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%. For vigorous exercise like running or cycling hard, aim for 70% to 85%. The simplest way to estimate your maximum heart rate is to subtract your age from 220, which gives you the ceiling from which all your training zones are calculated.
How to Find Your Maximum Heart Rate
The classic formula, 220 minus your age, has been the standard since 1971. If you’re 40 years old, your estimated max is 180 bpm. If you’re 55, it’s 165 bpm. It’s a rough tool, though, and can be off by 10 to 12 beats per minute in either direction. A slightly more accurate formula, developed by Tanaka and colleagues, is 208 minus 0.7 times your age. For a 40-year-old, that gives 180 bpm (the same in this case), but the two formulas diverge more at younger and older ages.
Neither formula is perfect. Research on marathon runners found that the classic formula overestimates maximum heart rate in women by about 5 bpm and underestimates it in men by about 3 bpm. These are population averages, so your individual max could vary even more. If you’ve ever hit a heart rate during a hard sprint that exceeds your calculated max, your true maximum is simply higher than the formula predicted. That’s normal.
Target Heart Rate by Age
The American Heart Association provides a straightforward chart based on the 220-minus-age formula. Your target zone spans from 50% (light effort) to 85% (near-max effort) of that number:
- Age 20: 100 to 170 bpm (max: 200)
- Age 30: 95 to 162 bpm (max: 190)
- Age 35: 93 to 157 bpm (max: 185)
- Age 40: 90 to 153 bpm (max: 180)
- Age 45: 88 to 149 bpm (max: 175)
- Age 50: 85 to 145 bpm (max: 170)
- Age 55: 83 to 140 bpm (max: 165)
- Age 60: 80 to 136 bpm (max: 160)
- Age 65: 78 to 132 bpm (max: 155)
- Age 70: 75 to 128 bpm (max: 150)
If you’re just starting a fitness routine, stay near the lower end of your range and build up gradually. Over weeks, you’ll find the same pace feels easier at the same heart rate, which is a sign your cardiovascular fitness is improving.
The Five Heart Rate Zones
Most fitness trackers and training plans break exercise intensity into five zones, each defined as a percentage of your maximum heart rate. These zones aren’t rigid boundaries. They’re ranges that help you match your effort to your goal.
Zone 1 (50% to 60%): Easy enough to hold a full conversation. This is your warm-up, cool-down, and recovery pace. It builds a base without stressing your body.
Zone 2 (60% to 70%): You can still talk, but you’ll pause for breath between sentences. This is the sweet spot for longer sessions that build endurance. It’s also where your body burns the highest percentage of calories from fat, roughly 65% of total calories burned at this intensity.
Zone 3 (70% to 80%): Conversation drops to short phrases. This feels comfortably hard and builds both strength and aerobic capacity. You burn more total calories here than in Zone 2, though a smaller share (about 45%) comes from fat.
Zone 4 (80% to 90%): Talking takes real effort. You’re pushing toward your limit, building speed and power. Intervals and tempo runs typically land here.
Zone 5 (90% to 100%): All-out effort. You can sustain this for only short bursts, typically under a few minutes. It strengthens your heart by forcing it to work at peak capacity and recruits fast-twitch muscle fibers used for sprinting and explosive movement.
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 is starting from a very different baseline than someone at 80 bpm, even if they’re the same age. The Karvonen method accounts for this by using something called heart rate reserve, which is your maximum heart rate minus your resting heart rate.
Here’s how it works. First, find your resting heart rate by checking your pulse first thing in the morning before getting out of bed. Count beats for 60 seconds, or use a fitness tracker’s overnight reading. Then subtract that number from your estimated max. The result is your heart rate reserve. To find a target zone, multiply the reserve by the percentage you want, then add your resting heart rate back.
For example, a 40-year-old with a resting heart rate of 65 bpm has a max of 180 and a reserve of 115. To exercise at 70% intensity: 115 × 0.70 = 80.5, plus 65 = about 146 bpm. Using the simpler method (70% of 180), the target would be 126 bpm. That’s a 20-beat difference, which is significant. The Karvonen method is generally considered more accurate because it reflects your individual fitness level, not just your age.
Why the “Fat Burning Zone” Is Misleading
You’ve probably seen treadmills display a “fat burning zone” around 60% to 70% of max. It’s technically true that a higher percentage of calories burned at this intensity come from fat. But the total number of calories burned is lower than at higher intensities. A 30-minute jog in Zone 3 burns more total fat and more total calories than a 30-minute walk in Zone 2, even though the percentage from fat is smaller. If your goal is weight management, overall calorie burn matters more than the fuel source your body prefers at a given pace.
When Your Watch Might Be Wrong
Wrist-based optical heart rate sensors are convenient but less reliable during intense or fast-changing efforts. Compared to chest straps, wrist and armband sensors can drift by roughly 9 to 10 bpm in either direction during hard intervals. One study found armband monitors overestimated heart rate by about 5 bpm at high intensity. Chest straps that use electrical signals (similar to an ECG) agree with each other to within about 3 bpm and are more trustworthy for zone-based training.
For casual exercisers, a wrist sensor is fine for general guidance. If you’re doing structured interval training and using specific heart rate targets, a chest strap will give you more reliable data.
Beta Blockers Change the Rules
If you take beta blockers for blood pressure or a heart condition, the standard formulas won’t work for you. These medications slow your heart rate at rest and during exercise, which means your actual maximum will be significantly lower than 220 minus your age would predict. Instead of relying on heart rate numbers, use the talk test: during moderate exercise you should be able to speak in short sentences with pauses for breath. If you’re breathing so hard you can’t talk at all, you’re at high intensity.
Warning Signs to Take Seriously
A high heart rate during hard exercise is expected and normal. What isn’t normal is a heart rate that spikes or feels irregular along with symptoms like chest pain, dizziness, lightheadedness, fainting, or sudden shortness of breath that seems out of proportion to your effort. These can signal an abnormal heart rhythm. Ventricular tachycardia, a dangerously fast rhythm originating in the lower chambers of the heart, can become life-threatening if it lasts more than a few seconds. If you experience any combination of these symptoms during exercise, stop immediately and get help.