Target Heart Rate Calculator
Get every training zone personalized to your fitness. Enter your age and resting heart rate, pick a max-HR formula (Fox, Tanaka, or Nes), and the calculator returns all five zones in beats per minute using the Karvonen heart-rate reserve method. Set a custom intensity range for your workout or use the full zone breakdown table.
Formula
Worked example
Age 30, resting HR 65, Fox formula: max HR = 220 - 30 = 190; reserve = 190 - 65 = 125. Zone 3 (70-80% Karvonen): lower = 125 x 0.70 + 65 = 152 bpm; upper = 125 x 0.80 + 65 = 165 bpm. Reverse: if your HR is 145 bpm, intensity = (145 - 65) / 125 = 64% = Zone 2 aerobic base.
How the three max-HR formulas differ
The classic Haskell and Fox formula (220 minus age, published 1971) is the most widely used because it is simple and printed on most gym equipment. Its main limitation is a standard deviation of about 10-12 bpm, so your true maximum could be noticeably higher or lower. The Tanaka formula (208 minus 0.7 times age, published 2001) is based on a meta-analysis of 351 studies and tends to give slightly higher estimates for older adults, making it more accurate for people over 40. The Nes formula (211 minus 0.64 times age, published 2013) was derived from a large Norwegian population study and also corrects for the Fox formula's tendency to underestimate max HR in older, active individuals. For most recreational exercisers Fox is fine; endurance athletes and anyone over 40 may benefit from switching to Tanaka or Nes.
Karvonen vs. percentage of max HR
Gym treadmills and AHA charts typically calculate heart-rate zones as a flat percentage of your estimated maximum, for example 70% of max HR. The Karvonen method (also called the heart-rate reserve method) subtracts your resting heart rate first, so it accounts for your current fitness level. A trained athlete with a resting HR of 45 bpm will have a larger reserve than a beginner with a resting HR of 75 bpm, even at the same age, so Karvonen gives them genuinely different zones. Research consistently shows Karvonen zones align more closely with measured oxygen consumption during exercise, which makes them more useful for training prescription. The % of max HR method is simpler and perfectly adequate for general fitness guidance.
Understanding the five training zones
Zone 1 (50-60%) is light recovery work: the body burns mostly fat and the cardiovascular system experiences minimal stress. Zone 2 (60-70%) is the aerobic base zone, the workhorse of endurance training. Long slow distance runs, easy cycling, and brisk walking typically land here. This zone improves mitochondrial density and fat oxidation, the two pillars of endurance. Zone 3 (70-80%) is tempo work, conversational but not comfortable. Zone 4 (80-90%) pushes above the lactate threshold, where lactate begins to accumulate faster than it is cleared. High-intensity interval training (HIIT) targets this zone. Zone 5 (90-100%) is maximal effort: sprints, max-effort hill repeats, and short track intervals. It is highly stressful and should represent a small fraction of total weekly training.
Using the reverse-solve mode
The reverse mode lets you enter the heart rate you are actually hitting during a workout and find out which intensity zone that corresponds to. This is useful when you are using a heart-rate monitor and want to know whether your current effort matches your training plan. Enter the heart rate shown on your watch or chest strap, choose the same formula and method you used when setting up your plan, and the calculator tells you the percentage intensity and zone name. If your HR is drifting higher than the target zone during a long run, it could indicate dehydration, heat stress, or accumulated fatigue, all good reasons to back off.
Training zones by % of heart-rate reserve (Karvonen)
| Zone | % HRR | Effort feel | Trains | Weekly volume |
|---|---|---|---|---|
| 1: Recovery | 50-60% | Very easy, can hold a full conversation | Active recovery, fat use | 10-20% |
| 2: Aerobic base | 60-70% | Easy, can speak in full sentences | Endurance, mitochondria | 40-50% |
| 3: Tempo | 70-80% | Moderate, short sentences only | Aerobic capacity | 20-25% |
| 4: Threshold | 80-90% | Hard, few words at a time | Lactate threshold, speed | 10-15% |
| 5: Maximal | 90-100% | Maximal, cannot speak | VO2 max, peak power | 5% |
Intensity ranges, what each zone develops, and recommended weekly volume distribution.
Frequently asked questions
Which max-HR formula should I use?
For most people, the classic Fox formula (220 minus age) is accurate enough. If you are over 40 or a regular endurance athlete, the Tanaka or Nes formulas tend to be more accurate because they account for the fact that max HR does not decline as steeply with age in fitter individuals. If you have had a recent supervised maximal exercise test, use that result rather than any formula.
What is the difference between Karvonen and % of max HR?
The Karvonen formula uses heart-rate reserve (max HR minus resting HR) to personalize your zones. Because it factors in your resting heart rate, two people of the same age get different zones based on their fitness. Percentage of max HR skips that step and is simpler but less personalized. Karvonen zones align better with measured exercise intensity (VO2) and are preferred for structured training plans.
How do I measure my resting heart rate accurately?
Measure it first thing in the morning before getting out of bed, ideally after at least seven hours of sleep. Count your pulse for 60 seconds, or 30 seconds and double it. Do this on three or four consecutive days and average the readings, since factors like caffeine, stress, and poor sleep can temporarily raise the number.
Is 220 minus age accurate for everyone?
It is a population average with a standard deviation of about 10-12 bpm, so your true maximum could be anywhere from 10-12 bpm higher or lower. Studies have shown it consistently underestimates max HR in older and fitter individuals. For precision, a supervised graded exercise test (GXT) on a treadmill or cycle ergometer is the only reliable method.
What does the reverse-solve mode tell me?
Enter the heart rate you are hitting during a workout and the calculator tells you what percentage intensity that corresponds to and which of the five training zones you are in. This helps you confirm whether your effort matches your training plan, and it works with both the Karvonen and % of max HR methods.
How much time should I spend in each zone?
Research on elite endurance athletes and recreational runners consistently supports a polarized distribution: about 75-80% of weekly volume in Zone 1-2 (low intensity) and 20-25% in Zone 4-5 (high intensity), with relatively little time in Zone 3. For general health, the American Heart Association recommends at least 150 minutes per week of moderate-intensity activity (roughly Zone 2) or 75 minutes of vigorous activity (Zone 4).