Heart Rate Zone Calculator

Heart rate zones give you a way to quantify how hard your cardiovascular system is working during exercise. Rather than running by feel or watching a clock, you run to a number. Each zone produces different physiological adaptations: lower zones build aerobic base and burn fat, higher zones improve VO2 max and lactate threshold. The Karvonen method improves on simple percentage-of-max-heart-rate calculations by accounting for your resting heart rate. Two people who are both 35 years old but have resting heart rates of 55 and 75 bpm have very different cardiovascular fitness levels. The Karvonen method gives them different target zones even though their max heart rates are the same. This calculator uses 220 minus age (the Astrand formula) to estimate max heart rate. This is a population average. Actual max heart rate can vary by 10 to 20 bpm in either direction. For precise zones, use a max heart rate measured in a graded exercise test rather than the estimate.

• Structuring a training week: Most endurance coaches recommend spending 80% of weekly training time in Zone 1-2 and 20% in Zone 3-4. Use your calculated zones to check whether your training is balanced or skewed toward high-intensity work.
• Fat burning and recovery runs: Zone 1 and low Zone 2 (50-65% of max using Karvonen) is where fat oxidation is highest relative to carbohydrate use. Recovery runs and easy long runs should stay in this range.
• Setting intensity for interval sessions: A structured interval might call for Zone 4 or Zone 5 effort. Your Karvonen-based targets tell you the exact bpm range to aim for during work intervals and confirm recovery is complete when HR drops back to Zone 1.
• Checking cardio equipment settings: Many treadmills and cardio machines have preset heart rate targets. Entering the Karvonen-based zone boundaries into the machine instead of relying on its default calculations gives you a more accurate target.

• Using a formula-based max HR when actual is very different: The 220 minus age formula has a standard deviation of about 10-12 bpm. If you have ever hit 195 bpm at age 35, your actual max is near 195, not 185. Use a tested maximum for precise zones.
• Measuring resting HR after activity: Resting HR should be measured after a full night of sleep, before caffeine, and before significant physical activity. Measuring it after a morning jog or two cups of coffee inflates the number and compresses your calculated zones.
• Spending too much time in Zone 3: Zone 3 is often called the "junk zone." It is hard enough to cause fatigue but not intense enough to produce the full adaptations of Zone 4-5 work. Many recreational runners default to Zone 3 for most runs, which limits both easy-day recovery and hard-day gains.
• Ignoring zone drift during long sessions: Heart rate rises over time at constant effort (cardiac drift) due to dehydration and heat. A run that starts in Zone 2 may drift to Zone 3 after an hour. Monitoring HR throughout a long run prevents unplanned high-zone accumulation.

1. 1Enter your age. The calculator estimates your maximum heart rate as 220 minus your age.
2. 2Enter your resting heart rate, measured first thing in the morning before getting out of bed for best accuracy.
3. 3Select your training intensity: light (50-60%), moderate (60-70%), vigorous (70-85%), or maximum (85-95%).
4. 4The calculator finds your heart rate reserve: max heart rate minus resting heart rate.
5. 5It applies the Karvonen formula to each zone boundary: (reserve × percentage) + resting HR.
6. 6All five zones are shown, plus the specific target range for your chosen intensity.

• Measure resting HR over several mornings: A single measurement can be influenced by stress, sleep quality, or illness. Average three to five consecutive morning readings for a more stable resting HR value to enter here.
• Use a chest strap for reliable zone training: Wrist-based optical HR sensors lag by 10-30 seconds during intensity changes and can underread at high effort. For interval training where you need to know your zone in real time, a chest strap gives more responsive and accurate data.
• Retest resting HR every few months: As fitness improves, resting HR typically drops. Updating the value in this calculator shifts all your zones downward, which reflects the expanded reserve you have developed.
• Check against perceived effort: At Zone 2 you should be able to hold a conversation. At Zone 4, speaking in sentences is difficult. If your calculator says Zone 2 but you cannot speak, your actual max HR is probably higher than 220 minus your age.