Normal blood pressure is less than 120/80 mmHg. The first number (systolic) measures the pressure in your arteries when your heart beats, and the second number (diastolic) measures the pressure between beats, when your heart is resting. These two numbers together tell you how hard your blood is pushing against your artery walls throughout each cardiac cycle.
What the Numbers Mean
A reading of 115/75, for example, means your arteries experience 115 mmHg of pressure each time your heart contracts and 75 mmHg of pressure while it relaxes. Both numbers matter, but systolic pressure (the top number) gets more attention because it rises steadily with age and is a stronger predictor of heart disease and stroke in adults over 50.
Blood pressure is written as a fraction, but the two numbers aren’t mathematically related. You can have a high systolic reading with a normal diastolic reading, or vice versa. Either number being out of range is enough to classify your blood pressure as elevated or high.
Blood Pressure Categories
- Normal: Less than 120/80 mmHg
- Elevated: Systolic 120 to 129 and diastolic less than 80
- High blood pressure, stage 1: Systolic 130 to 139 or diastolic 80 to 89
- High blood pressure, stage 2: Systolic 140 or higher, or diastolic 90 or higher
- Hypertensive crisis: Higher than 180/120 mmHg
It’s worth noting that the World Health Organization uses a slightly different threshold. Internationally, hypertension is defined as 140/90 mmHg or higher, measured on two separate days. For people with heart disease, diabetes, or chronic kidney disease, the WHO recommends a tighter goal of less than 130/80. The stricter American categories reflect large-scale research showing that cardiovascular risk begins climbing well before 140/90.
Why Lower Targets Matter
A major NIH-funded trial called SPRINT followed over 9,000 adults aged 50 and older who had high blood pressure and at least one additional risk factor for heart disease. Participants who were treated to a systolic target below 120 mmHg, rather than the traditional target of 140, had 25% fewer cardiovascular events like heart attacks, heart failure, and strokes. Their overall risk of death dropped by 27%. The lower-target group also showed about a 20% reduction in mild cognitive impairment.
The tradeoff was a higher rate of side effects. People in the intensive treatment group experienced more episodes of low blood pressure and fainting, along with occasional dips in kidney function, though most of those kidney issues were mild and reversed on their own. There was no increased risk of falls, which had been a major concern for older adults.
These findings are a big reason why guidelines now classify 120 to 129 systolic as “elevated” rather than normal. Your risk of heart disease doesn’t suddenly appear at some magic cutoff. It rises gradually as blood pressure climbs.
When Blood Pressure Is Too Low
Low blood pressure is generally defined as a reading below 90/60 mmHg, but the number alone doesn’t always tell the full story. Some people run naturally low without any symptoms. It only becomes a problem when it causes dizziness, lightheadedness, blurred vision, fatigue, or trouble concentrating.
A sudden drop matters more than a consistently low baseline. A change of just 20 mmHg can be enough to make you feel faint. Extreme drops can lead to shock, which shows up as cold and clammy skin, rapid shallow breathing, confusion, and a weak pulse. That situation requires emergency care.
Getting an Accurate Reading
Your blood pressure can swing by 10 to 20 points depending on how you’re sitting, what you’ve been doing, and even whether you need to use the bathroom. A single reading is a snapshot, not a diagnosis. To get a number that actually reflects your baseline, you need to control for the variables.
Sit in a comfortable chair with your back supported for at least five minutes before taking a reading. Keep both feet flat on the floor, legs uncrossed. Rest the arm with the cuff on a table at chest height. Don’t talk during the measurement. Caffeine, exercise, and a full bladder can all push your numbers up temporarily, so avoid those in the 30 minutes beforehand.
Between 15% and 30% of people who show elevated readings in a medical office actually have normal blood pressure the rest of the time. This phenomenon, called white coat hypertension, happens because the stress of a clinical visit temporarily raises your numbers. It can lead to unnecessary treatment, which is why many providers now recommend confirming high office readings with home monitoring over several days. If your office reading is 140/90 or above but your average home readings are consistently lower, the home numbers are likely more representative.
Blood Pressure in Children
Children have lower blood pressure than adults, and what counts as “normal” depends on age, sex, and height. There’s no single number that applies across childhood the way 120/80 does for adults. Instead, pediatric blood pressure is compared against percentile charts. A typical 10-year-old, for instance, averages around 102/61 mmHg. A reading at or above the 95th percentile for their age and height, roughly 119/80 in that same 10-year-old, is considered high.
These numbers rise naturally as children grow. A blood pressure that’s normal for a 15-year-old would be concerning in a 5-year-old. Pediatricians check blood pressure at annual well visits starting at age 3, and they use age-specific reference tables rather than adult cutoffs.
Blood Pressure in Older Adults
Normal blood pressure is still defined as less than 120/80 for older adults, the same as for younger people. But deciding whether and how aggressively to treat elevated readings gets more nuanced with age. Older adults are more likely to have isolated systolic hypertension, where the top number is high but the bottom number stays normal or even drops. This happens because arteries stiffen over time.
The SPRINT trial specifically included adults over 75 and found that intensive blood pressure lowering benefited them too. But treatment decisions for older adults also factor in other health conditions, fall risk, medication burden, and overall fitness. A blood pressure target that’s ideal for a healthy 68-year-old might not be appropriate for a frail 85-year-old on multiple medications.
What Affects Your Numbers Day to Day
Blood pressure is not a fixed value. It fluctuates throughout the day, typically lowest during sleep and highest in the early morning hours. Stress, physical activity, meals, hydration, temperature, and even the position of your body all influence it. This is normal physiology, not a sign of a problem.
What matters clinically is your average over time. If you’re monitoring at home, take readings at the same time each day, ideally morning and evening, for at least a week. Record all of them rather than cherry-picking the best ones. That pattern of numbers gives you and your provider far more useful information than any single measurement.