A “bad” blood pressure reading is anything outside the normal range of less than 120/80 mmHg. That can mean too high (the far more common concern) or too low. A reading of 130/80 or above is considered high blood pressure, while anything below 90/60 is considered low. Both directions carry health risks, though the type and urgency differ significantly.
What the Two Numbers Mean
A blood pressure reading has two numbers. The top number (systolic) measures the force your blood exerts against artery walls when your heart beats. The bottom number (diastolic) measures that force between beats, when your heart is resting. Both numbers matter: if either one crosses into an unhealthy range, the overall reading is considered abnormal. For example, a reading of 135/75 counts as high blood pressure because the top number is elevated, even though the bottom number looks fine.
Blood Pressure Categories
The American Heart Association breaks blood pressure into four categories for adults:
- Normal: Less than 120/80 mmHg
- Elevated: 120 to 129 systolic with a diastolic still under 80
- Stage 1 hypertension: 130 to 139 systolic, or 80 to 89 diastolic
- Stage 2 hypertension: 140 or higher systolic, or 90 or higher diastolic
Elevated blood pressure is a warning zone. It means you’re not yet in hypertension territory, but you’re likely heading there without changes. Stage 1 is where medication may enter the conversation depending on your overall heart disease risk. Stage 2 typically requires both lifestyle changes and medication.
On the low end, a reading below 90/60 mmHg is generally considered hypotension. But low blood pressure is only a problem if it causes symptoms. Some people walk around at 85/55 and feel perfectly fine.
When High Blood Pressure Gets Dangerous
A reading of 180/120 mmHg or higher is a hypertensive crisis. If that number shows up alongside chest pain, shortness of breath, severe headache, blurred vision, or signs of stroke (sudden numbness, trouble speaking, difficulty walking), call 911. This is a medical emergency that can damage organs within minutes.
If you get a reading that high but feel fine, wait five minutes and measure again. A single spike can come from stress, caffeine, or a full bladder. But if it stays at or above 180/120, seek medical attention even without symptoms.
When Low Blood Pressure Is a Problem
Low blood pressure becomes concerning when it causes dizziness, fainting, blurred vision, fatigue, or trouble concentrating. A sudden drop is more dangerous than a consistently low baseline. A fall of just 20 mmHg, say from 110 to 90 systolic, can be enough to make you lightheaded or faint. This commonly happens when standing up quickly, especially in older adults or people who are dehydrated.
Extreme low blood pressure can lead to shock, which has its own distinct warning signs: confusion, cold and clammy skin, rapid shallow breathing, and a weak, fast pulse. Shock is a life-threatening emergency.
What Pushes Blood Pressure Into Unhealthy Ranges
Most high blood pressure develops gradually over years without a single identifiable cause. This is called primary hypertension, and it’s driven by the usual suspects: excess sodium, lack of physical activity, excess weight, chronic stress, smoking, and heavy alcohol use. Family history plays a significant role too.
Sometimes, though, high blood pressure has a specific, treatable cause. This is called secondary hypertension, and your doctor may suspect it if your blood pressure was previously stable but suddenly spikes, you develop high blood pressure before age 30, or your readings stay high despite taking three or more medications. The most common culprits include obstructive sleep apnea, kidney artery narrowing, and hormonal disorders like overproduction of aldosterone.
Several common medications can also raise blood pressure, sometimes significantly. These include decongestants (like those in cold medicines), NSAIDs (common over-the-counter pain relievers), oral contraceptives, corticosteroids like prednisone, and certain antidepressants. Alcohol, nicotine, and some herbal supplements can contribute as well.
Blood Pressure Targets by Age
The 2025 guidelines from the American Heart Association set the treatment goal at less than 130/80 mmHg for all adults, regardless of age. This is a shift from older recommendations that allowed higher targets for elderly patients. For adults 80 and older, treatment is still recommended at 130/80, though doctors weigh the benefits against risks more carefully in people who are frail, institutionalized, or have a limited life expectancy.
How to Get an Accurate Reading
A single reading in a doctor’s office isn’t always reliable. “White coat hypertension,” where anxiety about the visit temporarily raises your numbers, is common. Home monitoring gives a clearer picture over time. But the numbers are only useful if you measure correctly. Small mistakes can swing a reading by 10 to 20 points in either direction.
The CDC recommends this checklist for accurate readings:
- Timing: Don’t eat, drink, or exercise for 30 minutes beforehand. Empty your bladder first.
- Position: Sit in a chair with your back supported for at least five minutes before measuring. Keep both feet flat on the floor, legs uncrossed.
- Arm placement: Rest your arm on a table at chest height. The cuff should be on bare skin, not over clothing.
- During the reading: Don’t talk. Sit still.
Take two readings about a minute apart and average them. If you’re tracking trends at home, measure at the same time each day, ideally morning and evening. Bring your log to medical appointments so your doctor can see the full picture rather than relying on a single in-office number.