Your cardio heart rate is the number of beats per minute your heart reaches during aerobic exercise, and the ideal range depends on your age and fitness level. For moderate-intensity cardio like brisk walking or easy cycling, you want to hit 50% to 70% of your maximum heart rate. For vigorous cardio like running or high-intensity classes, the target shifts to 70% to 85%.
How to Find Your Maximum Heart Rate
The simplest formula is one you’ve probably seen before: 220 minus your age. A 40-year-old gets a max of 180 beats per minute (bpm). It’s a rough estimate, though. A large meta-analysis found that a more accurate formula is 208 minus 0.7 times your age, which gives that same 40-year-old a max of 180 but becomes noticeably different at older ages. For a 65-year-old, the classic formula predicts 155 bpm while the updated one predicts 162. The old formula tends to underestimate max heart rate in older adults, which can lead to training zones that feel too easy.
Neither formula accounts for individual variation. Two 35-year-olds with identical fitness levels can have max heart rates that differ by 10 to 15 beats. If you use a heart rate monitor regularly and notice your actual peak is consistently higher or lower than the formula predicts, trust the monitor.
Heart Rate Zones Explained
Heart rate training zones divide the range between resting and maximum into bands, each with a different effect on your body:
- 50% to 60% of max: Light effort. Warm-ups, cool-downs, and active recovery days. You can hold a full conversation without any strain.
- 60% to 70% of max: Moderate effort. This is the classic “fat-burning zone” where your body draws the highest percentage of energy from stored fat. Comfortable enough to talk in complete sentences, though you’ll notice your breathing.
- 70% to 80% of max: The aerobic zone. This is where most cardio fitness gains happen. You can speak in short phrases but not give a speech. Sustained running, cycling, and swimming often land here.
- 80% to 90% of max: High intensity. Your body starts relying more on carbohydrates because it can’t deliver oxygen fast enough to burn fat efficiently. Talking becomes difficult. Interval training and tempo runs live in this range.
- 90% to 100% of max: Near-maximum effort. Sprints and all-out intervals. You can only sustain this for short bursts, typically 30 seconds to a few minutes.
For general cardiovascular health, spending most of your cardio time between 60% and 80% of your max heart rate gives you the broadest benefits. A common recommendation is to keep roughly 80% of your training in the moderate zones and save 20% for higher-intensity work.
The Fat-Burning Zone vs. Higher Intensity
The “fat-burning zone” is real but widely misunderstood. At around 60% to 70% of your max heart rate, your body does burn the highest proportion of calories from fat. Research pinpoints peak fat oxidation at roughly 54% of maximum oxygen uptake, which translates to somewhere between 60% and 80% of max heart rate for most people.
Here’s the catch: higher-intensity exercise burns more total calories per minute, including more total fat calories, even though a smaller percentage comes from fat. If your goal is weight loss, both zones work. Lower intensity is easier to sustain for longer sessions, while higher intensity gets more done in less time. The best zone is whichever one you’ll actually stick with consistently.
A More Personalized Calculation
The basic percentage-of-max method ignores one important variable: your resting heart rate. Someone with a resting rate of 55 bpm has a much wider working range than someone resting at 80 bpm, even if they’re the same age. The Karvonen formula accounts for this by using your heart rate reserve, which is the gap between your resting and maximum heart rates.
It works like this: Target heart rate equals your resting heart rate plus (heart rate reserve multiplied by the intensity percentage you want). So a 40-year-old with a resting rate of 60 and a max of 180 has a reserve of 120. To train at 70% intensity, the calculation is 60 + (120 × 0.70) = 144 bpm. Compare that to the simpler method, which would give 70% of 180 = 126 bpm. The Karvonen number is higher because it accounts for the fact that your heart is already doing work at rest.
To use this method, you need an accurate resting heart rate. Measure it first thing in the morning before getting out of bed, ideally averaged over several days.
What Your Resting Heart Rate Tells You
A normal resting heart rate falls between 60 and 100 bpm. Fit individuals typically rest in the 40 to 50 range, and elite endurance athletes can sit as low as 30 to 40 bpm. This happens because consistent cardio training makes the heart physically stronger. Each beat pumps a larger volume of blood (called stroke volume), so the heart doesn’t need to beat as often to circulate the same amount.
This adaptation is one of the clearest signs that cardio fitness is improving. If you’ve been training regularly for a few months and notice your resting heart rate dropping by a few beats, your heart is literally becoming more efficient. The same principle explains why your heart rate during a familiar workout gradually decreases over time: your cardiovascular system can handle the same workload with less effort.
How Accurate Is Your Monitor
Chest straps remain the gold standard for heart rate accuracy during exercise. Studies show chest-strap monitors have a mean error of less than 1%, with over 99% of detected beats being real heartbeats. Wrist-based optical sensors, like those in most smartwatches, are reasonably good during steady-state cardio but less reliable during high-intensity or fast-changing efforts. Error rates for wrist sensors typically run around 3% to 5%, and they can spike higher during intervals or exercises with a lot of wrist movement.
For zone-based training where a few beats per minute matter, a chest strap is worth the investment. For general tracking to confirm you’re in a moderate or vigorous range, a wrist sensor is usually close enough.
When Medications Change the Numbers
Beta-blockers, prescribed for high blood pressure, heart failure, and other cardiovascular conditions, directly lower heart rate at rest and during exercise. Research shows they reduce resting heart rate by about 18% and maximum heart rate by roughly 19%. Someone whose unmedicated max would be 170 bpm might only reach 138 on a beta-blocker.
This means the standard age-based formulas won’t work if you take these medications. Your zones will be significantly lower across the board. If you’re on beta-blockers or other heart rate-altering medications, the perceived exertion method (rating how hard the effort feels on a scale of 1 to 10) is often more useful than chasing a specific number. A “moderate” effort should feel like a 4 to 6 out of 10, regardless of what your heart rate reads.
Putting It Into Practice
Start by estimating your max heart rate using 208 minus 0.7 times your age. If you know your resting heart rate, use the Karvonen formula for more personalized zones. For most cardio sessions aimed at general fitness, keep your heart rate between 60% and 80% of your max. That’s the range where you build endurance, strengthen your heart, and burn a solid mix of fat and carbohydrates.
If you’re new to exercise, stay in the 50% to 65% range until sustained effort feels comfortable, then gradually push into higher zones. If you’ve been training for a while and want to improve performance, adding one or two sessions per week in the 80% to 90% range can push your fitness forward faster than staying in the moderate zone alone. Pay attention to how your body responds over weeks and months. A dropping resting heart rate and the ability to do more work at the same heart rate are the clearest signs your cardiovascular system is adapting.