Your target heart rate is a percentage of your maximum heart rate, and the simplest way to find it starts with one formula: 220 minus your age. That gives you an estimated maximum. From there, you multiply by the intensity percentage you want to hit during exercise. For moderate activity, aim for 50% to 70% of your max. For vigorous exercise, aim for 70% to 85%.
That’s the quick version. But the more precisely you calculate it, the more useful it becomes, especially once you factor in your resting heart rate and fitness level.
The Basic Formula
The most widely used method is the Fox formula: subtract your age from 220. A 40-year-old gets an estimated max heart rate of 180 beats per minute. A 55-year-old gets 165. It’s a rough estimate, not a measurement, and your actual max could be somewhat higher or lower depending on your genetics and fitness level. But it’s the starting point most guidelines use.
Once you have your max, multiply it by the percentage range for the intensity you’re targeting:
- Moderate intensity: 50% to 70% of max
- Vigorous intensity: 70% to 85% of max
So for that 40-year-old with a max of 180: moderate exercise means keeping your heart rate between 90 and 126 bpm, and vigorous exercise means 126 to 153 bpm.
Target Heart Rate by Age
The American Heart Association publishes a reference chart covering the full 50% to 85% training zone. Here’s what it looks like across age groups:
- 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 your age falls between these numbers, just run the formula yourself. The math takes about 10 seconds.
A More Accurate Method: Heart Rate Reserve
The basic formula treats everyone the same age as identical, which they obviously aren’t. A 45-year-old who runs regularly has a very different cardiovascular baseline than a 45-year-old who’s been sedentary for years. The Karvonen method (also called the heart rate reserve method) accounts for this by folding in your resting heart rate.
Here’s how it works, step by step:
Step 1: Find your max heart rate. Use 220 minus your age, or for a slightly refined estimate, use 208 minus (0.7 times your age). The second formula tends to be a bit more accurate for older adults.
Step 2: Measure your resting heart rate. This is the number of times your heart beats per minute when you’re completely at rest. The best way to get it is described in the next section.
Step 3: Subtract your resting heart rate from your max. This number is your heart rate reserve.
Step 4: Multiply your heart rate reserve by the percentage of intensity you want (say, 0.60 for 60% or 0.80 for 80%), then add your resting heart rate back in.
Here’s a concrete example. A 40-year-old with a resting heart rate of 65 bpm:
- Max heart rate: 220 minus 40 = 180
- Heart rate reserve: 180 minus 65 = 115
- 60% intensity target: (115 × 0.60) + 65 = 134 bpm
- 80% intensity target: (115 × 0.80) + 65 = 157 bpm
Compare that to the basic formula, which would put 60% intensity at 108 bpm and 80% at 144 bpm. The Karvonen method produces higher targets because it accounts for the fact that your heart doesn’t start from zero; it starts from your resting rate. This generally gives you a more realistic picture of actual effort.
How to Measure Your Resting Heart Rate
Your resting heart rate is the foundation of the more accurate formula, so it’s worth getting right. The best time to measure it is in the morning before you get out of bed, or after you’ve been sitting calmly for several minutes.
Place two fingers (index and middle) on the inside of your wrist, just below the base of your thumb. Count the beats for 15 seconds and multiply by four. To improve accuracy, repeat this two more times and average the three readings.
A few things that throw off the measurement: don’t check within one to two hours of exercise or a stressful event. Wait at least an hour after caffeine, which can temporarily elevate your heart rate. And avoid measuring after you’ve been sitting or standing in one position for a long time, which can also skew the number. For most adults, a normal resting heart rate falls between 60 and 100 bpm, with fitter individuals often landing in the lower range.
Why Your Fitness Level Changes the Zones
The 220-minus-age formula is a population average. Not all 40-year-olds have the same actual maximum heart rate, and not all of them can sustain the same workload at a given percentage. Someone who’s been training consistently for years may have a true max that’s higher than the formula predicts, while someone just starting out may find that the lower end of their target zone already feels very hard.
This is why exercise physiologists often recommend starting at the bottom of your range and building up. The lower number in your target zone may actually be your practical ceiling when you’re beginning a new exercise routine. Over weeks and months, as your cardiovascular fitness improves, you’ll be able to sustain higher heart rates more comfortably, and your resting heart rate will likely drop, which shifts your Karvonen calculation as well.
Checking Intensity Without a Heart Rate Monitor
If you don’t have a chest strap or smartwatch, there’s a validated shortcut. The Borg Rating of Perceived Exertion is a scale from 6 to 20 where each number roughly corresponds to your heart rate divided by 10. A rating of 12 (moderate effort, you can talk but not sing) correlates to about 120 bpm. A 15 (hard effort, conversation is difficult) correlates to about 150 bpm.
The scale was originally designed with this heart rate correlation in mind, so it’s a useful cross-check. If you rate your effort at 13 or 14, you’re likely in a moderate-intensity zone. If you’re at 16 or 17, you’re solidly in vigorous territory. It’s not as precise as a monitor, but it’s surprisingly reliable for most people.
Signs You’re Pushing Too Hard
Exercising above 85% of your max heart rate isn’t inherently dangerous for healthy people, but there are warning signs worth knowing. Chest pressure, tightness, or pain during exertion is a red flag. So are unusual shortness of breath (beyond what you’d expect for the effort level), a racing or pounding heart that feels irregular, and lightheadedness. These warrant stopping the activity and getting evaluated.
A subtler signal: if your exercise performance or stamina drops noticeably over a short period and you haven’t changed your training habits, that can sometimes indicate an underlying cardiovascular issue rather than just a bad week. Anyone with a family history of sudden cardiac events, particularly in relatives younger than 60, should get a cardiac screening before starting intense training.