The Quick Answer
Heart rate training zones are defined intensity ranges based on a percentage of your maximum heart rate (MHR). The standard 5-zone model divides effort from easy recovery to all-out exertion.
Heart rate zone training is a cardiovascular exercise framework that uses heart rate as a proxy for exercise intensity.
The two most common ways to calculate zone boundaries are:
- Percentage of max HR: Zone boundary = MHR x percentage
- Karvonen formula: Zone boundary = Resting HR + (percentage x Heart Rate Reserve)
where Heart Rate Reserve (HRR) = Max HR - Resting HR.
The 5 Heart Rate Zones
| Zone | Name | % of Max HR | Feel | Typical duration | Primary benefit |
|---|---|---|---|---|---|
| 1 | Recovery | 50-60% | Very easy, conversational | 20-40 min | Active recovery, warm-up |
| 2 | Aerobic | 60-70% | Comfortable, can hold a conversation | 30-90 min | Fat oxidation, aerobic base |
| 3 | Tempo | 70-80% | Moderate, conversation becomes harder | 20-40 min | Aerobic capacity, efficiency |
| 4 | Threshold | 80-90% | Hard, can speak only a few words | 10-20 min intervals | Lactate threshold, speed |
| 5 | VO2max | 90-100% | Maximum effort, cannot talk | 30 sec - 3 min intervals | VO2max, anaerobic power |
Zone 2 has received significant attention in endurance training. Research on elite endurance athletes shows that many spend approximately 75-80% of their training time at low intensity (Zones 1-2) and the remainder at high intensity (Zones 4-5), with relatively little time in Zone 3.
How to Estimate Maximum Heart Rate
Age-predicted formula
The most widely used estimate:
Max HR = 220 - age
This formula originates from early exercise physiology research and was popularized by the American Heart Association. It is a population average with a standard deviation of approximately 10-12 bpm. Your true max could be meaningfully higher or lower.
Example: A 35-year-old has an estimated max HR of 220 - 35 = 185 bpm.
Alternative formulas
- Tanaka et al. (2001): Max HR = 208 - (0.7 x age). For a 35-year-old: 208 - 24.5 = 183.5 bpm.
- Gulati et al. (2010), women-specific: Max HR = 206 - (0.88 x age). For a 35-year-old woman: 206 - 30.8 = 175.2 bpm.
Field test
After a thorough 10-15 minute warm-up, run or cycle at maximal effort for 3-4 minutes (such as a steep hill sprint). The peak heart rate recorded is a practical estimate of your max. This should only be attempted by healthy individuals comfortable with all-out exertion.
Calculating Zones: Percentage of Max HR Method
This is the simpler of the two approaches. Multiply your max HR by the zone percentages.
Example: 35-year-old, Max HR = 185 bpm
| Zone | % Range | Calculation | BPM range |
|---|---|---|---|
| 1 | 50-60% | 185 x 0.50 to 185 x 0.60 | 93-111 |
| 2 | 60-70% | 185 x 0.60 to 185 x 0.70 | 111-130 |
| 3 | 70-80% | 185 x 0.70 to 185 x 0.80 | 130-148 |
| 4 | 80-90% | 185 x 0.80 to 185 x 0.90 | 148-167 |
| 5 | 90-100% | 185 x 0.90 to 185 x 1.00 | 167-185 |
The percentage-of-max method is quick but does not account for individual fitness. Two 35-year-olds with identical max HR but different resting heart rates will get the same zones, even though the fitter one (lower resting HR) has a larger working range.
Calculating Zones: The Karvonen Formula
The Karvonen method (Karvonen, Kentala, and Mustala, 1957) incorporates resting heart rate to personalize zones.
Formula: Target HR = Resting HR + (intensity % x Heart Rate Reserve)
where Heart Rate Reserve (HRR) = Max HR - Resting HR.
Worked example: 35-year-old, resting HR 65 bpm
Step 1: Max HR = 220 - 35 = 185 bpm
Step 2: Heart Rate Reserve = 185 - 65 = 120 bpm
Step 3: Calculate each zone boundary:
| Zone | % Range | Lower bound | Upper bound | BPM range |
|---|---|---|---|---|
| 1 | 50-60% | 65 + (0.50 x 120) = 125 | 65 + (0.60 x 120) = 137 | 125-137 |
| 2 | 60-70% | 65 + (0.60 x 120) = 137 | 65 + (0.70 x 120) = 149 | 137-149 |
| 3 | 70-80% | 65 + (0.70 x 120) = 149 | 65 + (0.80 x 120) = 161 | 149-161 |
| 4 | 80-90% | 65 + (0.80 x 120) = 161 | 65 + (0.90 x 120) = 173 | 161-173 |
| 5 | 90-100% | 65 + (0.90 x 120) = 173 | 65 + (1.00 x 120) = 185 | 173-185 |
Notice that the Karvonen zones are shifted higher compared to the simple percentage method. Zone 2, for instance, is 137-149 bpm (Karvonen) versus 111-130 bpm (percentage of max). This reflects the fact that the Karvonen method treats resting HR as the true "zero" of working effort.
Comparing the Three Approaches
| Method | Inputs needed | Personalization | Accuracy |
|---|---|---|---|
| % of Max HR (220 - age) | Age only | Low | +/- 10-12 bpm on max HR estimate |
| Karvonen (220 - age + resting HR) | Age + resting HR | Moderate | Better zone boundaries, same max HR limitation |
| Lab-tested max HR + Karvonen | Lab test + resting HR | High | Most accurate without lactate testing |
For most people, the Karvonen method using an age-predicted max HR is a practical balance of simplicity and accuracy. If you have access to a field test or lab test for max HR, using that measured value with Karvonen gives the most reliable zones.
How to Use Zones in Practice
Building an aerobic base (Zone 2 focus)
Most of your weekly training volume -- especially in the early stages of a fitness program or during a base-building phase -- should be in Zone 2. This intensity is sustainable, builds mitochondrial density, and improves fat oxidation. You should be able to hold a conversation throughout.
Interval training (Zones 4-5)
High-intensity intervals improve VO2max and lactate threshold. A common structure is 4 minutes at Zone 4 followed by 3 minutes at Zone 1-2, repeated 4-6 times. Zone 5 intervals are shorter: 30 seconds to 2 minutes at near-maximum effort with equal or longer rest periods.
The 80/20 guideline
A widely cited training distribution is 80% of sessions at low intensity (Zones 1-2) and 20% at high intensity (Zones 4-5). This polarized approach is supported by research on endurance athletes and is recommended by coaches such as Stephen Seiler and Matt Fitzgerald.
Recovery (Zone 1)
Zone 1 effort on rest days -- light walking, easy cycling -- promotes blood flow and recovery without adding training stress.
Frequently Asked Questions
Is Zone 2 training better for fat loss?
Zone 2 uses a higher percentage of fat for fuel, but higher zones burn more total calories per minute. For fat loss, total calorie deficit matters more than fuel source. Zone 2 is practical for fat loss because it allows long-duration sessions without excessive fatigue.
How do I find my max heart rate without a lab test?
Use 220 minus your age as a starting estimate. For a closer approximation, do a field test: after a thorough warm-up, run at maximum effort for 3-4 minutes and record your peak heart rate. Only do this if you are healthy and accustomed to intense exercise.
Why is my heart rate higher on some days?
Stress, sleep quality, hydration, caffeine, temperature, illness, and residual fatigue from prior training all affect heart rate. An elevated resting heart rate often signals that your body needs more recovery.
What is the Karvonen formula?
Target HR = Resting HR + (intensity % x Heart Rate Reserve), where Heart Rate Reserve = Max HR - Resting HR. It was published by Karvonen, Kentala, and Mustala in 1957 and produces more individualized zones than the simple percentage-of-max method.
Should I use a chest strap or a wrist-based monitor?
Chest straps are more accurate, especially during rapid heart rate changes in interval training. Wrist-based optical sensors have improved in recent years but can lag or produce artifacts during intense or irregular movements.
Can I do all my training in Zone 2?
Zone 2 alone builds aerobic endurance but does not adequately develop VO2max, lactate threshold, or speed. A mix of intensities -- predominantly low with some high-intensity work -- produces broader fitness adaptations.
How long should I train in each zone?
Zone 1: 10-20 min (warm-up/cooldown). Zone 2: 30-90 min. Zone 3: 20-40 min. Zone 4: 4-20 min of hard effort in intervals. Zone 5: 30 sec - 3 min bursts with rest between.
Is 220 minus age accurate?
It is a rough average with a standard deviation of about 10-12 bpm. Your actual max HR could differ significantly. It is a reasonable starting point but not a precision tool.
Why does my heart rate stay high after exercise?
Post-exercise heart rate gradually returns to baseline as your body clears metabolic byproducts and dissipates heat. Faster recovery to resting HR is generally associated with better cardiovascular fitness.
Do heart rate zones change as I get fitter?
Max HR stays relatively stable (it declines slowly with age, not with fitness). Resting HR typically decreases with improved fitness, which shifts your Karvonen zones. Recalculating every 2-3 months is reasonable.
Calculate Your Zones
Use the heart rate zones calculator to compute all 5 zones using either the percentage-of-max or Karvonen method. Enter your age and (optionally) your resting heart rate to see personalized zone boundaries.
For calorie estimation during zone-based training, try the calories burned calculator. To find your resting heart rate quickly, use the BPM tapper.