Blood pressure measured once in a doctor's office tells an incomplete story. According to the WHO (2023), hypertension affects 1.28 billion adults worldwide — yet nearly half are unaware they have it. 'White coat hypertension' — blood pressure that spikes only in medical settings — affects a further 15–30% of people diagnosed in clinic. Home monitoring, done consistently, gives a far more accurate picture of what your cardiovascular system is actually doing day to day.
This guide explains how to measure correctly, what the categories mean, how to spot dangerous trends early, and when to call a doctor.
Understanding the two numbers
Blood pressure is recorded as two figures: systolic over diastolic, measured in millimetres of mercury (mmHg). The top number (systolic) is the pressure when your heart beats and pushes blood out. The bottom number (diastolic) is the pressure between beats, when the heart is at rest.
Both numbers matter. You can have normal systolic pressure with elevated diastolic, or vice versa. Either pattern carries risk.
- **Normal:** below 120/80 mmHg
- **Elevated:** 120–129 / below 80 mmHg — not yet hypertension, but trending in the wrong direction
- **Stage 1 hypertension:** 130–139 / 80–89 mmHg — lifestyle changes and monitoring recommended
- **Stage 2 hypertension:** 140/90 mmHg or higher — medication often needed alongside lifestyle changes
- **Hypertensive crisis:** above 180/120 mmHg — seek medical attention immediately, especially if you have symptoms
How to measure accurately at home
The technique matters as much as the device. Small errors in method produce readings that are off by 10–15 mmHg — enough to change your clinical category entirely.
- Sit quietly for five minutes before measuring. Don't measure after exercise, caffeine or a meal.
- Sit with your back supported, feet flat on the floor, and the cuff at heart level.
- Use a validated upper-arm cuff — wrist monitors are less accurate.
- Take two readings, one minute apart, and record the average.
- Measure at the same time each day — morning before medications and evening before bed are the standard recommendation.
- Don't talk during the measurement.
What to look for over time
A single reading tells you very little. What matters is the pattern across dozens of readings over weeks and months. Look for:
- A gradual upward trend, even if individual readings stay within range
- Consistently elevated morning readings, which can indicate poor overnight control
- High variability between readings — blood pressure that swings widely is independently associated with cardiovascular risk
- The effect of lifestyle changes — reduced sodium, increased exercise, weight loss — on your average
Factors that affect your reading
Blood pressure is not a fixed number. It changes constantly in response to your circumstances. Knowing what moves it helps you interpret your log correctly.
- **Sleep** — poor sleep reliably raises blood pressure, often into the next day
- **Stress and anxiety** — acute stress can push readings 20–30 mmHg above baseline
- **Sodium intake** — excess salt causes fluid retention and raises systolic pressure in salt-sensitive individuals
- **Alcohol** — even moderate intake elevates blood pressure the morning after
- **Medications** — decongestants, NSAIDs and some antidepressants can all raise blood pressure
- **Hydration** — mild dehydration increases it; some medications cause it to drop
Keeping a log that's actually useful
A notebook works, but it makes trends difficult to see and easy to lose. Looms' Vitals Journal lets you log blood pressure readings alongside other vitals — heart rate, blood glucose, weight — and automatically charts trends over time with normal range reference lines. You can share a 90-day summary with your doctor in seconds, giving them the full picture rather than a single clinic measurement.
When to call your doctor
- A reading above 180/120 mmHg, especially with headache, chest pain, vision changes or shortness of breath — this is a medical emergency
- Consistently elevated readings over two weeks, even if none are critically high
- A sudden significant rise from your established baseline
- Low readings accompanied by dizziness, fainting or weakness — low blood pressure can be equally dangerous