Blood Pressure Category Calculator

The five categories, and where the lines fall

The categories used here come from the 2017 guideline from the American College of Cardiology and the American Heart Association, which lowered the threshold for high blood pressure from 140/90 to 130/80. Five bands came out of that change, and each one is defined by a pair of numbers rather than a single figure.

The word that matters is the one between the columns. Normal and elevated require both numbers to be in range, because they are the absence of disease. Stage 1 and stage 2 use or, so a single high number is enough. That is the whole logic of the chart, and it is the part most people miss when they read a number like 118/84 and assume they are fine.

Nearly half of adults in the United States fall into one of the hypertension bands under these thresholds. The CDC fact sheet on high blood pressure puts it at 48.1%, or about 119.9 million adults, using data from 2017 to 2020.

The higher number decides the category

When the two numbers disagree, the higher category wins. A reading of 118/84 has a normal systolic and a stage 1 diastolic, so the reading is stage 1. A reading of 145/82 has a stage 2 systolic and a stage 1 diastolic, so the reading is stage 2.

This is not a technicality. Isolated diastolic hypertension is common in adults under 40, and isolated systolic hypertension is the most common pattern after 60, when the arteries stiffen and the top number climbs while the bottom one falls. Grading only the systolic, or only the diastolic, misses one of the two patterns.

The calculator shows which number set the result, because that tells you what to watch. If your diastolic keeps landing at 86 while the systolic stays near 118, the diastolic is the number to bring to your next appointment. If the pattern reverses, the systolic is the one to track.

Worked example: 138 over 86

Take the reading 138/86, which is the default in the calculator, and grade it the way the chart does.

• Systolic 138 falls in the 130 to 139 band, which is stage 1.
• Diastolic 86 falls in the 80 to 89 band, which is stage 1.
• Both numbers agree, so the reading is stage 1 high blood pressure.

Two extra numbers come out of the same reading. Pulse pressure is 138 minus 86, which is 52. Mean arterial pressure is 138 plus twice 86, divided by three, which is 103.3. Neither one changes the category, but both are useful context: a pulse pressure in the 40s is typical, and a mean arterial pressure between 70 and 100 is the usual resting range.

Now move one number at a time and watch the category move. Drop the systolic to 128 and the reading is 128/86, still stage 1 because of the diastolic. Drop both to 118/76 and it is normal. Raise the systolic to 152 and it is stage 2, even if the diastolic stays at 86.

The same reading also explains why a home average matters. One 138/86 is a data point. Five mornings of readings that average 138/86 is a pattern, and the pattern is what a clinician treats.

How to take a home reading that counts

A home monitor is only as good as the routine around it. The steps below are the ones the AHA recommends, and skipping them can move a reading by 10 to 20 mm Hg.

• Sit quietly for 5 minutes before the first reading.
• Feet flat on the floor, back supported, arm supported at heart level.
• Cuff on bare skin, sized to your arm. A cuff that is too small reads high.
• No caffeine, exercise or smoking for 30 minutes before, and empty your bladder first.
• Do not talk during the measurement.
• Take 2 readings, 1 minute apart, and average them.

Averaging is not a courtesy to the patient. A single reading carries the noise of the moment, and averaging two readings one minute apart removes much of it. The first example is the reason: 132/84 alone is stage 1, 128/80 alone is stage 1, and the average of 130/82 is stage 1 too, but a pair of 142/92 and 126/80 averages to 134/86 and tells a different story from either number on its own.

Keep a log with the date, time, both readings and the average. Three to seven days of morning and evening pairs is usually enough for a clinician to work with, and it beats a single number remembered from a rushed visit.

What the two numbers measure

Systolic pressure is the peak pressure in your arteries when the heart contracts. Diastolic pressure is the trough, measured between beats while the heart refills. Both are reported in millimeters of mercury, written mm Hg, which is a leftover from the mercury columns of the first instruments.

Systolic rises with age in most people, because large arteries stiffen and lose the ability to absorb the pulse. Diastolic tends to rise until about 50 and then flatten or fall. That is why a 70 year old can have 150/70 while a 35 year old has 118/88, and why both numbers have to be read against age and the rest of the picture.

Pulse pressure, the gap between them, is a rough signal of arterial stiffness. Around 40 is typical. A gap of 60 or more in an older adult is worth raising with a doctor, though it is not a diagnosis on its own.

Mean arterial pressure is the average pressure driving blood into the organs, and it weights the diastolic phase more heavily because the heart spends about twice as long filling as it does contracting. The formula is systolic plus twice diastolic, divided by three. The NHLBI high blood pressure page covers what the numbers mean for heart and kidney risk.

Above 180 over 120: the crisis line

The top band is different from the other four. A reading above 180 systolic or above 120 diastolic is a hypertensive crisis, and the AHA chart words it as higher than 180 and/or higher than 120. A reading of exactly 180/120 sits at the top of stage 2 under that wording, and it still deserves a call to a doctor the same day.

What you do next depends on symptoms. With chest pain, shortness of breath, back pain, numbness or weakness, a change in vision, or trouble speaking, call 911. That combination can mean organ damage, and minutes matter. Without symptoms, sit quietly for 5 minutes and take another reading. If it is still above 180/120, contact a doctor or an urgent care clinic right away rather than waiting for a scheduled visit.

Two things are worth knowing about extremely high readings. First, a single spike is common after heavy caffeine, a stressful event, or a missed dose of medication, and it usually settles. Second, a cuff that is too small or an arm held below heart level can add 10 to 15 mm Hg, so recheck the setup before you panic.

Nothing on this page is a diagnosis. The category is a reading of two numbers against a published chart, and the MedlinePlus guide to high blood pressure is a plain-language place to read more before your appointment.

What the category does not tell you

A category is a snapshot. It does not say how long the pressure has been high, whether the arteries are already damaged, or what your risk of a heart attack or stroke looks like. Two people with identical readings can get different advice because of age, diabetes, kidney function, pregnancy or existing heart disease.

It also does not capture the difference between clinic and home. White coat hypertension raises the number in a doctor's office and looks normal at home. Masked hypertension does the opposite, with a normal office reading and a high home average. Both are common, and both are reasons a home log is more useful than a single visit.

Finally, the chart is for adults. Children and teens are graded on age, sex and height percentiles, so a 12 year old with 118/76 is not read against the adult table at all. Pregnancy has its own thresholds as well.

Use the calculator to translate a reading into plain language and to see which number is driving the result. Then take the log to a clinician, who can put it next to everything else that matters.