What this calculates
Heart rate training zones divide your cardiovascular effort into distinct intensity bands, each targeting different physiological adaptations. This calculator implements two methods: the Karvonen method (using heart rate reserve) and the simpler percentage of maximum heart rate (%HRmax) method.
The Karvonen method, published by Martti Karvonen in 1957, accounts for your resting heart rate when calculating training intensity. The formula is: target HR = ((HRmax − HRrest) × intensity%) + HRrest. The gap between your max and resting heart rate — the heart rate reserve — scales your actual training zones. Two runners with the same maximum heart rate but different resting heart rates (say, 45 bpm vs 65 bpm) will train at different absolute heart rates even at the same relative intensity.
The %HRmax method is simpler: zones are defined as fixed percentages of your maximum heart rate, with the resting heart rate ignored. The ACSM guidelines define the five zones as: Zone 1 (50–60%), Zone 2 (60–70%), Zone 3 (70–80%), Zone 4 (80–90%), Zone 5 (90–100%). This is the method most common in fitness trackers and general-purpose heart rate monitors.
For serious training, the Karvonen method is more individualised and more accurate in capturing true physiological intensity. For casual use or when you don't know your resting heart rate, the %HRmax method is a reasonable approximation.
Max heart rate is typically estimated using 220 − age (the Fox formula), though this formula has poor accuracy at the individual level — standard deviation is approximately ±10–12 bpm. The Tanaka formula (208 − 0.7 × age) is slightly more accurate for older adults. Measured max HR from a proper max test is always preferred.
How to use this calculator
Enter your age and, if you know it, your resting heart rate (measured in the morning before getting up). You can also enter a directly measured maximum heart rate if you have one from a race or max effort test.
The calculator shows both Karvonen and %HRmax zones side by side. For each zone, you'll see the heart rate range and a brief description of the physiological purpose of training at that intensity.
If you don't know your max heart rate: the calculator uses 220 − age as a default. This is a population average — your actual max may be 10–15 bpm higher or lower. For accurate zones, do a proper max HR test (a race or a 20-minute all-out effort on a flat course, finishing with a sprint).
Methodology
Karvonen method: target HR = ((HRmax − HRrest) × intensity%) + HRrest, from Karvonen et al. (1957), "The effects of training on heart rate." Zone boundaries: Z1 50–60%, Z2 60–70%, Z3 70–80%, Z4 80–90%, Z5 90–100% of heart rate reserve. %HRmax method: zone boundaries at 50, 60, 70, 80, 90, 100% of HRmax per ACSM guidelines. Default HRmax estimation: 220 − age (Fox formula).
Full methodology and formula sources →
Frequently asked questions
Which method should I use — Karvonen or %HRmax?
Karvonen is more individualised and better for serious training. It accounts for cardiovascular fitness via resting heart rate. %HRmax is simpler and works fine for casual training or when you don't know your resting HR. If in doubt, use Karvonen.
How do I find my maximum heart rate?
The formula 220 − age is a rough population average with large individual variation (±10–12 bpm). For accurate zones, measure your max HR in a race (where you're physiologically and competitively motivated to push) or via a structured max test: warm up 10 minutes, then run 3 × 1-minute hard efforts with 1-minute jogs, recording peak HR.
What is resting heart rate and how do I measure it?
Resting heart rate is your heart rate when fully at rest. Measure it first thing in the morning before getting out of bed. Lie still for 60 seconds and count beats, or use a heart rate monitor. Average over 3–5 mornings for a reliable number. Typical range for trained runners: 40–65 bpm.
Why do different devices show different zone numbers?
Different manufacturers use different formulas. Garmin uses %HRmax with different zone boundaries than Polar; Apple Watch uses a different model. This calculator uses ACSM guidelines for %HRmax and the Karvonen 1957 paper. The numbers will differ from your device if it uses a different definition.
What is Zone 2 running and why is it popular?
Zone 2 (60–70% of HRmax or 60–70% of heart rate reserve) corresponds to aerobic base training — a comfortable effort where you can sustain a conversation. Research by Seiler, Maffetone, and others suggests a large proportion of training volume at this intensity builds the aerobic base efficiently while minimising injury risk and recovery cost.