Low blood pressure readings: what counts as low and what to write down
Below 90/60 is the line both the NHS and the American Heart Association use for low blood pressure. On its own a low reading is usually not a problem; what changes that is how you feel. So the thing to write down is the symptom and its time, next to the number.
What counts as low
The NHS states it directly: “low blood pressure is a reading of less than 90/60mmHg. It does not always cause symptoms, but you may need treatment if it does.” The American Heart Association draws the same line at less than 90/60 and adds that low blood pressure “is usually not harmful unless there are other concerning symptoms”.
There is no week-long protocol to confirm a low reading the way there is for a high one, because the symptoms carry the meaning rather than the average. The blood pressure calculator on this site classifies the high end only: anything below 120/70 comes back as the normal range, so 90/60 is the line to compare a low reading against yourself.
A low number with no symptoms
Usually good news. In the AHA’s words, “a low blood pressure reading is usually good”, and “one reading that is lower than normal is usually not cause for alarm unless you are having other symptoms or problems”.
It is also not a reason to stop measuring. Keep the routine, keep the row, and let the pattern show. The average blood pressure calculator will tell you whether last week really was lower than the week before, which is a better question than what one morning showed.
The symptoms that change the picture
The NHS asks you to get your blood pressure checked if you keep getting lightheadedness or dizziness, feeling sick, blurred vision, generally feeling weak, confusion or fainting.
The AHA’s instruction for the moment itself is short: if you are dizzy, nauseous or have other symptoms, contact your healthcare professional, and keep a record of your symptoms and when they happened. Sit or lie down first. A reading taken while you feel faint is worth having, but not worth standing up for.
Standing up: postural hypotension
If the symptoms arrive when you stand or change position suddenly, the NHS names the pattern: postural hypotension.
There is a measurement for it, and it is not the one you do at the table. NICE NG136 has the clinician measure blood pressure with the person lying on their back, then again after at least one minute of standing. A fall of 20 mmHg or more in the top number, or 10 mmHg or more in the bottom number, is what they are looking for. Expect that sequence at the appointment if you describe dizziness on standing.
Between now and then, the NHS advice is practical: get up slowly from sitting to standing, and move slowly from lying to sitting to standing when getting out of bed.
What to write down
The reading, the time, what you were doing, and the symptom itself. A row that says 86/54, 7:40, stood up from bed, dizzy for a minute tells a doctor something that 86/54 alone does not.
The printable blood pressure log has a notes column for exactly that; how to keep a blood pressure log covers the rest of the week. BP Diary keeps the note with the reading and its time, so the symptom and the number stay together in the report your doctor reads.
When to see a doctor
The NHS line is repetition: see a doctor if you keep getting symptoms of low blood pressure such as dizziness and fainting. A single low reading with no symptoms can simply be logged; a pattern of dizziness, faintness or confusion is a reason to make the appointment, and to bring the log with the symptoms written in it.