Karvonen Formula Calculator
The Karvonen formula uses your heart rate reserve (maximum heart rate minus resting heart rate) to calculate personalised training zones. Because it accounts for your individual fitness level, it gives more accurate target heart rates than a simple percentage of maximum heart rate. Enter your resting heart rate and maximum heart rate (or your age for an estimate) and all five training zones update instantly.
Formula
Worked example
A 35-year-old with a resting HR of 65 bpm and an estimated max HR of 185 bpm (220 - 35) has a heart rate reserve of 120 bpm. At 70% intensity: (120 x 0.70) + 65 = 84 + 65 = 149 bpm. Zone 2 (60-70%) runs from 137 to 149 bpm.
What is the Karvonen formula?
The Karvonen formula, developed by Finnish physiologist Martti Karvonen in 1957, calculates a target heart rate by using your heart rate reserve (HRR), which is the difference between your maximum heart rate and your resting heart rate. The formula is: Target Heart Rate = (HRR x Intensity %) + Resting Heart Rate. By factoring in your resting heart rate, the formula accounts for your current cardiovascular fitness level. A highly trained athlete with a low resting heart rate will get different zone boundaries than a sedentary beginner, even if both are the same age and have the same maximum heart rate. This makes it significantly more personalised than the older, simpler method of taking a straight percentage of maximum heart rate.
How to find your maximum heart rate
This calculator offers three options. The most common estimate uses the Fox formula: 220 minus your age. For adults over 40, the Tanaka formula (208 - 0.7 x age) has been shown to be more accurate in studies. For the most precise zones, you can enter a measured maximum heart rate from a supervised field test or graded exercise test. Estimated formulas can be off by as much as 10-12 bpm for any individual, so if precision matters for your training, a proper max-HR test is worthwhile.
The five training zones explained
Zone 1 (50-60% HRR) is active recovery. Your body can clear lactate faster than it is produced, making it ideal for warm-ups, cool-downs, and easy recovery days. Zone 2 (60-70% HRR) is the aerobic base zone. Mitochondria density and fat metabolism improve most here, and most elite endurance athletes do roughly 80% of their volume in this zone. Zone 3 (70-80% HRR) is the aerobic threshold zone, roughly marathon or tempo pace. Zone 4 (80-90% HRR) is the anaerobic zone, the intensity of interval workouts and 5K to 10K race pace. Zone 5 (90-100% HRR) is maximum effort, used for short sprint intervals. Spending too much time in Zones 3 and 4 without adequate Zone 1-2 volume is one of the most common training mistakes.
Karvonen vs. simple percentage of max HR
The older method of setting training zones uses a flat percentage of maximum heart rate. For example, 70% effort is simply 0.70 x max HR. The Karvonen method adjusts for resting heart rate, which means the effective intensity of any given percentage is matched to the individual. Consider two people with the same max HR of 190 bpm. If one has a resting HR of 40 bpm and the other has 75 bpm, the 70% Karvonen target will be 159 bpm for the fit person but 153 bpm for the unfit one. This difference reflects the gap in their cardiovascular efficiency and means each person is working at a truly equivalent relative intensity. Research suggests this makes the Karvonen method a better predictor of oxygen consumption and perceived effort across fitness levels.
Five-zone Karvonen training zones
| Zone | Name | % of HRR | Perceived Effort | Primary Benefit |
|---|---|---|---|---|
| 1 | Recovery | 50-60% | Very easy | Active recovery, fat metabolism |
| 2 | Aerobic Base | 60-70% | Comfortable | Aerobic endurance, fat burning |
| 3 | Aerobic Threshold | 70-80% | Moderately hard | Tempo fitness, lactate threshold |
| 4 | Anaerobic | 80-90% | Hard | VO2max, speed endurance |
| 5 | Maximum Effort | 90-100% | All out | Peak power, sprint capacity |
Standard five-zone model using the Karvonen heart rate reserve method. Your personalised bpm ranges are shown in the zone table above.
Frequently asked questions
How accurate is the 220 minus age formula?
The 220 - age formula is a population average with a standard deviation of about 12 bpm, so for any individual it can be meaningfully off. The Tanaka formula (208 - 0.7 x age) performs slightly better, particularly for adults over 40. For the most accurate zones, measure your actual maximum heart rate during a supervised all-out effort or graded exercise test. If you have only ever estimated your max HR, treat your calculated zones as a starting point and adjust based on how the effort actually feels.
What is heart rate reserve?
Heart rate reserve (HRR) is the difference between your maximum heart rate and your resting heart rate. It represents the working range available to your cardiovascular system. A large HRR is generally associated with good cardiovascular fitness. The Karvonen formula expresses training intensity as a percentage of HRR rather than a percentage of max HR, which makes the zones more responsive to individual fitness differences.
Why is my Zone 2 heart rate so high compared to what I expected?
If you have a low resting heart rate (common in trained athletes), the Karvonen formula will push all your zone boundaries upward compared to the simple percentage method. This is intentional and correct. A low resting HR reflects a stronger heart that pumps more blood per beat, so you need a higher absolute heart rate to achieve the same relative cardiovascular stress. The Karvonen zones reflect this reality better than flat percentage methods.
How do I measure my resting heart rate accurately?
Measure first thing in the morning before getting up, after at least five minutes lying still. Count your pulse for a full 60 seconds, or use a finger on your wrist or neck and count for 30 seconds then double it. For the most reliable number, take readings on three or more mornings and average them. Illness, alcohol, dehydration, stress, and poor sleep can all elevate your resting HR, so readings on those days will not be representative.
Should I train in Zone 2 most of the time?
For most endurance athletes and general fitness goals, the answer is yes. Research on elite athletes consistently shows that 75-85% of training volume is done at low intensity (Zones 1 and 2), with the remaining 15-25% at high intensity (Zones 4 and 5). The mistake most recreational athletes make is spending too much time at moderate intensity (Zone 3), which is hard enough to cause fatigue but not intense enough to drive the strongest adaptations. This is sometimes called the "polarised" or "80/20" training model.
Can I use the Karvonen formula for weight loss?
Yes. Zone 2 (60-70% HRR) is sometimes called the "fat-burning zone" because at that intensity the body preferentially metabolises fat for fuel. However, fat loss ultimately depends on total caloric expenditure over time. Higher-intensity zones burn more calories per minute, even if a smaller proportion comes from fat. For sustainable fat loss, a combination of Zone 2 volume and some higher-intensity work tends to work better than any single zone alone.
Does the Karvonen formula apply to cycling and swimming too?
The formula itself applies to any aerobic activity, but your maximum and resting heart rate may differ between modalities. Maximum cycling HR is typically 5-10 bpm lower than running HR, and swimming HR is lower again. For the most accurate zones in each sport, measure a sport-specific max HR rather than assuming a single value applies across all activities.