A healthy heart rate during exercise falls between 50% and 85% of your maximum heart rate, depending on how hard you’re working. For moderate exercise like brisk walking, aim for 50% to 70% of your max. For vigorous exercise like running or cycling hard, the target is 70% to 85%. These ranges, recommended by the American Heart Association, are where your heart gets stronger without being pushed into unsafe territory.
How to Find Your Maximum Heart Rate
Your maximum heart rate is the ceiling your heart can sustain during all-out effort. The simplest way to estimate it is the classic formula: 220 minus your age. A 40-year-old would get a max of 180 beats per minute (bpm). That formula has been used for decades, but it tends to underestimate the true max for older adults.
A more refined version, developed by researcher Hirofumi Tanaka, calculates it as 208 minus 0.7 times your age. For that same 40-year-old, the result is 180 bpm (nearly identical at that age), but by age 65 the two formulas diverge meaningfully: the classic gives 155, while Tanaka’s gives 162. If you’re over 50, the Tanaka formula is likely closer to your actual max.
Both formulas are estimates. Your true maximum can vary by 10 to 15 bpm in either direction based on genetics and fitness. The only way to know it precisely is through a supervised exercise stress test.
What Each Intensity Zone Does for You
Once you know your estimated max, the math is straightforward. A 35-year-old with a max of about 185 bpm would target roughly 93 to 130 bpm for moderate exercise and 130 to 157 bpm for vigorous exercise. But these zones aren’t just numbers on a chart. They correspond to different things happening inside your body.
At the lower end (50% to 70%), you’re in what exercise physiologists call “Zone 2.” This is a conversational pace where you can talk in full sentences. Training here improves your cells’ ability to use oxygen efficiently, enhances fat metabolism, and increases insulin sensitivity. Your body gets better at burning fat as fuel, which supports endurance and body composition over time. This is the zone that makes up the bulk of training for most endurance athletes, and it’s increasingly recognized as one of the most valuable intensities for long-term metabolic health.
At the higher end (70% to 85%), you’re breathing hard and can only manage short phrases. This zone builds cardiovascular power, pushes your aerobic ceiling higher, and burns more calories per minute. Most people don’t need to spend the majority of their exercise time here, but regular doses of vigorous effort improve heart strength and oxygen delivery to muscles.
Going above 85% of your max puts you into near-maximal effort. Short bursts in this range (like sprint intervals) can be effective for trained individuals, but sustained time above 85% is unnecessary for general fitness and increases the risk of overexertion.
A More Personalized Calculation
The percentage-of-max method works as a starting point, but it ignores your resting heart rate, which reflects your current fitness level. Someone with a resting heart rate of 55 bpm and someone at 80 bpm will have very different experiences at the same target number.
The Karvonen formula accounts for this. It calculates your heart rate reserve (maximum heart rate minus resting heart rate), then applies the target percentage to that reserve, and adds your resting rate back in. For a 40-year-old with a max of 180 and a resting rate of 60, the heart rate reserve is 120. A 60% target would be (120 × 0.60) + 60 = 132 bpm, compared to 108 bpm using the simpler percentage-of-max method. The Karvonen formula tends to give more accurate zones, especially for people who are already fit and have lower resting heart rates.
To use it, measure your resting heart rate first thing in the morning before getting out of bed, averaged over a few days.
When Medications Change the Rules
Beta blockers, commonly prescribed for high blood pressure and certain heart conditions, slow the heart rate and prevent it from rising normally during exercise. If you take one, you may never reach your calculated target heart rate no matter how hard you push. Using a standard heart rate zone in this situation can lead you to overexert yourself trying to hit a number your heart simply can’t reach on the medication.
Instead of relying on heart rate, people on beta blockers can use a perceived exertion scale. The Borg Rating of Perceived Exertion asks you to rate your effort on a scale from 6 (no exertion) to 20 (maximal effort). Moderate exercise corresponds roughly to a 12 to 14, where you feel like you’re working but could keep going. This approach works for anyone whose heart rate response is blunted by medication, and an exercise stress test can help calibrate what “moderate” actually feels like for your situation.
How Accurate Is Your Watch?
Most people track their heart rate with a wrist-worn device. These are convenient, but their accuracy varies. In a study comparing popular devices against a medical-grade ECG, chest straps like the Polar H7 showed 98% agreement with the ECG reading. The Apple Watch came in at 96% agreement. Other wrist devices like the Fitbit Iconic and Garmin Vivosmart HR were lower, around 89%.
Accuracy drops further at higher speeds. At 8 to 9 mph on a treadmill, none of the wrist-worn devices tested maintained reliable readings. The motion of your arms disrupts the optical sensor’s ability to track blood flow. Some devices also showed consistent biases: the TomTom Spark 3 overestimated heart rate by an average of 6 bpm, while the Garmin Vivosmart HR underestimated by about 2 bpm.
For casual exercise tracking, a wrist device gives you a useful ballpark. If you need precision for training or a medical reason, a chest strap is significantly more reliable.
What Your Recovery Heart Rate Tells You
How quickly your heart rate drops after you stop exercising is one of the most telling signs of cardiovascular fitness. A healthy heart should drop by more than 12 bpm within the first minute of stopping. A landmark study published in the New England Journal of Medicine followed over 2,400 patients and found that people whose heart rate dropped by 12 bpm or less in that first minute had roughly double the risk of death over six years, even after accounting for age, sex, medications, and other cardiac risk factors.
This recovery rate reflects how well your nervous system shifts from “go” mode back to rest. Improving your aerobic fitness through regular exercise, particularly at moderate intensities, tends to improve this recovery speed over time. If you notice your heart rate stays elevated for several minutes after stopping moderate exercise, that’s worth mentioning at your next checkup.
Warning Signs to Stop
A heart rate that climbs above 85% of your max during intense exercise isn’t automatically dangerous for a healthy person, but certain symptoms during exercise signal a problem regardless of what number is on your watch. Chest pain or pressure, sudden dizziness or lightheadedness, feeling faint, unusual shortness of breath that’s out of proportion to your effort, and sudden weakness are all reasons to stop immediately. These symptoms can indicate an abnormal heart rhythm or inadequate blood flow to the heart, and they require prompt medical evaluation.
The number on your wrist matters less than how you feel. Heart rate zones are guidelines, not hard boundaries. If you feel good at 78% of your max, you’re fine. If you feel dizzy at 65%, something else is going on. Your body’s signals always take priority over a formula.