Your heart rate during exercise should generally fall between 50% and 85% of your maximum heart rate, depending on how intense your workout is. For a 40-year-old, that translates to roughly 90 to 153 beats per minute. The exact range shifts with your age, fitness level, and workout goals.
Target Heart Rate by Age
The simplest way to estimate your maximum heart rate is to subtract your age from 220. From there, your target zone during exercise is a percentage of that number. The American Heart Association breaks it down like this:
- Age 20: 100 to 170 bpm
- Age 30: 95 to 162 bpm
- Age 40: 90 to 153 bpm
- Age 50: 85 to 145 bpm
- Age 60: 80 to 136 bpm
- Age 70: 75 to 128 bpm
Those ranges span from moderate to vigorous intensity. Moderate exercise sits at about 50% to 70% of your max, while vigorous exercise pushes you to 70% to 85%. A brisk walk might keep you in the lower half of your range; running, cycling hard, or doing HIIT will push you toward the upper end.
What Each Intensity Zone Does for You
Not every workout needs to be a sprint. Training at different heart rate levels produces different results, and most people benefit from spending the majority of their time at lower intensities rather than going all-out every session.
At 60% to 70% of your max heart rate, often called “Zone 2,” your body primarily burns fat for fuel. This zone strengthens your heart muscle so it can pump more blood with each beat, improves the energy-producing structures inside your cells, increases the number of small blood vessels around your muscles, and boosts red blood cell production to deliver more oxygen. It also trains your muscles to resist fatigue and keep going longer. Because the intensity is low, it places less strain on your tendons, ligaments, and joints, which makes it sustainable for longer sessions and reduces injury risk.
At 70% to 85% of your max, you’re in vigorous territory. This is where you build speed, power, and cardiovascular capacity. Interval training and tempo runs typically live here. These sessions are effective but taxing, so they work best as a smaller portion of your weekly training rather than the default.
A More Personalized Calculation
The 220-minus-age formula is a rough estimate. It can be off by 10 to 12 beats in either direction for a given individual. A few alternatives exist that researchers have found slightly more accurate:
- Tanaka formula: 208 minus (0.7 × your age)
- Gellish formula: 207 minus (0.7 × your age)
For a 45-year-old, the classic formula predicts a max of 175, while the Tanaka formula predicts 176.5. The difference is small at that age but grows more meaningful for older adults, where the 220 formula tends to underestimate true max heart rate.
If you want an even more tailored number, factor in your resting heart rate using the Karvonen method. First, find your resting heart rate by checking your pulse first thing in the morning for a few days and averaging the results. Then subtract that resting number from your estimated max. The result is your “heart rate reserve,” which represents the range your heart actually works within. Multiply that reserve by the percentage you’re targeting (say, 60% to 70% for moderate exercise), then add your resting heart rate back in. This approach accounts for your current fitness level, since a well-trained heart beats slower at rest, giving you a wider working range.
Why Your Heart Rate Might Not Match the Chart
Several factors can push your heart rate higher than expected during the same workout. Heat is one of the biggest. When you exercise in hot conditions, your body diverts blood toward your skin to cool you down, which forces your heart to beat faster to maintain the same output. Research in exercise physiology has documented heart rates roughly 10 beats per minute higher during the same effort in hot versus cool environments.
Dehydration compounds the problem. As you lose fluid through sweat, your blood volume drops, your heart has to work harder per beat, and your heart rate climbs progressively. The relationship is essentially linear: the more fluid you lose, the higher your heart rate drifts. On a hot day when you’re not drinking enough, a workout that normally keeps you at 130 bpm could easily push you past 145 for the same pace and effort.
Stress, poor sleep, and illness can also elevate your resting heart rate by several beats, which shifts your entire exercise range upward. If you track your heart rate regularly, a resting rate that’s notably higher than your baseline is a useful signal that your body is under extra strain.
Medications That Change the Rules
Beta-blockers, commonly prescribed for high blood pressure and certain heart conditions, suppress your heart rate response to exercise. If you take one, you may never reach your calculated target heart rate no matter how hard you push. Using standard heart rate zones to guide your intensity will be unreliable.
Instead, use perceived exertion as your guide. Most workouts should feel “somewhat hard,” meaning they take real effort but you can keep going and still hold a conversation. If you can’t talk while exercising, you’re likely working too hard. A structured perceived exertion scale (rated from 6 to 20) correlates well with heart rate during exercise testing, with research showing a strong relationship between the two measures in controlled settings. Your doctor can also use an exercise stress test to determine a personalized target that accounts for your medication.
How to Monitor During a Workout
A chest strap heart rate monitor is the most accurate option for real-time tracking. Wrist-based monitors on smartwatches have improved significantly but can lag during rapid heart rate changes and lose accuracy during activities with a lot of wrist movement, like rowing or boxing.
If you don’t have a monitor, the talk test is surprisingly reliable for moderate intensity. If you can speak in full sentences but couldn’t sing comfortably, you’re in the moderate zone. If you can only get out a few words before needing a breath, you’ve crossed into vigorous territory.
You can also check your pulse manually. Press two fingers against the side of your neck or the inside of your wrist, count the beats for 15 seconds, and multiply by four. Pause briefly during a rest interval rather than stopping mid-effort for the most practical reading.
What Your Heart Rate After Exercise Tells You
How quickly your heart rate drops after you stop exercising is a useful marker of cardiovascular fitness. A healthy recovery is a drop of 18 beats or more within the first minute after stopping vigorous activity. Fitter individuals often see drops of 20 to 30 beats or more. If your heart rate barely budges in that first minute, it may reflect lower fitness or, in some cases, a cardiovascular issue worth discussing with a provider.
Tracking heart rate recovery over weeks and months gives you a tangible way to see fitness improvements that the scale or mirror might not show. As your cardiovascular system gets stronger, that one-minute drop tends to get larger, even if your workout intensity stays the same.