Blood Pressure Calculator

Under the 2017 ACC/AHA guideline, an adult reading counts as normal only when both numbers sit under the line: systolic pressure below 120 mmHg and diastolic pressure below 80 mmHg. When systolic floats between 120 and 129 while diastolic stays under 80, the stage is called Elevated, an early warning rather than a diagnosis. At 130/80 or above the guideline says Stage 1, and it judges by the higher of the two categories when the numbers disagree, so 128/84 is Stage 1 even though the systolic value is still below 130. From 140/90 upward the reading is Stage 2, and a single measurement above 180 systolic or 120 diastolic is a hypertensive crisis, a level that calls for a calm recheck and, if it repeats or symptoms appear, medical help the same day.

Blood pressure moves. Between the tension of a strap going tight, the morning coffee, the stairs you ran up and the ordinary nervousness of a medical setting, a single reading can swing 10 mmHg or more in either direction, which is exactly the distance between one category and the next. Guidelines therefore build the average into the diagnosis itself: they ask for readings taken a minute apart and use their mean to decide, so that moment-to-moment noise cancels out instead of deciding whether you leave the office with a prescription. A calculator that averages a whole batch the same way gives you the same protection at home, where there is no white coat to blame for the spike.

Many clinics do skip the first number, and the reasoning is practical rather than mysterious: the first measurement arrives on a person who may have sat down seconds ago, is often still a little tense, and tends to land higher than the readings taken after the arm has settled. Dropping it nudges the average toward the resting state the definition is actually about. Studies find the effect real but modest, which is why the habit is convention as much as law, and why the calculator makes it a checkbox: tick it to follow the common clinic practice, leave it off when your own readings already started from a calm sit. Either way, keep at least two readings in the average, never fewer.

MAP is the average pressure your arteries hold across one full heartbeat, and it matters because organs such as the kidneys and the brain are fed by that average, not by the two peaks your cuff reports. The calculator derives it from the same two numbers you entered, using MAP = diastolic + (systolic - diastolic) / 3; the one-third weighting reflects that the heart spends roughly a third of the cycle contracting and two-thirds resting. For a healthy adult, roughly 70 to 100 mmHg keeps the organs supplied, and a MAP below about 60 suggests the pressure is running too low to keep them comfortable even when the systolic number itself looks unremarkable. Like every value on this page, one unusual MAP deserves a recheck, not a diagnosis.

Pulse pressure is simply the systolic number minus the diastolic one, and in healthy adults it commonly sits near 40 mmHg: 120 over 80 gives 40, and so does 110 over 70. It widens as arteries stiffen with age or when the aortic valve leaks blood back into the heart, and it narrows when blood volume drops, for instance through dehydration or bleeding. How wide or narrow your own runs varies with the person, which is why no calculator should turn one pulse pressure reading into a verdict. The value earns its slot on this page because it describes the width of one heartbeat, a nudge that the two cuff numbers belong to the same pulse, and because doctors do glance at it, particularly in older patients whose systolic readings run very high.

For adults aged 18 and over, the 2017 ACC/AHA categories are deliberately age-blind: 120/80 carries the same meaning at 25 and at 75, exactly as this calculator applies them. Two groups sit outside that frame. Children and teenagers are judged against percentile charts that weigh age, sex and height together, so a fixed 120/80 line would mislabel most of them. In pregnancy, thresholds and escalation rules bend to their own protocol, because a reading of 140/90 after week 20 is treated as a warning sign rather than an average Tuesday. Leave the age field empty and you get the standard adult stage; enter an age under 18 and the calculator declines politely and points toward a pediatrician.

No, and the refusal is the honest answer rather than a missing feature. A child's reading is interpreted against percentile charts that fold together age, sex and height, so the number that is unremarkable for a tall 12-year-old can be a flag for a small 8-year-old, and those charts live in pediatric practice tools, not in a browser tab. Pregnancy redefines the thresholds too: after the twentieth week, a 140/90 reading belongs on the watchlist for preeclampsia, and the rules for what happens next are different from the adult standard. For anyone in either group, the correct calculator is the one your midwife, obstetrician or pediatrician runs, and the right next step is to bring the cuff log to them.

Nothing leaves your device. The calculator keeps saved readings in your browser's localStorage, the same private storage a shopping cart uses to remember its contents between visits, and the only person who can read them back is whoever uses this browser on this computer. Clearing the browser's site data removes them, private-mode tabs keep nothing at all, and no account, upload or API call is ever involved. If your doctor wants the record, the CSV export writes a plain spreadsheet file of the dates and values you saved, and that file is yours alone once it downloads. Delete a row one by one or wipe the whole log with the Delete All button, both of which act immediately.

Three situations call for a same-day conversation with a professional rather than more self-assessment. First, a reading above 180 systolic or 120 diastolic, especially when a calm recheck a minute or two later repeats it, is a hypertensive crisis by the guideline's own definition, with or without symptoms. Second, a high reading followed by chest pain or pressure, shortness of breath, a sudden severe headache, blurred or lost vision, one-sided weakness or numbness, or trouble speaking needs urgent medical attention, not a calculator. Third, symptoms of pressure that is running too low, such as fainting, near-fainting or persistent light-headedness, belong in front of a doctor even when the cuff numbers look ordinary. This page does the arithmetic; it does not stand in for the clinician who reads your full history.