A good active heart rate for most people falls between 50% and 85% of their maximum heart rate, depending on how intense the workout is. For a 40-year-old, that translates to roughly 90 to 153 beats per minute. The right number for you depends on your age, your fitness goals, and whether you’re aiming for a light endurance session or a hard interval workout.
How to Find Your Maximum Heart Rate
The simplest formula is 220 minus your age. If you’re 35, your estimated maximum heart rate is 185 bpm. A slightly more accurate version takes 207 minus 70% of your age, which gives a 35-year-old a max of about 183 bpm. Neither formula is perfect since individual variation is significant, but they give you a solid starting point for calculating your target zones.
Target Heart Rate by Age
The American Heart Association publishes a chart showing the 50% to 85% target zone for each age group. Here’s what that looks like in practice:
- Age 20: 100 to 170 bpm
- Age 30: 95 to 162 bpm
- Age 35: 93 to 157 bpm
- Age 40: 90 to 153 bpm
- Age 45: 88 to 149 bpm
- Age 50: 85 to 145 bpm
- Age 55: 83 to 140 bpm
- Age 60: 80 to 136 bpm
- Age 65: 78 to 132 bpm
- Age 70: 75 to 128 bpm
The lower end of each range (around 50% to 60% of max) is appropriate for beginners, warm-ups, and recovery days. The upper end (70% to 85%) corresponds to vigorous exercise like running, cycling at speed, or high-intensity interval training.
What Each Zone Does for Your Body
Not all heart rate zones produce the same results. At the lower end of your target range, roughly 50% to 70% of max, you’re in the aerobic zone. Your body primarily burns fat for fuel, and this is the sweet spot for building endurance over longer sessions. A brisk walk, easy jog, or steady bike ride typically keeps you here. It’s also the safest zone for people returning to exercise after time off or recovering from injury.
Push past about 80% to 85% of your max and you enter the anaerobic zone, where your body switches to burning carbohydrates and protein for quick energy. Training here strengthens your heart by forcing it to work near peak capacity and builds the fast-twitch muscle fibers that power sprints and explosive movements. You can’t sustain this intensity for long, which is why interval training alternates bursts in this zone with recovery periods at lower heart rates.
For general cardiovascular health, spending most of your exercise time in the moderate aerobic zone (roughly 50% to 70% of max) delivers the biggest long-term benefits. Mixing in one or two sessions per week at higher intensities adds fitness gains without the injury risk of going hard every day.
A More Personalized Calculation
The age-based chart works well as a rough guide, but it ignores one important variable: your resting heart rate. Someone with a resting heart rate of 55 bpm has a very different cardiovascular baseline than someone resting at 80 bpm, even if they’re the same age.
The heart rate reserve method accounts for this. First, find your resting heart rate by checking your pulse first thing in the morning before getting out of bed. Then subtract that number from your estimated maximum heart rate. The result is your heart rate reserve, which represents the actual working range your heart has available during exercise.
To find a personalized target, multiply your heart rate reserve by the intensity percentage you want (say, 60% for moderate exercise), then add your resting heart rate back in. For example, a 40-year-old with a resting heart rate of 65 bpm has a max of 180 and a reserve of 115. At 60% intensity, that’s 69 plus 65, giving a target of 134 bpm. Compare that to the simpler formula, which would put 60% of max at 108 bpm. The reserve method generally gives a more accurate picture of how hard your heart is actually working.
In cardiac rehabilitation settings, patients typically aim for 60% to 80% of heart rate reserve plus their resting heart rate. This approach is useful for anyone who wants a more tailored number, especially if your resting heart rate is unusually high or low.
When Heart Rate Numbers Don’t Apply
Several common situations can throw off your heart rate targets. Beta-blockers, prescribed for high blood pressure and certain heart conditions, slow your heart rate so significantly that you may never reach a standard target zone no matter how hard you push. If you take one of these medications, your doctor may recommend an exercise stress test to find a personalized target, or you can use perceived exertion instead. The Borg Rating of Perceived Exertion Scale lets you gauge intensity based on how hard you’re breathing and how tired you feel, bypassing heart rate numbers entirely.
Caffeine, dehydration, heat, stress, and poor sleep can all temporarily elevate your heart rate during exercise, making it look like you’re working harder than you actually are. If your heart rate seems unusually high on a given day, pay attention to how you feel rather than chasing a specific number.
Signs You’re Pushing Too Hard
Exercising above 85% of your maximum heart rate isn’t inherently dangerous for healthy people, but it should feel hard and it shouldn’t feel wrong. Warning signs that you’ve crossed from productive discomfort into overexertion include a racing or pounding heartbeat that feels irregular, chest pain, lightheadedness, and unusual shortness of breath that doesn’t match the effort you’re putting in. Fainting during exercise is a serious red flag that needs medical evaluation.
A practical rule: if you can’t say a short sentence out loud during moderate exercise, you’re likely above the moderate zone. If you can’t get any words out at all, you’re at or near your ceiling and should ease off unless you’re intentionally doing a short high-intensity interval.