Your blood pressure reading is two numbers that tell you how hard blood is pushing against your artery walls. The top number (systolic) measures that pressure when your heart beats, and the bottom number (diastolic) measures it when your heart rests between beats. A normal reading is below 120/80 mm Hg. Once either number climbs above that threshold, your risk for heart disease and stroke starts rising.
What the Two Numbers Tell You
The top number, systolic pressure, captures the peak force inside your arteries at the moment your heart contracts and pushes blood out. It tends to be the number that rises most noticeably with age, because arteries stiffen over time and absorb less of each heartbeat’s impact.
The bottom number, diastolic pressure, reflects the baseline pressure in your arteries while your heart is relaxing and refilling with blood. A healthy diastolic reading means your arteries aren’t under excessive strain even during the “quiet” phase between beats. Both numbers matter: if either one is elevated, your reading falls into a higher category.
Blood Pressure Categories
The 2025 guidelines from the American Heart Association and American College of Cardiology define four categories:
- Normal: below 120 systolic and below 80 diastolic
- Elevated: 120 to 129 systolic with diastolic still below 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
If your systolic and diastolic fall into two different categories, the higher category is the one that applies. So a reading of 135/75 counts as stage 1 hypertension because of the systolic number, even though the diastolic looks fine.
Why High Blood Pressure Is Harmful
Elevated pressure forces your heart to work harder with every beat, and it gradually damages the walls of your blood vessels. Over years, that damage makes arteries stiffer and narrower, which raises pressure even further in a self-reinforcing cycle.
Even stage 1 hypertension, which many people dismiss as “borderline,” carries real consequences. A large prospective study found that people with stage 1 hypertension had a 36% higher lifetime risk of a type of stroke caused by blocked blood flow to the brain, and a 27% higher lifetime risk of heart attack, compared to people with normal pressure. The population-level impact is significant too: stage 1 hypertension alone accounts for roughly 8% to 23% of all strokes and heart attacks, depending on the specific type of event. These aren’t distant risks reserved for people with severely elevated readings. They begin accumulating at numbers many people wouldn’t consider alarming.
What Affects Your Reading
Blood pressure isn’t a fixed number. It fluctuates throughout the day based on what you’re doing, how you’re feeling, and even what time it is. Physical activity temporarily raises systolic pressure because your heart pumps harder and faster. Mental stress does the same thing through the sympathetic nervous system, your body’s fight-or-flight wiring. These short-term spikes are normal and not harmful on their own.
What can be misleading is getting a reading during one of those spikes and assuming it represents your typical pressure. “White coat hypertension,” where your numbers jump simply because you’re in a medical setting, is common enough that a single office reading isn’t considered reliable on its own. Your body also has a natural daily rhythm: blood pressure typically dips during sleep and rises in the morning. A reading taken right after waking may look different from one taken at noon.
How to Get an Accurate Reading at Home
Home monitoring gives you a much clearer picture than occasional office visits. The technique matters more than most people realize, though, because small errors can shift your reading by 10 points or more. The CDC recommends the following steps:
- Avoid food, drinks, and caffeine for 30 minutes before measuring.
- Empty your bladder before sitting down. A full bladder can raise systolic pressure noticeably.
- Sit with your back supported for at least 5 minutes before taking a reading. Don’t perch on the edge of a chair or exam table.
- Keep both feet flat on the floor with legs uncrossed. Crossing your legs can add several points to your reading.
- Rest your arm on a table at chest height with the cuff against bare skin, not over a sleeve.
- Stay quiet while the cuff is inflating and reading. Talking during a measurement raises the numbers.
Take at least two readings, spaced one to two minutes apart, and use the average. If the first reading seems unusually high, don’t panic. Sit quietly and try again. The pattern across multiple days is far more meaningful than any single measurement.
Do Targets Change With Age?
Current AHA/ACC guidelines apply the same target of below 130/80 to adults of all ages, from 30-year-olds to people in their 80s. In practice, hitting that target gets harder as you get older. Arteries lose elasticity over the decades, which tends to push systolic pressure up while diastolic pressure stays the same or even drops. This pattern, called isolated systolic hypertension, is extremely common in older adults.
For some older people, especially those with stiff arteries and other health conditions, getting below 130 systolic may not be realistic or may cause side effects like dizziness from pressure dropping too low when standing. The guideline is a goal, not an absolute cutoff, and the conversation with a clinician becomes more nuanced with age. What doesn’t change is the basic principle: lower pressure within a safe range means less cumulative damage to your heart, brain, and kidneys.
How Salt Raises Blood Pressure
Your kidneys are the main regulators of blood pressure over the long term. They control how much sodium stays in your body, and sodium pulls water with it. When you eat more salt than your kidneys can efficiently clear, the extra sodium holds onto fluid in your bloodstream, increasing total blood volume. More fluid in the same network of blood vessels means higher pressure against the walls.
This process is managed at the cellular level by a pump on kidney cells that moves sodium and potassium in opposite directions. That pump determines how much sodium gets reabsorbed back into your blood versus how much gets flushed out in urine. In some people, this system is more sensitive to salt intake than in others, which is why two people can eat the same diet and end up with different blood pressure readings. Potassium-rich foods (bananas, potatoes, leafy greens) support the other side of this pump, helping your kidneys excrete more sodium.