart pushes blood around your body.
Diastolic (the second or bottom number) is the lowest pressure, when your heart relaxes between beats.

Blood Pressure UK points out that only one of the numbers needs to be higher than it should be for blood pressure to count as high. A high top number with a normal bottom number is called isolated systolic hypertension.

Blood pressure chart: how the main guidelines define high blood pressure

Guidelines agree on the basics but draw their lines in different places. All figures below are for adults, in mmHg.

WHO

The WHO fact sheet (September 2025) diagnoses hypertension when readings on two different days are 140 or higher systolic and/or 90 or higher diastolic on both days. Very high blood pressure is usually 180/120 or higher.

The WHO 2021 guideline on medicines for hypertension recommends treatment, once the diagnosis is confirmed, at 140/90 or higher for adults in general. It also recommends treatment at a systolic of 130 to 139 for people with existing heart or blood vessel disease, and suggests it for people with high cardiovascular risk, diabetes or chronic kidney disease.

NICE (UK), guideline NG136

NICE sets separate thresholds for clinic readings and for home or 24-hour (ambulatory) readings. NICE guideline NG136 (first published 2019, last updated February 2026) sets these thresholds:

Stage 1: clinic 140/90 or higher, and home or ambulatory average 135/85 or higher
Stage 2: clinic 160/100 or higher, and home or ambulatory average 150/95 or higher
Stage 3: clinic 180/120 or higher (home readings are not needed to confirm this)

NICE recommends basing the diagnosis on readings taken outside the clinic. A cuff worn for 24 hours (ambulatory monitoring) is the gold standard, and home monitoring is the alternative.

American Heart Association and American College of Cardiology (2025)

The 2025 AHA/ACC guideline, published in August 2025, replaced the 2017 version and uses these categories:

Normal: systolic below 120 and diastolic below 80
Elevated: systolic 120 to 129 and diastolic below 80
Stage 1 hypertension: systolic 130 to 139 or diastolic 80 to 89
Stage 2 hypertension: systolic 140 or higher or diastolic 90 or higher

The AHA patient chart adds severe hypertension (above 180 and/or above 120) without symptoms, and hypertensive emergency at the same level with symptoms.

South Africa

The Southern African Hypertension Society's practice guideline (2014) defines hypertension as a persistent office reading of 140/90 or higher, and grades it:

Grade 1: 140 to 159 systolic, or 90 to 99 diastolic
Grade 2: 160 to 179 systolic, or 100 to 109 diastolic
Grade 3: 180 or higher systolic, or 110 or higher diastolic

It uses 135/85 as the threshold for home readings.

Why the guidelines differ

The disagreement is about where to draw the line, not about whether higher pressure is harmful. The American guideline acts earlier, from 130/80. For lower-risk adults with stage 1 readings (130 to 139 / 80 to 89), it recommends 3 to 6 months of lifestyle change first, with medicine if the average stays at 130/80 or higher. For stage 2 readings (140/90 or higher), the AHA advises starting medicine alongside lifestyle changes. WHO, NICE and South Africa keep 140/90 as the line for most adults. Follow the guideline your clinic uses, and watch the trend.

Is 140/90 high?

Yes, if it keeps coming back. Under WHO, NICE and South African criteria, a clinic reading of 140/90 on more than one occasion is at the threshold for hypertension. Under the American categories it is stage 2. At home, it is above the 135/85 line used by the NHS and NICE. A single 140/90 is a reason to measure again properly, not to panic.

How many people have high blood pressure?

The WHO fact sheet gives these figures for 2024:

About 1.4 billion adults aged 30 to 79 had hypertension, about 33% of that age group, and about two thirds of them live in low- and middle-income countries.
About 44% did not know they had it.
About 44% were diagnosed and treated, and only about 23% had it under control.

Most people with hypertension have no symptoms. Left uncontrolled, WHO says, it can damage the heart, kidneys and the arteries to the brain, causing strokes.

Why one reading is not a diagnosis

Blood pressure changes from minute to minute. Stress, temperature, a recent meal, a full bladder, caffeine, smoking, exercise and talking during the test can all affect a reading. That is why WHO asks for readings on two different days, and why NICE confirms a diagnosis with readings outside the clinic.

White-coat effect. The stress of being measured in a clinic can raise your blood pressure temporarily. The US Centers for Disease Control and Prevention (CDC) says as many as 1 in 3 people with a high reading at the doctor's office may have normal readings outside it.
Masked hypertension. This is the opposite: normal clinic readings but high readings elsewhere. The South African guideline says to suspect it when clinic readings are normal but there are signs of damage to organs such as the heart or kidneys.

How to measure your blood pressure at home

Use a clinically validated upper-arm monitor. The AHA says wrist and finger monitors give less reliable readings, and the 2025 guideline advises against relying on cuffless devices such as smartwatches for now. These steps come from AHA, NHS, CDC, NICE and Blood Pressure UK guidance:

Prepare. No smoking, caffeine or exercise in the 30 minutes before. Empty your bladder.
Rest. Sit quietly for at least five minutes.
Sit properly. Sit in a chair with your back supported, feet flat on the floor and legs uncrossed.
Position your arm. Rest it on a table with bare skin under the cuff. The middle of the cuff should sit on your upper arm at heart level.
Check the cuff size. Measure around your upper arm, halfway between shoulder and elbow, and use the matching cuff. The wrong size gives a wrong reading.
Stay quiet. Do not talk while the monitor works.
Take two readings, one minute apart.
Write them down. Record the date, time and both numbers, and bring the log, and ideally your monitor, to appointments.
Be consistent. Measure at the same times each day, usually morning and evening.

Which arm? NICE recommends checking both arms when high blood pressure is first diagnosed, and the South African guideline says to use the arm with the higher reading. Ask your clinic which arm to use at home.

Worked example (illustrative)

NICE's home plan is at least two readings, one minute apart, twice a day for 4 to 7 days. You ignore the first day and average the rest.

Say you measure for 7 days and discard day 1. That leaves 24 readings. If the systolic readings add up to 3,312, the average is 3,312 ÷ 24 = 138. If the diastolic readings add up to 2,088, the average is 87. An average of 138/87 is above the 135/85 home threshold, so share the log with your clinician. These numbers are made up to show the method.

What to do at different readings

If your clinician has given you a personal target, follow it.

Below 120/80: normal. Keep up healthy habits.
120 to 139 systolic or 80 to 89 diastolic: above ideal. Blood Pressure UK calls this "high-normal" and suggests lifestyle changes. Recheck regularly.
140/90 or higher in clinic, or 135/85 or higher on home averages: book a review with a doctor, nurse or pharmacist, and bring your readings.
Around 160/100 or higher on repeated readings: NICE stage 2 and South African grade 2. Arrange an assessment without delay.
180/120 or higher, no symptoms: the AHA advises waiting one minute and measuring again. If it is still that high, contact your healthcare professional promptly.
180/120 or higher with symptoms: treat this as an emergency.

Low blood pressure, briefly

The NHS defines low blood pressure as a reading below 90/60. Blood Pressure UK says low blood pressure that is not causing problems probably won't need any treatment. It matters when it causes symptoms such as dizziness, blurred vision, weakness, confusion or fainting.

Dizziness on standing is called postural hypotension, and Blood Pressure UK links it with ageing and with blood pressure medicines. Get up slowly, and see a doctor if dizziness or fainting keeps happening. Some medicines can also cause low blood pressure, the NHS notes.

Lifestyle steps that help

None of these replaces medicine you have been prescribed.

Cut salt. WHO recommends adults have less than 2,000 mg of sodium a day, equal to less than 5 g of salt, just under a teaspoon. The global average in 2021 was about 11 g of salt a day. WHO suggests flavoring food with herbs and spices instead, and to cut down on processed foods, stock cubes and salt added during cooking and at the table, which are major sources of salt.
Salt substitutes, with care. WHO suggests potassium-containing lower-sodium salt substitutes for people who use table salt, but its 2025 guideline excludes pregnant women, children, and adults with kidney problems or other conditions that affect how the body clears potassium. Check with your pharmacist before switching.
Move more. WHO recommends at least 150 minutes a week of moderate activity, such as brisk walking, or 75 minutes of vigorous activity, plus muscle strengthening on two or more days.
Limit alcohol. The WHO fact sheet suggests no more than one drink a day for women and two for men. The 2025 American guideline strongly recommends reducing or stopping alcohol.
Eat well. More vegetables and fruit, fewer saturated and trans fats. The American guideline strongly recommends a heart-healthy eating pattern such as DASH. If you also have diabetes, our type 2 diabetes food list may help.
Keep to a healthy weight, and do not smoke. WHO lists both among the changeable risk factors.

Medicines, in general terms

The WHO 2021 guideline recommends any of three first-line groups:

thiazide or thiazide-like diuretics ("water tablets")
ACE inhibitors or angiotensin receptor blockers (ARBs)
long-acting dihydropyridine calcium channel blockers, such as amlodipine

WHO suggests that starting with a combination, preferably in a single pill, can help people stay on treatment, with monthly follow-up until blood pressure is controlled and then every 3 to 6 months. Targets vary: WHO aims for below 140/90 for most people, NICE for below 140/90 in clinic (135/85 at home) for people under 80, and the American guideline for below 130/80 for all adults, with some exceptions.

Swollen ankles are a common side effect of amlodipine, and our article on amlodipine side effects and swollen ankles explains what helps. Your prescriber will choose the medicine and set the dose. Do not stop or change it on your own, even when your readings look good.

Painkillers can raise blood pressure. The US prescribing information for ibuprofen warns that NSAIDs (anti-inflammatory painkillers) can cause new high blood pressure or worsen existing high blood pressure, and that blood pressure should be watched closely when starting them. Read can I take ibuprofen with blood pressure medicine? and ask your pharmacist before buying a painkiller.

Other conditions. WHO lists diabetes and kidney disease among the risk factors for hypertension, and suggests a lower systolic target, below 130, for people at high risk. If you have diabetes, our guide to high fasting blood sugar in the morning may help with the sugar side. If you have erection problems, our article on erectile dysfunction and heart health explains why they are worth raising with your doctor.

Questions to ask your doctor or pharmacist

Is my blood pressure high, or do I need home or 24-hour readings to confirm it?
What is my target, and which guideline does this clinic follow?
Is my monitor validated, and is the cuff the right size for my arm?
What reading should make me call you, and what means emergency care?

Frequently asked questions

What is a normal blood pressure?

Under the American categories, a clinic reading below 120/80 is normal. Blood Pressure UK describes 90/60 to 120/80 as the ideal range. Below 90/60 is low, which is usually only a problem if it causes symptoms.

Is 135/85 high at home?

Under NHS and NICE guidance, an average home reading of 135/85 or higher counts as high. Home thresholds are lower because readings at home tend to be lower.

Does high blood pressure cause headaches?

Usually not. WHO and the NHS say most people with high blood pressure have no symptoms. Severe headache can come with very high blood pressure, usually 180/120 or higher, and then needs urgent care.

Can one high reading mean I have hypertension?

Not on its own. WHO uses readings on two different days. But a very high reading with symptoms needs emergency care.

Can I stop my blood pressure tablets once my readings are normal?

Not on your own. Normal readings on treatment usually mean the medicine is working. Talk to your prescriber first.

This article is general information and does not replace advice from your own doctor or pharmacist.

Sources

World Health Organization. Hypertension fact sheet (25 September 2025)
World Health Organization. Guideline for the pharmacological treatment of hypertension in adults (2021), executive summary
World Health Organization. Sodium reduction fact sheet (11 May 2026)
World Health Organization. Physical activity: recommendations for adults
Stellenbosch University. Report on the WHO guideline on lower-sodium salt substitutes (2 April 2025)
National Institute for Health and Care Excellence. Hypertension in adults: diagnosis and management (NG136), last updated February 2026
Jones NR, McCormack T, Constanti M, McManus RJ. Diagnosis and management of hypertension in adults: NICE guideline update 2019. Br J Gen Pract. 2020;70:90-91.
Jones DW, Ferdinand KC, et al. 2025 AHA/ACC/AANP/AAPA/ABC/ACCP/ACPM/AGS/AMA/ASPC/NMA/PCNA/SGIM guideline for the prevention, detection, evaluation and management of high blood pressure in adults. Hypertension. 2025;82(10):e212-e316.
American Heart Association. Top things to know: 2025 high blood pressure guideline (14 August 2025)
American Heart Association. Understanding blood pressure readings (reviewed 14 August 2025)
American Heart Association. Monitoring your blood pressure at home
Seedat YK, Rayner BL, Veriava Y. South African hypertension practice guideline 2014. Cardiovasc J Afr. 2014;25:288-294.
NHS. High blood pressure (reviewed 19 July 2024)
NHS. Blood pressure test (reviewed 25 November 2025)
NHS. Check your blood pressure reading
NHS. Low blood pressure (reviewed 11 July 2023)
NHS. Amlodipine (reviewed 9 June 2026)
Centers for Disease Control and Prevention. Measuring your blood pressure (updated 13 October 2026)
Blood Pressure UK. What do the numbers mean?; What is low blood pressure?; Monitoring your blood pressure at home
DailyMed. Ibuprofen tablets prescribing information (revised 07/2024)