Your heart rate needs to reach about 50% of your maximum to count as cardio, with the most common training range falling between 50% and 85% of your max. For a 30-year-old with a maximum heart rate around 190 beats per minute (bpm), that means cardio starts at roughly 95 bpm and tops out around 162 bpm. The exact numbers shift with your age, fitness level, and resting heart rate.
The Two Main Cardio Zones
The American Heart Association breaks cardio into two intensity levels, both defined as a percentage of your maximum heart rate. Moderate-intensity cardio falls between 50% and 70% of your max. This is the zone you’d hit during a brisk walk, a casual bike ride, or an easy swim. You can hold a conversation, but you’re breathing harder than normal.
Vigorous-intensity cardio sits between 70% and 85% of your max. Running, fast cycling, jump rope, and high-intensity group classes live here. You can speak in short phrases but not carry on a full conversation. Both zones deliver cardiovascular benefits, so you don’t need to push into vigorous territory to get a meaningful workout.
How to Find Your Maximum Heart Rate
The classic formula is simple: 220 minus your age. A 40-year-old gets an estimated max of 180 bpm, a 50-year-old gets 170, and so on. This formula, known as the Fox formula, has been used since 1971 and remains the most widely cited starting point.
A newer formula, 208 minus 0.7 times your age, tends to be slightly more accurate. Research on marathon runners found that the older Fox formula underestimates max heart rate in men by about 3 bpm, while the newer version tracks closer to measured values in men. Both formulas overestimate max heart rate in women by roughly 5 bpm. Neither is perfect, but they give you a reasonable ballpark.
Here’s what the cardio zones look like at different ages using the 220-minus-age formula:
- Age 25 (max ~195 bpm): Moderate zone 98–137, vigorous zone 137–166
- Age 35 (max ~185 bpm): Moderate zone 93–130, vigorous zone 130–157
- Age 45 (max ~175 bpm): Moderate zone 88–123, vigorous zone 123–149
- Age 55 (max ~165 bpm): Moderate zone 83–116, vigorous zone 116–140
- Age 65 (max ~155 bpm): 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, but two people with the same max can have very different fitness levels. Someone with a resting heart rate of 55 bpm has a lot more capacity to work with than someone resting at 80 bpm.
The Karvonen method accounts for this by using your heart rate reserve, which is your maximum heart rate minus your resting heart rate. To find a target, you multiply that reserve by the percentage you want, then add your resting heart rate back in. For example, a 40-year-old with a resting heart rate of 60 bpm has a heart rate reserve of 120 (180 minus 60). To hit 60% intensity: 120 times 0.60, plus 60, equals 132 bpm. This approach produces a more tailored target, especially for people who are very fit or just starting out. Cleveland Clinic notes that cardiac rehab programs typically aim for 60% to 80% of heart rate reserve.
To measure your resting heart rate accurately, check your pulse first thing in the morning before getting out of bed. Count beats for 30 seconds and double it, or use a fitness tracker that logs overnight heart rate.
What Happens Above 85%
Once your heart rate climbs above roughly 80% of your max, your body starts shifting from aerobic metabolism (using oxygen to burn fuel) to anaerobic metabolism (burning fuel faster than oxygen can keep up). This is the threshold where lactic acid builds up, your muscles start to burn, and you can only sustain the effort for short bursts.
Training at 80% to 90% of your max still has cardiovascular benefits and improves speed and power, but it isn’t sustainable for long sessions. Most people doing general fitness cardio don’t need to spend much time here. If you’re training for performance, interval workouts that spike into this range and then recover are the typical approach.
When Heart Rate Isn’t Reliable
Certain medications change the equation entirely. Beta-blockers, commonly prescribed for high blood pressure and heart conditions, slow the heart rate so significantly that you may never reach your calculated target no matter how hard you push. If you take a beta-blocker and try to use standard heart rate zones, you’ll think you’re barely working when you’re actually at a solid effort level.
In these situations, perceived exertion is a better guide. The Borg Rating of Perceived Exertion scale asks you to rate how hard you feel you’re working on a scale from 6 to 20. Research shows a strong correlation between RPE and actual heart rate during exercise, with the general rule that multiplying your RPE by 10 gives a rough estimate of your heart rate. For moderate cardio, you’d aim for an RPE of about 12 to 14 (“somewhat hard”). For vigorous effort, 15 to 17 (“hard” to “very hard”).
Other factors that can throw off heart rate readings include caffeine, dehydration, heat, stress, and sleep deprivation. All of these can elevate your heart rate independently of how hard you’re exercising. If your heart rate seems unusually high for a given effort level, those variables are worth considering before you assume you’re overtraining.
Picking the Right Zone for Your Goal
If your primary goal is general heart health and longevity, moderate-intensity cardio (50% to 70% of max) done consistently is the most effective and sustainable approach. The American Heart Association recommends at least 150 minutes per week at this level, or 75 minutes of vigorous activity.
If you want to improve endurance or athletic performance, spending most of your training time in the moderate zone with occasional sessions in the vigorous zone (70% to 85%) follows the pattern used by most successful endurance athletes. The common split is roughly 80% of training at moderate intensity and 20% at higher intensity.
If weight loss is the goal, the specific zone matters less than total calories burned. Vigorous exercise burns more calories per minute, but moderate exercise is easier to sustain for longer sessions. The best cardio zone for fat loss is whichever one you’ll actually do consistently.