The protocol guidelines ask for is two readings at each sitting, one to two minutes apart, twice a day — morning and evening — for seven consecutive days, with the first day thrown away under NICE guidance and everything else averaged. That is roughly 24 readings feeding one number. The reason for so many is that a single measurement carries too much noise to act on, and the average is what clinicians actually compare against the home threshold of 135/85 mmHg used by NICE and the ESC.
How many readings should I take at each sitting?
Two, taken one to two minutes apart, after sitting quietly for five minutes. The first reading in a sitting is very often the highest, because the act of settling down and starting the machine raises the pressure slightly; the second is usually closer to the truth. Some clinicians ask for a third if the first two disagree substantially, and if yours does, they will tell you the gap they care about.
How many days in a row do I need?
Seven consecutive days is the standard request; when seven is not practical, the 2024 ESC guidelines accept at least three days and NICE at least four. Consecutive matters more than people expect: a week of measurements captures the ordinary rhythm of your life, whereas readings scattered across a month tend to cluster around the days you felt like measuring, which is not a random sample of your blood pressure.
Why is the first day thrown away?
Because first-day readings are reliably higher than the rest. The novelty of the device, the uncertainty about whether you are doing it right, and the attention you are paying all lift the number. Discarding day one is not tidying the data to look better; it is a standing instruction in NICE guideline NG136 precisely because that day is known to be unrepresentative, although the 2024 ESC guidelines average all readings, day one included.
Do I average everything together, or morning and evening separately?
Both are useful and they answer different questions. The overall average across the week is the number compared against the threshold, while separate morning and evening averages show the shape of your day, which matters if a treatment is timed. Keep the raw readings either way, because an average without the readings behind it cannot be re-checked by the person reading it.
What if I miss a day or a session?
Note the gap and carry on rather than starting over. A missed evening is not a ruined week, and honest gaps are far more useful to a clinician than a log quietly back-filled from memory. What does spoil a week is changing something mid-way without recording it: a different arm, a different cuff, or readings that move from before to after your medication.
Is it worth measuring more often than this?
Usually not, and often it is counterproductive. Measuring many times a day tends to produce anxiety rather than information, because you start reacting to normal variation, and normal variation is large: a 10 to 15 point swing between two readings minutes apart is ordinary. Guidelines set a protocol precisely so the answer comes from a defined week rather than from constant sampling. The arithmetic is where most people abandon the exercise, so a printable log with a column for the average, or the Monitor2Log diary, which reads your monitor from a photo and averages the rows for you, both remove that step.
Sources
- European Society of Cardiology, 2024 guidelines for elevated blood pressure and hypertension, home BP monitoring protocol.
- American Heart Association, home blood pressure monitoring instructions.
- NICE NG136, hypertension in adults: diagnosis and management.
- STRIDE BP, validated home monitors and measurement guidance.
General information only, not medical advice. Your clinician sets the schedule that fits your treatment, and it may differ from the general protocol.