Blood Pressure Calculator

The 2017 ACC/AHA guideline lowered the threshold for hypertension from 140/90 to 130/80. Nobody's blood pressure changed; the label did. A reading of 135/85 was "prehypertension" under the older JNC7 framework and is stage 1 hypertension now.

The change roughly doubled the share of US adults classified as hypertensive, which drew criticism. The reasoning was that cardiovascular risk rises continuously from about 115/75 upward, with no natural breakpoint, and that intervening earlier — mostly through lifestyle rather than drugs — prevents more events than waiting.

Importantly, the lower threshold did not mean medication for everyone above it. At stage 1, whether drugs are recommended depends on overall cardiovascular risk, not the reading alone.

The categories are not symmetrical, and this trips people up constantly. Normal and elevated require *both* numbers to be in range. The hypertension stages require only *one*.

So 128/92 is stage 2 hypertension. The systolic number looks nearly fine, and someone scanning a chart along the top row would call it elevated. But a diastolic of 92 is on its own enough for stage 2, and when the two numbers fall in different categories, the higher one governs.

The reverse happens too: 145/78 is stage 2 on the systolic figure alone, despite a diastolic that is entirely normal. Isolated systolic hypertension of this kind is the most common pattern after about 60, as arteries stiffen.

Blood pressure is not a fixed property. It follows a daily rhythm, dipping at night and peaking mid-morning, and it responds within seconds to stress, pain, caffeine, nicotine, a full bladder, talking, and crossed legs. The act of being measured by a clinician raises it in a substantial minority of people — white coat hypertension — and a smaller group shows the opposite, with normal clinic readings masking genuine hypertension at home.

Diagnosis therefore requires repeated measurements on separate occasions, and increasingly home or 24-hour ambulatory monitoring rather than clinic readings alone. Technique matters as much as repetition: seated with back supported, feet flat, arm at heart level, correctly sized cuff on a bare upper arm, after five minutes of quiet rest, with no talking during the measurement. A cuff that is too small reads high, sometimes by 10 to 20 mmHg.

Pulse pressure is the gap between the two numbers. It widens with age as the large arteries stiffen and lose the elastic recoil that used to cushion each ejection of blood. A pulse pressure above about 60 mmHg in an older adult carries cardiovascular risk information over and above either number alone.

Mean arterial pressure is the average pressure perfusing your organs across the whole cardiac cycle. It is not the midpoint of the two numbers: at rest the heart spends roughly two thirds of each cycle relaxed, so diastolic pressure is weighted twice as heavily. That is where the formula DBP + (SBP − DBP) ÷ 3 comes from. It matters clinically because organ perfusion depends on MAP, and the approximation degrades at high heart rates where diastole shortens.