Free BP TrackerThe two numbers
Blood pressure is written as two numbers, such as 120/80, and measured in millimetres of mercury (mmHg).
- Systolic (the top number) is “the highest level your blood pressure reaches when your heart pumps blood around the body”.
- Diastolic (the bottom number) is “the lowest level your blood pressure reaches when your heart relaxes between each heartbeat”.
The ranges this app uses
Home readings tend to run lower than readings taken at a GP surgery or pharmacy, so UK guidance uses lower cut-offs for home readings. NICE says home and 24-hour monitor readings run about 5 mmHg lower than clinic readings.
| Range | Home reading | Clinic reading (GP, nurse, pharmacy) |
|---|---|---|
| Low | Below 90/60 (home or clinic) | |
| Healthy | 90/60 up to 120/80 (home or clinic) | |
| Slightly raised | Above 120/80, below 135/85 | Above 120/80, below 140/90 |
| High | 135/85 or higher | 140/90 or higher |
| High (stage 2 range) | 150/95 or higher | 160/100 or higher |
| Very high | 170 top or 100 bottom, or higher | 180 top or 120 bottom, or higher |
Where these numbers come from
- Low: the NHS says low blood pressure is “a reading of less than 90/60mmHg”.
- Healthy: “The normal or ideal adult blood pressure is considered to be between 90/60mmHg and 120/80mmHg.” Readings between 120/80 and 140/90 were described as “high normal”.
- High: the NHS says you’re usually considered to have high blood pressure if your reading is 140/90 or higher when checked by a healthcare professional, or 135/85 or higher when checked at home.
- Stage 2: these are NICE’s stage 2 hypertension levels.
- Very high: for clinic readings, NICE defines severe hypertension as a top number of 180 or more, or a bottom number of 120 or more. NICE doesn’t set a “severe” level for home readings. The NHS’s own “check your blood pressure reading” tool treats a home reading of 170/100 or more as very high, so we use that, more cautious, line.
Either number counts
A reading goes into the highest range that either number reaches. So 128/92 at a clinic counts as high, because the bottom number is 90 or more. NICE’s clinical summary says that if either the systolic or diastolic measurement fits a stage 1 definition, it should be classed as stage 1.
How official sources differ
We’ve chosen the more cautious figure where official sources disagree, and we want to be open about it:
- The NHS reading tool only looks at the top number when deciding if a reading is low or healthy. The NHS low blood pressure page says “less than 90/60”, which we follow.
- Below the “high” level, the NHS tool doesn’t let the bottom number change the range. We count a bottom number above 80 as slightly raised, in line with the 90/60 to 120/80 ideal range.
- The 90/60 to 120/80 “ideal” wording comes from a 2017 Public Health England page on GOV.UK. It no longer appears on the current NHS website pages.
One reading can’t diagnose you
Blood pressure changes through the day. A single high reading doesn’t mean you have high blood pressure. To confirm it, NICE recommends a series of readings, either from a 24-hour monitor or from home readings taken twice a day for at least 4 days, ideally 7. Our 7-day home check follows that method.
NICE stages of high blood pressure
Doctors use these stages, based on an average of readings rather than a single one. ABPM means a 24-hour ambulatory monitor you wear. HBPM means home blood pressure monitoring.
| Stage | Clinic reading | ABPM daytime or HBPM average |
|---|---|---|
| Stage 1 | 140/90 to 159/99 | 135/85 to 149/94 |
| Stage 2 | 160/100 or higher, but less than 180/120 | 150/95 or higher |
| Severe | Top number 180 or more, or bottom number 120 or more | Not defined by NICE |
Hypertension is confirmed when a clinic reading is 140/90 or higher and the ABPM daytime average or HBPM average is 135/85 or higher.
White-coat and masked hypertension
- White-coat effect: a difference of more than 20/10 mmHg between clinic readings and the average home or 24-hour monitor readings at diagnosis. In other words, your blood pressure is higher at the surgery.
- Masked hypertension: clinic readings below 140/90, but higher readings outside the clinic.
Checked against NHS and NICE guidance on . See all official sources.