The simplest way to estimate your maximum heart rate is to subtract your age from 220. A 40-year-old gets an estimate of 180 beats per minute (bpm). But this formula has a standard deviation of about 11 bpm, meaning your true max could easily be 10 or more beats higher or lower than what the math suggests. If you need a more reliable number, you have better options.
Why the 220-Minus-Age Formula Falls Short
The “220 minus age” equation traces back to a 1971 paper by Fox and colleagues, but it wasn’t based on original research. It was derived from a collection of earlier observations and has stuck around largely because it’s easy to remember. The American College of Sports Medicine notes that all prediction equations carry an error range of 3 to 12 bpm, which makes every formula a rough estimate rather than a precise measurement.
For most people using heart rate zones in casual fitness, that margin of error is fine. But if you’re training seriously, adjusting medication, or using heart rate to monitor a health condition, a 10 to 20 bpm gap between your estimated and actual max can throw off every target zone you calculate from it.
A Better Formula for Women
The 220-minus-age equation was built mostly on male data, and it consistently overestimates maximum heart rate in women. Research published in Circulation by Dr. Martha Gulati and colleagues developed a sex-specific formula from a study of over 5,000 asymptomatic women: 206 minus (0.88 × age). For a 40-year-old woman, that gives a max of about 171 bpm instead of 180.
The difference matters more than it sounds. In the study, 25% of women exceeded 100% of the max predicted by the traditional formula, which seems impossible unless the formula itself is wrong for that population. Meanwhile, using the traditional number caused twice as many women to be falsely classified as unable to reach their target heart rate during stress testing. If you’re a woman using heart rate zones, the Gulati formula is a better starting point.
How to Test Your Max With a Field Test
A self-guided field test gives you a real measured number instead of an estimate. You’ll need a heart rate monitor (a chest strap is more reliable than a wrist sensor for peak efforts), a hill that takes at least two minutes to climb, and ideally a training partner nearby for safety.
Here’s a straightforward hill protocol:
- Warm up for 15 minutes on flat ground, gradually building to your normal training pace.
- First hill effort: Run up the hill for at least two minutes, building to a pace you estimate you could sustain for 20 minutes. You don’t need to actually hold it that long. Jog back down to recover.
- Second hill effort: Run up the hill again, this time pushing to a faster pace. Near the top, give a hard final surge. The highest reading on your monitor during or just after this effort is close to your maximum heart rate.
This type of test requires you to be in reasonable cardiovascular shape and comfortable with high-intensity effort. If you haven’t exercised at high intensity before, or you have any known heart conditions, a clinical test is the safer route.
Clinical Stress Testing
The gold standard is a graded exercise test in a medical setting. The most widely used version, called the Bruce protocol, puts you on a treadmill that gets progressively steeper and faster across seven three-minute stages. By the final stage, you’d be walking at 5.5 mph up a 20% grade, though most people stop well before that.
Throughout the test, adhesive pads on your chest feed data to an electrocardiograph that tracks your heart’s electrical activity in real time. A blood pressure cuff checks your readings every few minutes, and a clinician watches both the monitor and you for signs of distress. The goal is typically to push your heart to at least 85% of its predicted capacity. After the test, you cool down with slow walking and then sit quietly for about 15 minutes while your heart rate returns to baseline.
This isn’t something you’d schedule just to find your training zones. Stress tests are usually ordered to evaluate symptoms like chest pain, shortness of breath, or irregular heartbeats. But if you’re on medications that affect heart rate, or you have risk factors that make a high-intensity field test unwise, a clinical test gives you the most accurate number under safe conditions.
How Medications Change the Picture
Beta-blockers, commonly prescribed for high blood pressure and certain heart conditions, slow your heart rate and prevent it from climbing the way it normally would during exercise. If you take a beta-blocker, the 220-minus-age formula becomes essentially useless because your heart physically cannot reach that predicted number.
There’s no simple adjustment factor to account for the drug’s effect. The Mayo Clinic recommends two alternatives: getting an exercise stress test to find your actual medicated maximum, or skipping heart rate altogether and using a perceived exertion scale instead. The Borg Rating of Perceived Exertion scale has you rate how hard you feel you’re working on a numerical scale, based on your breathing, fatigue, and effort level. It bypasses the heart rate question entirely and can be a more reliable guide when medications are in play.
Wrist Sensors and Their Limits at Peak Effort
Optical heart rate sensors on smartwatches have gotten better in recent years, but they still struggle at the exact moment accuracy matters most: during peak exertion. Wrist-based readings tend to lag behind actual heart rate by a second or more during rapid changes, which is precisely what happens when you’re sprinting uphill trying to find your max. During high-intensity interval work, the ramp-up delay can mean you miss your true peak entirely.
The sensors are also sensitive to how snugly the watch sits and how much your wrist is moving. Bouncing or arm-swinging can throw readings off by 10 bpm or more. If you’re doing a field test to find your maximum heart rate, a chest strap monitor will give you a significantly more accurate reading than any wrist-worn device.
Putting Your Number to Use
Once you have a maximum heart rate, whether estimated or measured, you can calculate training zones as percentages of that number. A common framework breaks effort into five zones: recovery (50 to 60% of max), aerobic base (60 to 70%), tempo (70 to 80%), threshold (80 to 90%), and maximum effort (90 to 100%). The specific percentages vary slightly depending on the system, but the concept is the same.
Keep in mind that your maximum heart rate is not a fitness indicator. It doesn’t improve with training, and a higher max doesn’t mean a healthier heart. It’s largely determined by genetics and decreases naturally with age. Two equally fit people of the same age can have maximums that differ by 20 bpm or more. What matters for fitness is what your heart can do at submaximal effort: how much work you can sustain at 70% or 80% of your max, and how quickly your heart rate recovers after hard efforts. Your max is just the anchor point that makes those percentages meaningful.