Your heart rate zones are five intensity ranges, each set as a percentage of your maximum heart rate. Zone 1 spans 50% to 60%, Zone 2 is 60% to 70%, Zone 3 covers 70% to 80%, Zone 4 runs from 80% to 90%, and Zone 5 is 90% to 100%. To turn those percentages into actual numbers, you first need to estimate your maximum heart rate, then do some simple math.
How to Find Your Maximum Heart Rate
The most common formula is 220 minus your age. If you’re 40, your estimated max is 180 beats per minute (bpm). It’s simple, but it was originally based on studies of men and carries a fair amount of individual variation.
A more refined formula, sometimes called the Tanaka formula, is 208 minus (0.7 × your age). For a 40-year-old, that gives 180 as well, but the two formulas diverge more at younger and older ages. In a study of 180 recreational marathon runners, the Tanaka formula produced a tighter spread of results, suggesting it may be slightly more consistent across individuals.
For women specifically, research led by cardiologist Martha Gulati produced a dedicated formula: 206 minus (0.88 × your age). The standard 220-minus-age formula was overestimating peak heart rate in many women, which skewed stress test results and made some women appear to have worse cardiac fitness than they actually did. A 40-year-old woman using the Gulati formula gets an estimated max of about 171 bpm, roughly 9 beats lower than the generic formula predicts.
Your Zones in Actual Numbers
Once you have your estimated max, multiply it by each zone’s percentage range. Here’s what that looks like for a 35-year-old using the 220-minus-age formula (max of 185 bpm):
- Zone 1 (50%–60%): 93–111 bpm. Light activity like walking or a gentle warm-up.
- Zone 2 (60%–70%): 111–130 bpm. A comfortable pace where you can hold a full conversation.
- Zone 3 (70%–80%): 130–148 bpm. Moderately hard effort, conversation becomes choppy.
- Zone 4 (80%–90%): 148–167 bpm. Hard effort you can sustain for only minutes at a time.
- Zone 5 (90%–100%): 167–185 bpm. All-out sprinting, sustainable for 30 seconds to a couple of minutes.
The American Heart Association frames it more broadly: moderate exercise falls at 50% to 70% of your max, and vigorous exercise at 70% to 85%. The five-zone model simply slices that range into finer segments so you can target specific training effects.
A More Personalized Calculation
The basic percentage method ignores your resting heart rate, which matters. Someone with a resting heart rate of 55 bpm is starting from a very different baseline than someone at 75 bpm. The heart rate reserve method (sometimes called the Karvonen method) accounts for this.
The steps are straightforward. First, find your heart rate reserve: subtract your resting heart rate from your maximum heart rate. Then multiply that reserve by the zone percentage you want, and add your resting heart rate back. So for a 35-year-old with a max of 185 and a resting rate of 60, the heart rate reserve is 125. To find the bottom of Zone 2 (60%), the math is (125 × 0.60) + 60 = 135 bpm. The top of Zone 2 (70%) would be (125 × 0.70) + 60 = 148 bpm.
Notice those numbers are higher than the simple percentage method gave for Zone 2 (111–130). That’s because the heart rate reserve approach accounts for the fact that your heart is already working at rest, so it sets a higher bar for each intensity level. Most exercise physiologists consider it the more accurate of the two methods.
What Each Zone Actually Does for You
Zone 1 is recovery territory. It promotes blood flow without adding training stress, making it useful for warm-ups, cool-downs, and easy days between harder sessions.
Zone 2 has attracted enormous attention in recent years. At this intensity, your body relies heavily on fat for fuel, depletes very little stored glycogen, and produces only modest amounts of metabolic byproducts. Blood lactate stays low, hovering around 1.5 to 2.0 millimoles per liter, just below the first lactate threshold. The case for Zone 2 as the foundation of endurance training is strong, but the popular claim that it’s uniquely powerful for building new mitochondria (the energy-producing structures in your cells) is more nuanced than often presented. Higher-intensity exercise actually creates a stronger signal for mitochondrial growth because it generates more of the metabolic stress that triggers those adaptations. Zone 2’s real advantage is that you can do a lot of it without breaking down, accumulating volume that builds aerobic fitness over weeks and months.
Zone 3 is sometimes called the “gray zone” because it’s hard enough to feel like real work but not intense enough to drive the same adaptations as Zone 4 or 5. It’s where many people default to during their runs or rides. It’s not harmful, but spending too much time here at the expense of truly easy or truly hard work can limit your progress.
Zone 4 sits right around your lactate threshold, the intensity where your body starts producing lactate faster than it can clear it. Training here improves your ability to sustain hard efforts for longer, which is why tempo runs and threshold intervals are staples for competitive athletes.
Zone 5 is maximal effort. Intervals in this range improve your body’s ceiling for oxygen use and its tolerance for high-intensity work. Sessions are short by necessity, typically lasting only a few minutes of total work time with recovery between efforts.
How to Test Your Zones Without a Lab
Formulas give you a starting point, but your actual zones may differ by 10 or more beats from the estimate. A simple field test can get you closer to reality. The 30-minute time trial, popularized by coach Joel Friel, is one of the most commonly used protocols. You go as hard as you can sustain for 30 minutes (running, cycling, or rowing), and your average heart rate over the final 20 minutes approximates your lactate threshold heart rate.
Once you have that number, you can anchor your zones around it rather than relying on a formula. Your lactate threshold typically falls near the boundary between Zone 3 and Zone 4 in the five-zone model, so knowing where it sits gives you a much more accurate map of your personal intensity ranges.
When Heart Rate Zones Don’t Work Well
Heart rate is influenced by more than effort. Caffeine, heat, dehydration, sleep deprivation, and stress can all push your heart rate higher at the same workload. On a hot day, you might see Zone 3 numbers while running at a Zone 2 pace.
Medications change the picture even more dramatically. Beta-blockers lower both resting and maximum heart rate, which makes standard zone calculations unreliable. If you take a beta-blocker, perceived exertion is a better guide. The Borg scale, which rates effort from 6 (no exertion) to 20 (maximum effort), provides a useful alternative. A rating of 12 to 14 corresponds roughly to moderate intensity, the equivalent of Zones 2 and 3.
Even without medication, perceived exertion is worth calibrating against your heart rate data. The simplest version: in Zone 2, you should be able to speak in full sentences. In Zone 3, you can manage a few words at a time. In Zone 4, talking is difficult. In Zone 5, it’s impossible. If your heart rate says Zone 2 but you’re gasping, trust your body over the number.
Putting It All Together
Start with your estimated max heart rate using the formula that fits you best (the standard 220-minus-age for a quick estimate, the Tanaka formula for a slightly refined version, or the Gulati formula if you’re a woman). If you know your resting heart rate, use the heart rate reserve method for more personalized zones. Then validate those numbers over a few weeks of training, paying attention to how different efforts feel relative to what your watch reports.
If you’re training for general fitness, the American Heart Association’s broad recommendation of 50% to 85% of your max covers the range you need. If you’re training for performance, the five-zone model gives you finer control, and a field test will sharpen your zones beyond what any formula can offer.