A healthy diastolic blood pressure is below 80 mmHg. That’s the bottom number in a blood pressure reading, and it reflects the pressure inside your arteries between heartbeats, when your heart is resting and refilling with blood. Once that number reaches 80 or higher, it falls into the hypertension range, even if the top number looks fine.
Diastolic Pressure Ranges for Adults
The American Heart Association breaks diastolic blood pressure into four categories:
- Normal: below 80 mmHg
- Elevated blood pressure: below 80 mmHg (with a systolic reading between 120 and 129)
- Stage 1 hypertension: 80 to 89 mmHg
- Stage 2 hypertension: 90 mmHg or higher
Notice that in the “elevated” category, the diastolic number is still normal. That category exists to flag people whose top number is creeping up. So if your diastolic reading is between 80 and 89 while your systolic is under 130, you’re in stage 1 hypertension territory based on the bottom number alone. These thresholds apply to all adults regardless of age. Current guidelines do not set a different diastolic target for people over 65.
What Diastolic Pressure Actually Measures
Your heart works in a squeeze-and-relax cycle. The systolic number (the top one) captures the peak pressure when the heart contracts and pushes blood out. The diastolic number captures the lowest pressure in your arteries, which occurs while the heart muscle relaxes and its chambers refill. During this phase, the valve between the heart and the main artery snaps shut, and the heart generates a kind of gentle suction that draws blood back in from the veins. About 90% of heart filling happens passively this way, with a final small squeeze from the upper chambers contributing the last 10%.
Because diastolic pressure reflects what’s happening in your arteries at rest, a high reading suggests the blood vessels aren’t relaxing as well as they should. That persistent tension forces the heart to work harder even during its “off” moments.
When Only the Bottom Number Is High
A condition called isolated diastolic hypertension occurs when your bottom number hits 80 or higher while your top number stays below 130. It’s diagnosed after two or more office visits show the same pattern. This tends to be more common in younger adults, whose arteries are still elastic enough to keep systolic pressure in check even as other factors push diastolic pressure up.
It may not feel urgent, but the long-term risks are real. Isolated diastolic hypertension raises your lifetime risk of heart attack, increases the chance of dying from cardiovascular disease, and makes congestive heart failure more likely. Because there are no obvious symptoms, the only way to catch it is through regular blood pressure checks.
When Diastolic Pressure Is Too Low
Low blood pressure is generally defined as a reading below 90/60 mmHg. So a diastolic number below 60 is on the low side, but most doctors only consider it a problem if it’s causing symptoms. Those symptoms include dizziness or lightheadedness, blurred or fading vision, fainting, fatigue, difficulty concentrating, and nausea.
Some people naturally run low and feel perfectly fine. Others develop low diastolic pressure from dehydration, blood loss, certain medications, or heart conditions that reduce the heart’s pumping efficiency. If you’re consistently reading below 60 on the bottom number and experiencing any of those symptoms, that’s worth investigating.
Normal Ranges for Children and Teens
Children’s blood pressure is evaluated differently than adults’. Instead of fixed cutoffs, doctors compare a child’s reading to other kids of the same age, sex, and height using percentile charts. A reading at or above the 95th percentile on repeated visits is considered hypertension.
To give you a rough sense of what’s typical, here are the 50th percentile (average) diastolic values at a few ages for average-height children:
- Age 1: about 37 mmHg for boys, 40 for girls
- Age 5: about 53 mmHg for boys, 54 for girls
- Age 10: about 61 mmHg for boys, 60 for girls
- Age 17: about 67 mmHg for boys, 66 for girls
By the late teen years, these values approach adult ranges, and the adult threshold of 80 mmHg starts to apply.
Getting an Accurate Reading
Blood pressure is surprisingly easy to measure incorrectly, and the errors can be large enough to change your diagnosis. A few common mistakes and how much they can skew results:
- Full bladder: can inflate the systolic reading by up to 33 mmHg
- Wrong arm position: having your arm lower than heart level can add 4 to 23 mmHg to the reading
- Wrong cuff size: a cuff that’s too small or too large will give inaccurate numbers in either direction
- White coat effect: the anxiety of being in a medical setting can push readings up by as much as 26 mmHg, and studies show readings taken by doctors tend to be higher than those taken by nurses
For the most accurate result, sit quietly for five minutes before the reading. Keep your feet flat on the floor, your back supported, and your arm resting on a flat surface at heart level. Don’t talk during the measurement. If you’re monitoring at home, take two readings a minute apart and average them. Home readings over several days give a much clearer picture than a single office visit.
Lowering Diastolic Pressure Through Lifestyle
If your diastolic number is running in the 80s, lifestyle changes alone can often bring it back below 80. Two of the most effective dietary adjustments involve sodium and potassium.
Cutting sodium to 1,500 mg per day (about two-thirds of a teaspoon of table salt) can lower blood pressure by roughly 5 to 6 mmHg. Most of the sodium in a typical diet comes from processed and restaurant foods rather than the salt shaker, so reading labels and cooking more meals at home makes the biggest difference.
Increasing potassium intake to 3,500 to 5,000 mg per day can lower blood pressure by another 4 to 5 mmHg. Potassium helps your body flush out excess sodium through urine. Good sources include bananas, potatoes, spinach, beans, yogurt, and avocados. For someone whose diastolic reading is sitting at 84 or 85, combining these two changes could be enough to move the number back into the normal range without medication.
Regular aerobic exercise, maintaining a healthy weight, limiting alcohol, and managing stress all contribute as well. These aren’t small effects. In combination, lifestyle changes can rival what a single blood pressure medication achieves.