How the Zone 2 calculator works
Zone 2 training is the foundation of endurance development, and this calculator gives you the heart rate ceiling for it using whichever inputs you have. The MAF formula subtracts your age from 180 and applies a fitness modifier, producing a conservative 10-beat band. The percent of max method takes 60 to 70 percent of your estimated maximum heart rate, calculated with the Tanaka formula (208 minus 0.7 times age). The Karvonen method is more personalized: it takes 60 to 70 percent of your heart rate reserve (max minus resting) and adds it back on top of your resting heart rate, so two runners of the same age with different resting heart rates get different zones. If you know your true max heart rate from a race finish or lab test, the fourth method uses it directly for the most accurate zones.
When to use this calculator
Use it to set the ceiling for easy runs, long runs, and recovery days, which should make up 70 to 80 percent of your weekly running. The most common mistake in endurance training is running easy days too hard: hard enough to accumulate fatigue, not hard enough to force adaptation. A concrete heart rate number on your watch removes the guesswork. Recheck your zones every few months, or whenever your resting heart rate changes meaningfully, since aerobic fitness moves the Karvonen numbers.
Worked example
Take a 40-year-old runner with a resting heart rate of 55. The MAF formula with no modifier gives a range of 130 to 140 bpm. The percent of max method estimates max heart rate at 180 and puts Zone 2 at 108 to 126 bpm. Karvonen splits the difference: heart rate reserve is 125, so the zone is 130 to 143 bpm. The spread between methods is normal; they draw the line in different places. Pick one method, note the range, and stay consistent with it so your training data means something over time.
Method selection advice
- MAF: best for runners returning from injury or building a first base. Conservative by design, and its modifiers account for training history.
- Percent of max HR: simplest inputs, reasonable default when all you know is your age.
- Karvonen: more personalized, and it responds to fitness because your resting heart rate drops as you get fitter.
- Karvonen with known max: the most accurate option here. A true max from a hard race finish beats any age formula.
Whichever method you choose, the conversation test is the final arbiter: in Zone 2 you can speak in full sentences. If you can only manage a few words at a time, you are above it, whatever the watch says.
Frequently asked questions
What is Zone 2 heart rate?
Zone 2 is the intensity band just below your first ventilatory threshold, roughly 60 to 70 percent of your maximum heart rate. At this effort your body relies mostly on fat for fuel and you can speak in full sentences. It is the intensity that builds mitochondrial density and aerobic capacity with minimal fatigue cost, which is why most successful endurance programs spend the majority of training time there.
Which Zone 2 calculation method should I use?
If you know your actual maximum heart rate from a recent all-out effort or lab test, use the Karvonen method with that number; it is the most personalized. If you know your resting heart rate but not your max, use the standard Karvonen method. The MAF formula is a good conservative starting point for runners building a base, and percent of max HR is the simplest if you only know your age.
Why is my Zone 2 pace so slow?
If you have trained mostly at moderate or hard intensities, your aerobic system is underdeveloped relative to your legs, and staying in Zone 2 may initially mean very slow running or even walk breaks on hills. That is normal and it is exactly the signal that Zone 2 work will help. Most runners see their pace at the same heart rate improve within 8 to 12 weeks of consistent aerobic volume.
How much of my training should be in Zone 2?
A common and well-supported distribution is roughly 80 percent of weekly running at easy aerobic intensity and 20 percent at moderate to hard intensity. For most runners that means easy runs, long runs, and recovery days all sit in Zone 2, with one or two quality sessions per week above it.
Is the 220 minus age formula accurate for max heart rate?
It is the best-known formula but not the most accurate. This calculator uses the Tanaka formula (208 minus 0.7 times age), which was derived from a larger dataset and drifts less at older ages. Even so, any age-based estimate can miss your true max by 10 or more beats per minute, which is why a field-tested max heart rate gives better zones.