A good heart rate during exercise falls between 50% and 85% of your maximum heart rate, depending on how intense you want your workout to be. For moderate exercise like brisk walking or easy cycling, aim for 50% to 70% of your max. For vigorous exercise like running or high-intensity intervals, aim for 70% to 85%. The key number you need first is your estimated maximum heart rate, which you can calculate with a simple formula based on your age.
How to Find Your Maximum Heart Rate
The most widely used formula is 220 minus your age. If you’re 40, your estimated max is 180 beats per minute (bpm). It’s simple, but it can be off by 10 to 12 beats per minute in either direction. A slightly more accurate version, developed by researcher Hirofumi Tanaka, is 208 minus 0.7 times your age. For a 40-year-old, that gives 180 as well, but the two formulas diverge more at younger and older ages.
Neither formula is perfect. Individual genetics, fitness level, and even medications can shift your true maximum significantly. If precision matters to you, an exercise stress test supervised by a healthcare provider will give you an actual measured number rather than an estimate.
Target Heart Rate by Age
The American Heart Association publishes a straightforward chart using the 50% to 85% range. Here’s what it looks like across age groups:
- Age 20: 100 to 170 bpm (max: 200)
- Age 30: 95 to 162 bpm (max: 190)
- Age 35: 93 to 157 bpm (max: 185)
- Age 40: 90 to 153 bpm (max: 180)
- Age 45: 88 to 149 bpm (max: 175)
- Age 50: 85 to 145 bpm (max: 170)
- Age 55: 83 to 140 bpm (max: 165)
- Age 60: 80 to 136 bpm (max: 160)
- Age 65: 78 to 132 bpm (max: 155)
- Age 70: 75 to 128 bpm (max: 150)
The lower end of each range suits moderate activities like a brisk walk. The upper end corresponds to hard efforts like running hills or intense cycling.
The Five Heart Rate Zones
If you use a fitness tracker or smartwatch, you’ve probably seen references to heart rate “zones.” These break the full range into five tiers, each with a different training effect.
- Zone 1 (50% to 60% of max): Very light effort. Walking, warming up, or active recovery. Your body burns primarily fat at this intensity, but total calorie burn is low.
- Zone 2 (60% to 70%): Moderate effort. You can hold a full conversation. This is the zone endurance athletes spend most of their training in. It builds aerobic fitness and still relies heavily on fat for fuel.
- Zone 3 (70% to 80%): Moderate to hard. Talking becomes choppy. Your body shifts to a mix of fat, carbohydrates, and protein for energy. Tempo runs and steady-state cycling typically fall here.
- Zone 4 (80% to 90%): Hard effort. You can only manage a few words at a time. This zone improves your lactate threshold, the point at which your muscles start fatiguing quickly. Fuel comes mainly from carbohydrates.
- Zone 5 (90% to 100%): All-out effort. Sprints, intervals, finishing kicks. You can sustain this for only a minute or two. It builds top-end speed and power but demands significant recovery.
For general fitness, most of your workout time is best spent in Zones 2 and 3, with occasional pushes into Zone 4. Zone 5 is reserved for trained athletes or short interval bursts.
A More Personalized Calculation
The simple percentage-of-max approach treats everyone the same regardless of fitness. A more personalized method uses your heart rate reserve, which accounts for your resting heart rate. Someone with a resting heart rate of 55 bpm is in a very different starting position than someone resting at 80 bpm, even if they’re the same age.
Here’s how it works. First, subtract your resting heart rate from your maximum heart rate. That difference is your heart rate reserve. Then multiply the reserve by the percentage intensity you want (say, 60% for moderate exercise) and add your resting heart rate back. For a 40-year-old with a max of 180 and a resting rate of 60:
Heart rate reserve = 180 minus 60 = 120. Target at 60% intensity = (120 × 0.60) + 60 = 132 bpm. At 80% intensity = (120 × 0.80) + 60 = 156 bpm.
This method, sometimes called the Karvonen formula, produces targets that better reflect your actual cardiovascular fitness. To use it, measure your resting heart rate first thing in the morning before getting out of bed, over several days, and average the results.
What Counts as Fat Burning
The “fat-burning zone” is one of the most misunderstood concepts in fitness. Your body does burn the highest proportion of fat at lower intensities, roughly 57% to 76% of your maximum heart rate according to guidelines from the American College of Sports Medicine. That corresponds roughly to Zones 2 and 3.
But proportion isn’t the whole story. Higher-intensity exercise burns more total calories per minute, so even though a smaller percentage comes from fat, the absolute amount of fat burned can be similar or higher. The best exercise intensity for losing body fat is whichever one you can sustain consistently. If Zone 2 keeps you exercising for 45 minutes while Zone 4 wipes you out in 15, the lower intensity wins.
Why Your Heart Rate Might Run Higher Than Expected
If your heart rate seems unusually high for the effort you’re putting in, environmental conditions are a common culprit. Heat and humidity force your heart to work harder to cool your body, pushing your rate up even at the same pace or resistance. Research from the Journal of Applied Physiology shows that cardiovascular strain increases before you even feel overheated, meaning your heart rate rises as an early signal well before you notice you’re struggling with the heat. Altitude has a similar effect because your body compensates for lower oxygen levels by pumping faster.
Dehydration, poor sleep, caffeine, and stress can all elevate your exercise heart rate too. If you notice your numbers drifting upward on a given day, it doesn’t necessarily mean you’re less fit. It often just means your body is dealing with an extra stressor.
When Medications Change the Rules
Beta blockers, commonly prescribed for high blood pressure and certain heart conditions, slow the heart rate. If you take one, you may never reach your calculated target heart rate no matter how hard you push. This doesn’t mean the workout isn’t effective. It means the standard formulas don’t apply to you.
In this situation, a perceived exertion scale is more useful than a number on your wrist. The Borg Rating of Perceived Exertion Scale asks you to judge your effort on a scale based on how hard you’re breathing, how tired your muscles feel, and how much energy the activity demands. A stress test can also help your provider determine a personalized target that accounts for the medication’s effect on your heart.
Warning Signs to Take Seriously
Pushing into higher heart rate zones is normal during intense exercise, but certain symptoms signal something beyond ordinary exertion. Chest tightness, squeezing, heaviness, or burning, especially if it spreads to your arm, jaw, shoulder, or back, is a red flag. So is sudden shortness of breath during activity that normally feels manageable, an irregular or skipping heartbeat, dizziness, or feeling faint.
Unusual fatigue during mild or moderate activity, where you feel drained doing something that used to be easy, can also indicate a cardiac issue. Cold, clammy skin or sudden sweating paired with chest discomfort or nausea is particularly concerning. If any of these occur, stop exercising immediately. Chest pain that doesn’t resolve, severe breathing difficulty, fainting, or radiating pain warrant emergency medical attention.