Your heart rate can tell you a lot about your fitness and cardiovascular health.

Your heart beats consistently, day in and day out, but you may not generally pay close attention to it. You might take note if you’re nervous, stressed, or if you sprint to catch the bus, but it’s a wise choice to check your heart rate on a regular basis, both at rest and during exercise.

“Heart rates can be a reflection of your heart health and even overall health,” says Owais Idris, MD, an interventional cardiologist at Texas Health Hospital Frisco in Frisco, Texas.

Your resting heart rate is the speed at which your heart beats when you’re not physically active. It’s typically measured in beats per minute (bpm). A healthy range for most adults is between 60 and 100 bpm. Usually, a resting heart rate on the lower end is a sign of better physical fitness, although some well-trained athletes may even have resting heart rates in the 40s.

“The stronger [the heart] is, the lower the heart rate needs to be in order to achieve the same amount of blood flow,” explains Brian Becerra, MD, a board-certified cardiologist at UC Irvine Medical Center in Orange, California.

Your fitness level isn’t the only thing that influences your resting heart rate. Your age, size, smoking, medication use, and other health conditions like heart disease or high cholesterol also factor in. Things like the air temperature, your body position, and emotions like stress or anxiety can have a temporary impact, too. Your heart will beat a little slower when you’re calm and lying down than when you’re on edge and standing up.

Heart rates that are too high or low may be a sign of an underlying problem like heart disease, lung disease, anemia, or an over- or underactive thyroid, says Christopher Kelly, MD, a cardiologist with UNC Health in Raleigh, North Carolina.

To get a sense of what’s normal for you, check your resting heart rate a few times a week, with a heart rate monitor, smartwatch, or a fitness tracker. If you don’t use wearable technology, you can perform a manual heart rate check. Lightly place your first two fingers on your pulse inside your wrist, count your pulse for 30 seconds, and multiply that number by two to calculate your bpm.Your maximum heart rate (MHR) is when you’re working your hardest during intense exercise and can’t push yourself any further. Your MHR number is estimated by subtracting your age from 220. At age 20, a person’s MHR is around 200 bpm, and by age 70, it drops to around 150 bpm.Dr. Idris says, ideally, this number should not be exceeded. But that equation is just an estimate, and it can be normal for your MHR to be 15 to 20 beats higher or lower than what’s typical for your age.

“If you start to feel dizzy or exhausted at a lower number, then you probably have a lower MHR than what is predicted [by the calculation],” Dr. Becerra adds. On the flip side, if you’re working out at your MHR and not yet at max effort, talk to your doctor about the possibility of upping that number.

Becerra says keeping tabs on your heart rate while you exercise is a great way to gauge intensity. During most forms of routine exercise, your target heart rate should be between 50 percent and 85 percent of your MHR.

During very intense exercise, such as during high-intensity interval training, competitive team sports, or powerlifting, your heart rate may exceed 85 percent of your MHR, although it’s almost impossible to keep up that pace for long.

If you have serious athletic goals, you may also choose to target specific heart rate zones during different types of training, depending on your individual goals and fitness level. Here’s how it breaks down.

• Zone 1 is 50–60 percent of your MHR. It’s appropriate for very easy workouts, warm-ups, and cooldowns. It’s also a good place to start if you’re new to exercise.

• Zone 2 is 60–70 percent of your MHR. It counts as moderate intensity exercise, which can help you build endurance and burn fat.

• Zone 3 is 70–80 percent of your MHR. It veers into vigorous intensity exercise territory, which can help you improve your fitness or get stronger.

• Zone 4 is 80–90 percent of your MHR. This is very vigorous exercise when you’re serious about increasing your speed.

• Zone 5 is 90–100 percent of your MHR. It’s a super-intense pace that’s mainly for athletes in competition.

It’s normal for your resting heart rate to vary throughout the day, so don’t be concerned if the number changes a bit from one reading to the next. If it’s a more dramatic change, it could be a sign of an underlying health problem. If your heart rate is above 100 bpm when you’re at rest, or if it’s below 60 bpm, let your doctor know.Call 911 if your heart rate suddenly changes and is accompanied by chest pain, shortness of breath, dizziness, or fainting.

• A normal resting heart rate for most adults is 60–100 bpm, with lower rates generally indicating better fitness. Factors like age, medications, and stress also help determine your resting heart rate.

• Maximum heart rate (MHR) determines how intensely you can exercise safely. It’s calculated by subtracting your age from 220. During moderate exercise, aim for 50–85 percent of your MHR, depending on your fitness level and goals.

• If you notice irregularities in your heart rate, speak to your doctor. You should seek immediate medical care if these changes are accompanied by sudden chest pain, shortness of breath, dizziness, or fainting.