A good heart rate during exercise falls between 50% and 85% of your maximum heart rate, depending on your fitness goals and workout intensity. For a 40-year-old, that translates to roughly 90 to 153 beats per minute (bpm). The sweet spot within that range depends on whether you’re going for a long, steady run or pushing through high-intensity intervals.
Your maximum heart rate is the ceiling your heart can sustain during all-out effort. The simplest way to estimate it: subtract your age from 220. Once you know that number, every training zone is just a percentage of it.
Target Heart Rate by Age
The American Heart Association publishes target zones based on the 220-minus-age formula. Here’s what the 50% to 85% range looks like across ages:
- 20 years: 100–170 bpm (max: 200)
- 30 years: 95–162 bpm (max: 190)
- 35 years: 93–157 bpm (max: 185)
- 40 years: 90–153 bpm (max: 180)
- 45 years: 88–149 bpm (max: 175)
- 50 years: 85–145 bpm (max: 170)
- 55 years: 83–140 bpm (max: 165)
- 60 years: 80–136 bpm (max: 160)
- 65 years: 78–132 bpm (max: 155)
- 70 years: 75–128 bpm (max: 150)
These numbers are estimates. The 220-minus-age formula can be off by 10 to 12 bpm in either direction. A slightly more accurate alternative, sometimes called the Tanaka formula, is 208 minus 0.7 times your age. Research on marathon runners found that the standard formula tends to underestimate max heart rate in men by about 3 bpm and overestimate it in women by about 5 bpm. For most people doing regular workouts, either formula gets you close enough to train effectively.
The Five Heart Rate Zones Explained
That broad 50–85% range actually contains distinct training zones, each with different effects on your body. Knowing which zone you’re in helps you match your effort to your goal.
Zone 1 (50–60% of max) is your warm-up and cool-down pace. You can hold a full conversation without any strain. Your body burns almost entirely fat for fuel at this intensity. It’s also the right zone for recovery workouts between harder sessions.
Zone 2 (60–70% of max) is where most endurance training happens. You can still talk, but you might pause mid-sentence to catch your breath. Your body still relies heavily on fat for fuel. Long walks, easy jogs, and steady bike rides typically fall here. This is the zone to spend the most time in if you’re building a cardio base or training for a long-distance event.
Zone 3 (70–80% of max) feels comfortably hard. Conversation drops to short phrases. Your body starts pulling from a mix of fat, carbohydrates, and protein. This zone builds both strength and aerobic endurance, and it’s where many group fitness classes and tempo runs land.
Zone 4 (80–90% of max) is where talking takes real effort. You’re approaching your limit, and your body shifts to burning mainly carbohydrates and protein. Workouts in this zone build speed and power, but they’re taxing. Limiting zone 4 sessions to once or twice a week gives your body time to recover.
Zone 5 (90–100% of max) is an all-out sprint. You’re gasping, not talking. This forces your heart to work at peak capacity and builds fast-twitch muscle fibers used for explosive movements. Most people can only sustain zone 5 for 30 seconds to a few minutes.
Which Zone Is Best for Your Goal
If your primary goal is fat loss, zones 1 through 3 are your best bet. At lower intensities, your body preferentially burns stored fat for fuel. That doesn’t mean higher zones are useless for weight management (they still burn plenty of calories), but the fuel mix shifts toward carbohydrates and protein as intensity climbs.
For general cardiovascular fitness, spending most of your workout time in zones 2 and 3 is the most sustainable approach. These zones strengthen your heart and lungs without requiring long recovery periods. You can train in them four or five days a week without breaking down.
If you’re training for performance, whether that’s a faster 5K or more power on the bike, mixing in zone 4 and zone 5 intervals on top of a zone 2 base produces the best results. The classic approach is spending about 80% of your training time in zones 1 and 2, with the remaining 20% in zones 4 and 5.
A More Personalized Calculation
The standard percentage-of-max approach treats everyone with the same max heart rate equally, but someone with a resting heart rate of 55 bpm has a very different cardiovascular capacity than someone resting at 80 bpm. The heart rate reserve method (sometimes called the Karvonen method) accounts for this difference.
Here’s how it works: subtract your resting heart rate from your maximum heart rate. That gap is your heart rate reserve. To find a target, multiply your reserve by the desired intensity percentage, then add your resting heart rate back. For example, a 40-year-old with a resting heart rate of 60 bpm has a max of 180 and a reserve of 120. At 70% intensity, the target would be (120 × 0.70) + 60 = 144 bpm. This method gives a more accurate picture of how hard your heart is actually working relative to its capacity.
When Heart Rate Monitors Miss the Mark
Wrist-based optical heart rate monitors are convenient, but their accuracy varies with the type of exercise. During steady cycling, optical sensors match up with medical-grade chest monitors about 92% of the time, climbing as high as 98.5% once you’ve settled into a rhythm. During treadmill intervals, accuracy peaks around 89%. But during circuit-style weight training, accuracy drops to just 34.5%, meaning your watch may show a number that’s wildly off during strength workouts with lots of arm movement.
If you want reliable readings during varied workouts, a chest strap paired with your watch or phone will track more consistently. For steady cardio like running or cycling, most modern wrist sensors perform well enough to guide your training.
When Heart Rate Targets Don’t Apply
Beta-blockers and certain other blood pressure medications slow your heart rate as part of how they work. If you take one, you may never reach your calculated target heart rate no matter how hard you push. That doesn’t mean the workout isn’t effective.
In this situation, the “talk test” and perceived exertion scales are more useful guides. Most workouts should feel somewhat hard: you’re putting in effort, breathing is elevated, but you can keep going and say a few words at a time. If you can’t talk at all, you’re likely pushing too hard. If you can sing along to your playlist, you could probably push a bit more. This approach works for anyone, including people whose heart rate response is altered by medication, caffeine, dehydration, or stress.
Signs You’re Pushing Too Hard
Exceeding your max heart rate occasionally during a hard interval isn’t inherently dangerous for a healthy person, but certain symptoms during exercise signal that something more serious may be happening. Lightheadedness, a sudden fluttering or pounding sensation in your chest, breathlessness that seems out of proportion to your effort, or feeling like you might faint are all reasons to stop and rest immediately. These can indicate that your heart is beating too fast for the ventricles to fill properly, reducing blood flow to your brain.
A heart rate that spikes to 200 bpm or higher with no clear reason, or one that stays elevated well after you’ve stopped exercising, is worth paying attention to. These patterns can point to an electrical issue in the heart that’s unrelated to fitness level or effort.