During exercise, your heart rate should generally fall between 50% and 85% of your maximum heart rate, depending on how hard you’re working. For a 40-year-old, that means roughly 90 to 153 beats per minute. The exact range depends on your age, fitness level, and workout goals.
How to Estimate Your Maximum Heart Rate
Your maximum heart rate is the ceiling your heart can reach during all-out effort. The simplest way to estimate it is with the formula the American Heart Association uses: 220 minus your age. A 30-year-old gets a max of 190 bpm, a 50-year-old gets 170 bpm, and so on.
A slightly more refined formula, developed by researcher Hirofumi Tanaka, calculates it as 208 minus 0.7 times your age. For a 40-year-old, that gives 180 bpm instead of 180 from the simpler formula (they happen to converge at that age), but the two formulas diverge more at younger and older ages. Tanaka’s version tends to be more accurate for older adults because it was validated across a wider range of ages. Either formula gives you a reasonable starting point, not a precise number. Individual max heart rates can vary by 10 to 20 beats in either direction from these estimates.
Target Zones for Moderate and Vigorous Exercise
Once you have your estimated max, the American Heart Association breaks exercise intensity into two main zones. Moderate intensity sits at 50% to 70% of your max. This is the zone for brisk walking, casual cycling, or an easy swim. You can hold a conversation but you’re clearly working harder than at rest. Vigorous intensity runs from 70% to 85% of your max, covering activities like running, fast cycling, competitive sports, or high-intensity interval training.
Here’s what those zones look like across age groups:
- Age 20: 100 to 170 bpm (max ~200)
- Age 30: 95 to 162 bpm (max ~190)
- Age 40: 90 to 153 bpm (max ~180)
- Age 50: 85 to 145 bpm (max ~170)
- Age 60: 80 to 136 bpm (max ~160)
- Age 70: 75 to 128 bpm (max ~150)
If you’re just starting to exercise or returning after a long break, aim for the lower end of the moderate zone (50% to 60%) and build up over weeks. If you’re training for performance, you’ll spend more time in the vigorous range, with occasional bursts above 85% during interval workouts.
The Talk Test as a Backup
Heart rate numbers are useful, but they’re not the only way to gauge intensity. The talk test is surprisingly reliable: during moderate exercise, you can talk in full sentences but not sing. During vigorous exercise, you can only get out a few words before needing a breath. This matters especially if you take medications that affect your heart rate (more on that below) or if your personal max heart rate differs significantly from the age-based estimate.
A more structured version of this approach is the rating of perceived exertion scale, where you rate how hard the effort feels on a scale of 6 to 20. Moderate exercise typically feels like a 12 to 14, and vigorous falls around 15 to 17. It’s subjective, but it tracks well with actual heart rate data for most people.
Why Your Numbers Might Not Match the Chart
Several things can push your exercise heart rate higher or lower than expected, even at the same effort level.
Heat and dehydration are the biggest environmental factors. When you exercise in hot conditions, your body diverts blood to the skin for cooling, which reduces the volume of blood your heart pumps per beat. Your heart compensates by beating faster. Research in exercise physiology shows that staying well hydrated in the heat can fully prevent this extra rise in heart rate, while exercising in cool conditions also keeps it in check. On a hot day, seeing your heart rate 10 to 15 beats higher than usual at the same pace is normal and not necessarily a sign you’re working harder at a muscular level.
Beta-blockers, commonly prescribed for high blood pressure, anxiety, and heart conditions, lower both resting and exercise heart rate significantly. Studies show they reduce maximum heart rate by about 19%, meaning someone whose predicted max is 180 might only reach around 146 on the medication. If you take a beta-blocker, the standard heart rate zones don’t apply to you. The talk test and perceived exertion become your primary tools for gauging workout intensity.
Caffeine, sleep deprivation, and stress can all elevate resting heart rate, which sometimes carries over into exercise. A poor night’s sleep might add 5 to 10 beats to your usual numbers. This doesn’t mean you’re getting a better workout. It means your body is under additional strain.
How Accurate Is Your Wrist Monitor?
If you’re tracking heart rate with a smartwatch or fitness band, accuracy varies quite a bit by device and exercise intensity. A study comparing commercial monitors against medical-grade ECG found that chest straps (like the Polar H7) had the highest agreement at 98% concordance with ECG readings. The Apple Watch came in next at 96%. Other wrist-worn devices like the Fitbit and Garmin models scored around 89%.
The bigger issue is that wrist-based optical sensors become less reliable at higher intensities. At running speeds of 8 to 9 mph, none of the wrist-worn devices in the study maintained strong accuracy. Some overestimated heart rate by an average of 6 bpm, while others underestimated by about 2 bpm. For casual monitoring during moderate exercise, a wrist device works fine. If you need precise data during intense training, a chest strap is significantly more reliable.
Signs You’ve Pushed Too High
Exceeding 85% of your max heart rate for short bursts during interval training is generally safe for healthy people. But certain warning signs during exercise suggest your heart is under more stress than it can handle. Dizziness, lightheadedness, chest pain or pressure, and feeling like you might faint are all signals to stop immediately and rest. Severe shortness of breath that feels disproportionate to the effort is another red flag.
These symptoms can occur at any heart rate, not just at very high numbers. Someone with an undiagnosed heart condition might experience them at 140 bpm, while a trained athlete might feel fine at 185. The symptoms matter more than the number on your watch.
What Heart Rate Recovery Tells You
How quickly your heart rate drops after you stop exercising is actually a better indicator of cardiovascular fitness than how high it goes during a workout. A healthy recovery means your heart rate drops by at least 18 beats within the first minute after stopping vigorous exercise. A faster drop generally reflects better fitness and a healthier nervous system response.
You can track this easily: note your heart rate when you finish your hardest effort, then check it again after 60 seconds of standing or slow walking. Over weeks of consistent training, you should see this recovery number improve, which is one of the most meaningful signs that your cardiovascular fitness is getting better, even if your weight or pace hasn’t changed much yet.