Most of the time, you can’t feel high blood pressure. It rarely causes noticeable symptoms until it’s severe enough to damage organs, which is why it’s often called “the silent killer.” The only reliable way to know if your blood pressure is high is to measure it. An estimated 13% of U.S. adults have undiagnosed hypertension, meaning their blood pressure is elevated and they don’t know it.
What the Numbers Mean
Blood pressure is recorded as two numbers. The top number (systolic) measures the pressure when your heart beats. The bottom number (diastolic) measures the pressure between beats. Both matter, and if they fall into different categories, the higher category applies.
- Normal: below 120/80
- Elevated: 120 to 129 systolic, with 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 isn’t hypertension yet, but it’s a warning sign. Without changes, it tends to climb into Stage 1 territory over time.
Why You Probably Won’t Feel It
High blood pressure in the Stage 1 or Stage 2 range typically causes no symptoms at all. You won’t feel dizzy, flushed, or “off.” That’s what makes it dangerous. It can quietly damage your arteries, heart, kidneys, and brain over years without giving you any signal that something is wrong.
The symptoms people sometimes associate with high blood pressure, like headaches or nosebleeds, don’t reliably show up until blood pressure reaches extremely high levels. When blood pressure spikes to crisis levels (usually well above 180/120), you may experience chest pain, severe shortness of breath, headache, vision changes, or neurological symptoms like confusion or difficulty speaking. In one study of hypertensive emergencies, chest pain was present in 93% of cases and shortness of breath in 71%. These situations require immediate emergency care.
How to Check Your Blood Pressure
You can get a reading at a pharmacy kiosk, a doctor’s office, or with a home monitor. Home monitors with an upper-arm cuff are widely available and generally accurate when used correctly. The CDC recommends this routine:
- Sit quietly for at least 5 minutes with your back supported before measuring.
- Rest your arm on a table at chest height with the cuff against bare skin.
- Keep both feet flat on the floor, legs uncrossed.
- Don’t talk during the reading.
- Avoid food, drinks, and caffeine for 30 minutes beforehand, and empty your bladder first.
- Take at least two readings one to two minutes apart, and average them.
Try to measure at the same time each day, since blood pressure naturally fluctuates throughout the day. Morning and evening readings give the most useful picture.
Cuff Size Matters More Than You Think
Using the wrong cuff size can throw off your reading significantly. In a randomized trial of 195 adults, people who needed a large cuff but used a regular one got readings that were nearly 5 points too high on the systolic number. For those who needed an extra-large cuff, a regular cuff inflated the reading by almost 20 points, enough to make a normal blood pressure look like Stage 2 hypertension. If the cuff is too large for your arm, it can read about 4 points too low. Most home monitors come with a standard cuff, so check the arm circumference range printed on it and size up or down if needed.
One High Reading Isn’t a Diagnosis
A single elevated reading doesn’t mean you have hypertension. Stress, caffeine, a full bladder, or even rushing to your appointment can temporarily push your numbers up. Clinical guidelines require elevated readings on at least two separate occasions before diagnosing hypertension. Some guidelines recommend tracking over three to five visits, and in the UK, doctors typically confirm a diagnosis with a 24-hour ambulatory monitor that takes readings automatically throughout your day, averaging at least 14 measurements during waking hours.
If ambulatory monitoring isn’t an option, home monitoring over seven days (measuring morning and evening, then discarding the first day’s readings and averaging the rest) is considered a solid alternative. This approach catches patterns that a single office visit can miss.
Your Office Reading Might Not Tell the Whole Story
Some people consistently read high at the doctor’s office but have normal blood pressure the rest of the time. This is called white coat hypertension, and it accounts for 25% to 30% of people seen at hypertension clinics. It’s diagnosed when office readings are above 140/90 on at least three visits, but out-of-office averages stay below 135/85.
The opposite pattern is more concerning. Masked hypertension means your blood pressure looks normal in the office but runs high the rest of the time. This affects an estimated 15% to 30% of people and carries real cardiovascular risk because it often goes undetected. Home monitoring or a 24-hour ambulatory device is the only way to catch it.
How Often to Get Checked
The U.S. Preventive Services Task Force recommends annual screening if you’re 40 or older, or if you have risk factors like being overweight, having readings in the high-normal range, or being Black (a population with higher rates of hypertension). If you’re 18 to 39 with no risk factors and your last reading was normal, screening every three to five years is generally sufficient.
If you already own a home monitor, there’s no downside to checking more frequently. Keeping a log of your readings gives your doctor far more useful information than a single number taken in the office. Write down the date, time, and both numbers, or use a monitor that stores them automatically.