You can feel your heart race and sometimes sense when it’s beating extra fast. But according to Ian del Conde Pozzi, MD, a cardiologist at Miami Cardiac & Vascular Institute, high blood pressure typically has no symptoms. “A person may feel perfectly fine yet have dangerously elevated blood pressure. The only way to know that one’s blood pressure is normal is by measuring it,” says Dr. del Conde. This is why he recommends all adults regularly monitor their blood pressure at home.

While your pulse is the rate at which your heart is beating, blood pressure refers to the force of blood pushing against the walls of your arteries, explains Dr. del Conde. (Think about a hose in the summertime, and how bending it slows the water flow.) This force is essential for circulating oxygen and other nutrients throughout your body. So when your blood pressure is consistently too high or too low, it can have serious health consequences.

High blood pressure, known as hypertension, can make your heart overwork and can push too hard on your arterial walls, according to the Mayo Clinic. Over time, this can damage your arteries and increase your risk of heart disease, stroke, and kidney failure. Low blood pressure, or hypotension, on the other hand, can cause dizziness, fainting, nausea, and confusion.

Staying informed about your blood pressure will give you a chance to take action to maintain healthy levels (and incorporate lifestyle changes like eating less salt and reducing alcohol intake for high blood pressure). And testing at home can be particularly helpful because some patients become nervous at the doctor’s office, which can cause briefly elevated “white coat hypertension” when, in fact, their blood pressure is normal during regular activities, says Ronald Grifka, MD, a cardiologist and chief medical officer with the University of Michigan Health-West.

How often to take your blood pressure—and what to look for

Dr. del Conde suggests that adults with regularly normal blood pressure readings take their blood pressure at home once a month, and those with high blood pressure that’s not under control should take a reading once a day.

“If someone notices that the blood pressure consistently approaches or exceeds 140/90 mm Hg, they should contact their physician for further evaluation and possible treatment,” says Dr. del Conde.

Those numbers refer to your systolic (the top one) and diastolic (the bottom) blood pressure. Systolic pressure is the force of blood against your arteries when your heart contracts, while diastolic is the force when your heart is resting between beats. According to the Mayo Clinic, a healthy blood pressure reading is typically around 120/80.

As important as it is to stay on top of these numbers, the reality is that most of us aren’t trained medical assistants. So there are a number of pitfalls that can happen when we’re measuring our own blood pressure.

The 9 most common mistakes when people take their blood pressure at home

1. Testing it with a full bladder

Believe it or not, having to go to the bathroom can affect your blood pressure. Without getting too technical, a full bladder causes the kidneys to respond in a certain way which changes your blood pressure. Going to the bathroom 20 to 30 minutes beforehand will get you a more accurate reading.

2. Crossing your legs and not sitting up straight

When you’re taking your blood pressure at home, you should be sitting upright with the machine on a flat surface. A kitchen or dining room table is ideal, with your feet on the floor and your arm supported at heart level (ideally resting on the table or an arm of your chair).

Crossing your legs while taking your blood pressure can give you a falsely high reading, according to the Mayo Clinic, because you could be compressing the arteries in your legs and restricting blood flow.

3. Taking your blood pressure over your clothing

Nurses and medical assistants have you take your sleeve off your arm when taking your blood pressure for a reason: It’s best for getting the most accurate reading. Taking your blood pressure over layers of clothing can cause you to have a lower, less accurate reading, according to Dr. del Conde.

4. Not using the right sized cuff

“One of the most important factors when measuring blood pressure is using the correct size cuff,” says Dr. Grifka. “If the cuff is too large, the measured blood pressure is usually falsely decreased.” Conversely, if the cuff is too small, the measured blood pressure is often falsely elevated.

The width of the cuff should be able to wrap three-quarters of the distance around the arm. Your cuff should be snug but not tight or cutting off your circulation, says Dr. Grifka. Each blood pressure monitoring device is different, so make sure you read the instructions carefully.

If you’re not sure whether the size is right—or how to best use it—bring your monitor to your next doctor’s appointment and ask for an assessment.

5. Using devices that use the wrist or finger

Machines that measure blood pressure at the wrist or finger are far less accurate. It’s best to use an analog cuff that inflates manually or an electronic machine that measures your blood pressure on your upper arm.

6. Not taking your blood pressure at the same time

“If you measure your blood pressure correctly, you only need to do it one time each day and try to do it the same time every day,” says Dr. Grifka. When collecting a data set on your body, it’s best to have as many variables controlled as possible, including time of day.

However, it may be helpful to measure your blood pressure twice in a row, trying it again one minute after the first measurement; this will allow you to average the two readings. If there is a discrepancy between the two, wait another minute and check it a third time.

7. Drinking caffeine, smoking, or exercising too close to your reading

“You need to be at rest for five minutes before measuring your blood pressure. Don’t exercise, smoke, or have any caffeine for 30 minutes before measuring your blood pressure,” says Dr. Grifka. You should be calm, silent, and sitting upright.

8. Using an inaccurate device

There can be discrepancies between the home units and office units, so making sure the numbers are consistent on both devices is important to guide treatment, says Dr. Grifka. The machine at a medical office is more likely to be correct, so bring yours to your next appointment to check that the readings match.

9. Not writing down the numbers you get

Last but certainly not least, always record your numbers somewhere you can find them later on. Whether that means writing it in a phone note or notebook, make sure you have a way to access that data months or years down the road. You never know when you might need a reliable data set to compare to.