Blood pressure calculator: read your systolic and diastolic numbers and see your AHA category, from normal to hypertensive crisis. Free, runs in your browser.
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These tools provide general estimates for planning and education only.
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A worked example: why both 132/84 and 128/84 are Stage 1
Take a reading of 132/84. The calculator checks systolic first against the crisis threshold: 132 is below 180. Next, Stage 2: 132 is below 140, and 84 is below 90, so no match. Stage 1 fires next: the rule is systolic of 130 or more OR diastolic of 80 or more. Here both are true (132 >= 130 and 84 >= 80), so the category is Stage 1 hypertension. Because the OR logic short-circuits, only one number needs to cross its line.
Now drop the systolic to 128 and keep 84. Stage 2 still fails (128 < 140, 84 < 90). Stage 1: 128 is under 130, but the diastolic leg saves it because 84 >= 80, so it is still Stage 1. Drop to 122/74: 122 is under 120's crisis check, under 140, under 130, and 74 is under 80, so it falls to the Elevated band, which starts at a systolic of 120. Only at 119/74 does it classify as Normal.
The practical takeaway is that the diastolic carries you across thresholds you would otherwise miss. A person at 118/82 is Stage 1 even though their systolic looks fine on its own. That is why clinics treat the higher-risk of the two numbers, and why this calculator uses OR rather than averaging the two readings together.
Where single-reading classification breaks down
A cuff reading varies by 5 to 10 mmHg between arm positions and by more across the day. Reading 134/86 after coffee and 126/82 the next morning are both Stage 1 on this calculator, but a 7-day average of 20 readings might land near 128/83, right at the band edge. Clinical guidelines use the average of at least 2 readings on 2 separate occasions before diagnosing hypertension, so treat one classification as a flag, not a verdict.
Device and body factors shift numbers too. A cuff that is too small (under about 80 percent of upper-arm circumference) can overstate systolic by 10 mmHg or more, which is enough to move 128 into the Stage 1 band falsely. White-coat effect adds roughly 10 to 20 mmHg for some people in clinical settings, which is why home readings matter. Conversely, an irregular heartbeat from atrial fibrillation can make automated oscillometric cuffs read unreliably low or error out entirely.
The calculator also classifies anyone at 180/120 or above as a crisis case with no symptoms input, and it cannot see pregnancy, kidney disease, or diabetes, where clinics use lower treatment thresholds (often 130/80 with confirmation). If your readings sit within 5 mmHg of a band boundary, log a week of seated morning readings and take the average to that clinician conversation instead of one number.
