Your heart rate during exercise should fall 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, aim for 70% to 85%. The trick is knowing your personal maximum, which changes with age.
How to Find Your Maximum Heart Rate
The simplest formula is 220 minus your age. If you’re 40, your estimated maximum heart rate is 180 beats per minute. This is the Fox formula, and it’s been used in gyms and doctor’s offices for decades. A slightly more accurate version, developed by researcher Hirofumi Tanaka, uses 208 minus 0.7 times your age. For that same 40-year-old, Tanaka’s equation gives a max of 180 as well, but the two formulas diverge more at younger and older ages.
Both formulas are estimates. Your true maximum heart rate can be 10 to 20 beats higher or lower than what the math predicts. Still, these equations give you a useful starting point for building your target zones.
Target Zones by Exercise Intensity
The American Heart Association breaks exercise into two main intensity levels, each tied to a percentage of your maximum heart rate:
- Moderate intensity (50% to 70%): Brisk walking, casual cycling, water aerobics. You can hold a conversation but not sing. For a 40-year-old with a max of 180, this means roughly 90 to 126 beats per minute.
- Vigorous intensity (70% to 85%): Running, fast cycling, competitive sports. You can speak a few words at a time but not carry on a full conversation. For that same 40-year-old, the range is about 126 to 153 beats per minute.
Here’s how the numbers shift across ages, using the 220-minus-age formula:
- Age 25: Max ~195. Moderate zone: 98–137. Vigorous zone: 137–166.
- Age 35: Max ~185. Moderate zone: 93–130. Vigorous zone: 130–157.
- Age 45: Max ~175. Moderate zone: 88–123. Vigorous zone: 123–149.
- Age 55: Max ~165. Moderate zone: 83–116. Vigorous zone: 116–140.
- Age 65: Max ~155. Moderate zone: 78–109. Vigorous zone: 109–132.
A More Personalized Calculation
The basic percentage method treats everyone with the same max heart rate identically, regardless of fitness level. The Karvonen method (also called heart rate reserve) adds your resting heart rate into the equation, which makes the result more personal. Someone with a resting heart rate of 55 is in a different cardiovascular place than someone resting at 80, even if they’re the same age.
To use it, first find your heart rate reserve: subtract your resting heart rate from your maximum heart rate. Then multiply that number by your desired intensity percentage, and add your resting heart rate back. So for a 40-year-old with a resting heart rate of 65 and a max of 180, the heart rate reserve is 115. At 60% intensity, the target would be (115 × 0.60) + 65, which equals 134 beats per minute. The standard percentage method would give 108 at 60%, a meaningfully lower number.
Cardiac rehab programs commonly use heart rate reserve to set exercise targets between 60% and 80%, because it better reflects what an individual heart is actually doing during effort.
When Heart Rate Zones Don’t Apply
If you take a beta-blocker or certain other blood pressure medications, standard heart rate targets won’t work for you. Beta-blockers lower both your resting heart rate and your heart’s ability to speed up during exercise. One approach is to reduce your target by about 10 beats per minute (roughly the amount a beta-blocker lowers resting heart rate), but even that adjustment is imperfect because the medication blunts the normal rise in heart rate throughout a workout, not just at rest.
The better option in this case is perceived exertion. The Borg Rating of Perceived Exertion scale runs from 6 (no effort at all) to 20 (absolute maximum). A rating of 12 to 14, described as “somewhat hard,” corresponds roughly to moderate-intensity exercise. You’re breathing harder, your heart feels like it’s working, but you’re not gasping. This scale is useful for anyone, but it’s especially valuable when medications or medical conditions make heart rate an unreliable guide.
How Accurate Is Your Wrist Monitor?
Optical heart rate sensors on smartwatches work by shining light into your skin and measuring blood flow changes. During steady-state cardio like cycling, accuracy can be excellent, with readings falling within 5 beats per minute of a medical-grade ECG about 92% of the time. During treadmill running, accuracy reaches around 89% at best. But during activities with lots of wrist movement, like circuit training with weights, accuracy drops dramatically, to as low as 35%.
Chest strap monitors remain more reliable across all exercise types because they detect the electrical signals of your heartbeat directly, similar to how an ECG works. If you’re using heart rate zones to guide serious training, a chest strap is worth the investment. For general fitness, a wrist sensor is fine for steady activities like walking, jogging, or cycling, just know it may lag or misread during exercises that involve gripping, twisting, or rapid arm movements.
What Your Recovery Heart Rate Tells You
How quickly your heart rate drops after you stop exercising is one of the simplest markers of cardiovascular fitness. A healthy recovery is a drop of at least 18 beats per minute within the first minute of rest. If you’re at 160 during a hard run and you’re down to 140 or lower after standing still for 60 seconds, your heart is recovering well.
A slower recovery doesn’t necessarily mean something is wrong, especially if you’re just starting an exercise program. But it’s a number worth tracking over time. As your fitness improves, you should see that one-minute drop get larger, which reflects your heart’s growing ability to shift quickly between effort and rest. If your recovery rate stays flat or worsens over weeks despite consistent training, it’s a signal worth mentioning to your doctor.
Sex and Fitness Level Differences
Research shows that men tend to have slightly higher maximum heart rates than women, roughly 198 versus 190 beats per minute in one study of young, healthy adults. This gap holds regardless of activity level. Sedentary individuals also tend to have higher observed max heart rates than active people, likely because trained hearts pump more blood per beat and don’t need to beat as fast to reach peak output.
Despite these differences, the Tanaka formula (208 minus 0.7 times age) performs reasonably well across both sexes and fitness levels. If you want precision, a graded exercise test supervised by a professional will give you your actual max heart rate. But for everyday exercise planning, the standard formulas with the target zone percentages will keep most people in the right range.