How to measure your blood pressure at home and get accurate readings

Home blood pressure readings are often more useful to a doctor than the one taken in the clinic, but only if they are taken properly. Small things — a cuff that is too small, talking, a full bladder — can add 10 mmHg or more. This guide covers the routine, and the blood pressure log keeps the results tidy.

Why home readings matter

Many people's blood pressure is higher in a clinic than at home, an effect called white-coat hypertension; others have the reverse, masked hypertension, where clinic readings look fine and home readings are high. Readings taken at home over several days average out these effects and day-to-day variation, which is why guidelines such as NICE in the UK use home or ambulatory readings to confirm a diagnosis. Home monitoring also shows whether treatment or lifestyle changes are working.

Choosing a monitor

Use an automatic upper-arm monitor that has been clinically validated; independent lists of validated devices are published in many countries, for example by the British and Irish Hypertension Society and, in the US, the Validate BP list. Wrist and finger monitors are more sensitive to arm position and are generally less accurate. The cuff size matters as much as the monitor: a cuff that is too small reads high and one that is too large reads low. Measure around the middle of your upper arm and choose the cuff whose stated range includes it; many monitors come with a medium cuff and offer large ones separately.

The routine for an accurate reading

• Avoid caffeine, smoking and exercise for 30 minutes beforehand, and empty your bladder.
• Sit in a chair with your back supported and feet flat on the floor, legs uncrossed.
• Rest your arm on a table so the cuff is at the level of your heart, on bare skin rather than over a sleeve.
• Sit quietly for five minutes before measuring, and don't talk or look at your phone during the reading.
• Take two readings about a minute apart and record both.
• Use the same arm each time; if a doctor has found a difference between arms, use the higher one.

Unusual readings are common the first few times; that is one reason the first day of a series is often discarded.

How many readings to take

For a check before an appointment, a common schedule (used by NICE) is two readings a minute apart, twice a day, morning and evening, for at least four days and ideally seven. Discard the first day and average the rest. Morning readings are best taken before medication and breakfast, and evening ones before dinner; if you take tablets at set times, the medication schedule maker helps fit readings around them. For ongoing monitoring once you know your numbers, a week of readings every month or so is usually enough unless your doctor asks for more. Measuring many times a day tends to cause worry rather than insight.

Recording and sharing

Write down the date, time, both numbers, pulse and anything unusual, such as feeling stressed or having just had coffee. The blood pressure log does this, shows each reading's category, averages the last 7 and 30 days and morning against evening, and prints a report or exports a CSV for your appointment; it saves everything only in your browser. Bring the average rather than your single best or worst reading, and remember that home thresholds are slightly lower than clinic ones: NICE uses a home average of 135/85. What is a normal blood pressure? How to read the numbers explains the categories, and the blood pressure checker explains a single reading.