Zone 2 has become one of the most talked-about ideas in endurance training: long, easy sessions at a conversational effort that build the aerobic engine without leaving you too tired to train again tomorrow. The idea is simple, but the practical question is how fast the heart should be beating. The honest answer is that there is no single definition, and heart rate is only one way to judge the effort. This calculator gives you three reference ranges from your age and resting heart rate, and explains where each comes from.
Treat these as starting estimates. The best check of your own zone 2 is how it feels: relaxed, nose-breathing or full sentences, with no strain.
How to use the zone 2 heart rate calculator
- Enter your age and pick a maximum heart rate formula.
- Add your resting heart rate if you have it, to see the heart-rate-reserve range.
- Compare the three ranges. The 60–70% convention is the usual “zone 2”; the ACSM band is a slightly higher moderate range; the reserve method personalises it.
- Test it by feel. You should be able to hold a conversation. If you cannot, ease off.
Zone 2 heart rate formulas
Zone 2, common convention: 60% to 70% of maximum heart rate
ACSM moderate band: 64% to 76% of maximum heart rate
Heart rate reserve band: resting + (40% to 59%) × (max − resting)
“Zone 2” in the five-zone scheme used by many watches and coaches is 60 to 70 percent of maximum heart rate; this is a convention rather than a published physiological standard. The ACSM bands (moderate intensity 64–76 percent of maximum heart rate, or 40–59 percent of heart rate reserve) come from ACSM’s Guidelines for Exercise Testing and Prescription. Maximum heart rate formulas are from Fox et al. (1971) and Tanaka et al. (J Am Coll Cardiol 2001;37:153–156).
Worked example
A 35-year-old with a resting heart rate of 55 bpm.
- Maximum heart rate = 220 − 35 = 185 bpm
- Common zone 2: 0.60 × 185 to 0.70 × 185 = 111 – 130 bpm
- ACSM moderate: 0.64 × 185 to 0.76 × 185 = 118 – 141 bpm
- Heart rate reserve = 185 − 55 = 130, so 55 + 0.40 × 130 to 55 + 0.59 × 130 = 107 – 132 bpm
Zone 2 ranges by age
| Age | Max HR (220 − age) | Zone 2, common convention (60–70%) | ACSM moderate band (64–76%) |
|---|---|---|---|
| 20 | 200 | 120 – 140 | 128 – 152 |
| 30 | 190 | 114 – 133 | 122 – 144 |
| 40 | 180 | 108 – 126 | 115 – 137 |
| 50 | 170 | 102 – 119 | 109 – 129 |
| 60 | 160 | 96 – 112 | 102 – 122 |
| 70 | 150 | 90 – 105 | 96 – 114 |
Heart rate is only an estimate
- Maximum heart rate varies. The standard deviation around the age-based formulas is about 10 bpm, so two 40-year-olds can have maxima 20 beats apart.
- Conditions change the number. Heat, caffeine, poor sleep, altitude and illness raise heart rate at the same effort.
- Medicines matter. Beta blockers and some other drugs lower heart rate, so these ranges do not apply.
- Use the talk test. If you can speak in full sentences you are almost certainly at or below zone 2.
Putting zone 2 to use
Many endurance programmes spend most of their weekly time at low intensity and a smaller share at high intensity. A common approach is to start with two or three easy sessions of 30 to 60 minutes and build duration before adding speed. For the full set of zones see the Target Heart Rate Calculator; for pacing use the Running Pace Calculator; and for an estimate of effort in calories try the Calories Burned Running Calculator. If you want a fitness benchmark, the VO2 Max Calculator estimates aerobic capacity.
This page is for information only and is not medical advice. If you have a heart condition, take medicines that affect heart rate, or are new to exercise, check with a doctor before starting a training plan.
Sources
- American College of Sports Medicine. ACSM’s Guidelines for Exercise Testing and Prescription, 11th edition, 2021 (intensity classification).
- Tanaka H, Monahan KD, Seals DR. Age-predicted maximal heart rate revisited. J Am Coll Cardiol 2001;37:153–156.
- Fox SM, Naughton JP, Haskell WL. Ann Clin Res 1971;3:404–432.
- Persinger R, Foster C, Gibson M, Fater DC, Porcari JP. Consistency of the talk test for exercise prescription. Med Sci Sports Exerc 2004;36:1632–1636.
Frequently asked questions
What is zone 2 training?
Zone 2 is the second of five commonly used heart rate zones: an easy, steady aerobic effort at which you can hold a conversation. Coaches use it to build aerobic endurance because it can be done for long periods with limited fatigue.
Is there an official definition of zone 2?
Not one that all bodies share. The “60 to 70 percent of maximum heart rate” band is a convention used by many coaches and wearable makers. Exercise science uses other schemes, such as the three-zone model and the American College of Sports Medicine intensity categories. The calculator shows the convention and the ACSM moderate band so you can compare.
How do I know I am in zone 2 without a monitor?
Use the talk test: you should be able to speak in full sentences while breathing a little harder than normal. The talk test has been validated against ventilatory thresholds (Persinger et al., Med Sci Sports Exerc 2004;36:1632–1636). If you can only say a few words, you are above zone 2.
How long and how often should I train in zone 2?
There is no single prescription. Many endurance athletes do the majority of their weekly volume at low intensity, while health guidance asks adults for at least 150 minutes of moderate activity a week. Build up gradually if you are new to exercise.
Why does my heart rate drift up on long sessions?
Heat, dehydration and fatigue raise heart rate for the same pace (cardiac drift). If you drift above your range, slow down rather than holding pace, and drink and cool as needed.