What the two numbers mean
In a reading like 120/80, the top number (systolic) is the pressure in your arteries when your heart beats. The bottom number (diastolic) is the pressure between beats, while your heart refills. Both are measured in millimeters of mercury (mmHg).
Why both numbers matter
Doctors used to focus mostly on the bottom number. A large study of about 1.3 million adults (Kaiser Permanente, published in the New England Journal of Medicine in 2019) found that a high top number and a high bottom number each predicted heart attack and stroke on their own — the top number had the bigger effect.
Why the top number gets more attention after 50
The top number tends to rise with age as large arteries stiffen. The American Heart Association says more attention is usually given to the top number as a risk factor for people over 50. A high top number with a normal bottom number (for example 160/78) is called isolated systolic hypertension.
Either number can make a reading high
| Category | Top number | Bottom number |
|---|---|---|
| Normal | Under 120 | and under 80 |
| Elevated | 120–129 | and under 80 |
| Stage 1 | 130–139 | or 80–89 |
| Stage 2 | 140 or higher | or 90 or higher |
| Hypertensive crisis | Higher than 180 | and/or higher than 120 |
Contact your doctor in the crisis range. With symptoms like chest pain, shortness of breath, weakness or trouble speaking, call 911.
In the table, "or" means either number counts — 119/98 is stage 2 because of the bottom number.
What to do
Take readings the right way (see How to get an accurate blood pressure reading), look at your average over days rather than one number, and share your readings with your doctor if either number is often high.
How FourNumbers helps
FourNumbers shows where each reading sits using both numbers, compares it with your 2-week average, and keeps a log you can share with your doctor.
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Sources
- Flint AC et al. Effect of Systolic and Diastolic Blood Pressure on Cardiovascular Outcomes. N Engl J Med 2019
- American Heart Association: Understanding Blood Pressure Readings
- US Preventive Services Task Force: Abdominal Aortic Aneurysm Screening (2019)
Related guides
- How do I get an accurate blood pressure reading with my cuff?
- Should I measure blood pressure in the morning or evening?
- How do I keep a blood pressure log for my doctor?
Last checked: October 2026.