A healthy bottom number on a blood pressure reading is below 80 mm Hg. That bottom number, called diastolic pressure, measures the force in your arteries between heartbeats, when your heart is resting and refilling with blood. Once it consistently hits 80 or higher, it falls into the high blood pressure range.
What the Bottom Number Measures
Your blood pressure reading has two numbers. The top number captures pressure while your heart is actively pumping. The bottom number captures pressure during the pause between beats. That resting pressure matters because it reflects how much resistance your arteries are putting up even when the heart isn’t squeezing. A healthy diastolic pressure is critical for your coronary arteries to deliver enough oxygen to the heart muscle itself.
As you age, arteries naturally lose elasticity. Stiff arteries that expand when the heart pumps have a harder time springing back between beats, which can actually cause the bottom number to drop while the top number stays high or rises. This is why older adults sometimes have a wide gap between their two numbers.
Blood Pressure Categories by Diastolic Number
The American Heart Association and American College of Cardiology classify blood pressure into clear ranges based on both numbers. Here’s where the bottom number falls in each category:
- Normal: below 80 mm Hg (with a top number below 120)
- Elevated: still below 80, but the top number sits between 120 and 129
- Stage 1 high blood pressure: 80 to 89 mm Hg
- Stage 2 high blood pressure: 90 mm Hg or higher
- Hypertensive crisis: 120 mm Hg or higher, which requires immediate medical attention
If your top number and bottom number fall into different categories, the higher category applies. So a reading of 135/78 would be Stage 1 high blood pressure because of the top number, even though the bottom number looks fine.
European guidelines use a slightly different threshold, defining hypertension as 140/90 mm Hg or higher and considering anything below 70 on the bottom as “nonelevated.” The U.S. guidelines are more aggressive, flagging problems earlier at 80.
When the Bottom Number Is Too High
A consistently elevated bottom number, even when the top number is normal, is called isolated diastolic hypertension. It typically doesn’t cause noticeable symptoms, but it raises your long-term risk of heart attack, heart failure, and death from cardiovascular disease. These risks are greatest for women and people under 60.
A bottom number between 80 and 89 puts you in Stage 1. At this level, lifestyle changes are usually the first step. Once it reaches 90 or above, you’re in Stage 2, where medication often becomes part of the conversation. A diastolic reading of 120 or higher is a hypertensive crisis. If you see that number along with symptoms like chest pain, headache, or vision changes, call 911.
When the Bottom Number Is Too Low
Low blood pressure is generally defined as a reading below 90/60 mm Hg, so a bottom number consistently under 60 may signal a problem. Symptoms of low diastolic pressure include dizziness, lightheadedness, blurred vision, fatigue, and trouble concentrating.
This is especially relevant for older adults. Research published in the AHA journal Hypertension found that in frail elderly patients with cardiovascular disease, a diastolic pressure at or below 60 mm Hg was associated with higher mortality, independent of other heart function measures. The same study identified 70 mm Hg as an optimal diastolic target for older adults with isolated systolic hypertension. Both the lowest and highest diastolic readings in the study group carried greater risk of death compared to those in the middle range (around 70 to 75). In short, the bottom number can be too low, not just too high.
Lifestyle Changes That Lower Diastolic Pressure
If your bottom number is creeping up, several proven strategies can bring it down. The most effective is improving your diet. Eating a pattern rich in whole grains, fruits, vegetables, and low-fat dairy while cutting saturated fat can lower blood pressure by up to 11 mm Hg. Reducing sodium to 1,500 mg per day (roughly two-thirds of a teaspoon of table salt) can drop it another 5 to 6 mm Hg.
Regular aerobic exercise, such as brisk walking, cycling, or swimming, lowers blood pressure by about 5 to 8 mm Hg. You don’t need intense workouts; consistency matters more than intensity. Weight loss helps too. Blood pressure drops by roughly 1 mm Hg for every kilogram (about 2.2 pounds) lost. Increasing potassium intake to 3,500 to 5,000 mg per day through foods like bananas, potatoes, and beans can add another 4 to 5 mm Hg reduction.
These effects are additive. Combining dietary changes with exercise, sodium reduction, and modest weight loss can produce meaningful drops in both numbers without medication.
Getting an Accurate Reading
Before worrying about your numbers, make sure you’re measuring correctly. Common mistakes can inflate your reading by 10 to 20 mm Hg or more, enough to push a normal result into the high range.
The biggest culprits: using a cuff that’s too small for your arm (which can add 5 to 20 mm Hg), skipping the five-minute rest period before measuring (another 10 to 20 mm Hg), talking or texting during the reading (10 to 15 mm Hg), and crossing your legs or letting them dangle off an exam table (5 to 8 mm Hg). A full bladder adds 10 to 15 mm Hg, and coffee within 30 minutes of measuring adds 5 to 8 mm Hg. Measuring over clothing can swing results by as much as 50 mm Hg in either direction.
For the most reliable reading, sit in a chair with your feet flat on the floor, rest quietly for five minutes, use a properly sized cuff on bare skin, and keep your arm supported at heart level. Take two or three readings a minute apart and average them. A single high reading doesn’t mean you have high blood pressure. The diagnosis is based on consistently elevated numbers across multiple visits or a pattern of high readings at home over days or weeks.