Heart Rate Zone Calculator

The calculator uses the simplest reliable estimate of maximum heart rate: 220 minus your age. So a 35-year-old has an estimated max HR of 185 bpm. From there it splits the range into five zones at 50/60/70/80/90% intensity: Recovery (50-60%), Fat Burn (60-70%), Aerobic (70-80%), Anaerobic (80-90%) and VO2 Max (90-100%). Each zone has a different physiological purpose, and structuring training around them is what separates polarised training from grinding away at one pace forever.

There is also a Karvonen toggle, which is more accurate. Karvonen takes your heart rate reserve (max HR minus resting HR) and applies the zone percentages to the reserve, then adds back the resting figure. For the same 35-year-old with a resting HR of 60, the aerobic zone via 220-age is 130-148 bpm; via Karvonen it is 148-160. Karvonen produces higher zone targets because it accounts for the fact that fit people start with a lower resting HR and have more dynamic range to work with.

Recovery (50-60%) is genuinely conversational - you could sing. It is for active recovery, warm-ups and cool-downs. Fat Burn (60-70%) is the longest part of any aerobic build; it is where most of your weekly volume should sit if you are building base fitness. Aerobic (70-80%) is comfortably hard, the tempo zone, where threshold improves. Anaerobic (80-90%) is what most people picture when they say 'hard cardio' - intervals of 3 to 8 minutes. VO2 Max (90-100%) is short, awful efforts of 30 seconds to 5 minutes that improve maximum oxygen uptake.

The single most common mistake is spending all your time in zone 3 (aerobic). Comfortable enough to do every day, hard enough to feel like training, hard enough to leave you tired without any of the adaptations of true zone 2 or true zone 5. The 80/20 rule from coaching research: 80% of weekly minutes in Recovery and Fat Burn, 20% in Aerobic and above. If a session feels moderately hard the whole way, you are probably grey-zoning. Use a chest strap and push the easy days easier.

The 220-minus-age formula was derived in the 1970s and has a standard deviation of about 10-12 bpm. So for any given age, real max HR ranges over roughly 25 bpm. A 40-year-old might have a true max of 168 or 192. The calculator's estimate is the population midpoint, not your actual ceiling. If your zone 4 efforts feel impossibly easy or impossibly hard at the predicted heart rates, your true max HR is probably above or below the formula.

The accurate way to find max HR is a hard test. After a thorough warm-up, do 4 minutes hard, 2 minutes easy, then run or cycle uphill for 3 minutes increasing pace until you cannot maintain it. The peak number on your watch is close to true max HR. Do not do this without a baseline of training, and not at all if you have any history of heart issues. Beta blockers, thyroid medication and some antidepressants change resting and max HR; if you take any, ask your GP before training to numbers from this calculator.

If you know your resting heart rate, Karvonen is the better default. Resting HR drops as you get fitter, so the gap between the two methods grows over a training year. A new runner with a resting HR of 75 and an experienced runner with a resting HR of 50 will have very different zones at the same age, and Karvonen reflects that. The plain 220-age method ignores resting HR completely.

Measure resting HR for accuracy. First thing in the morning, before getting up, before coffee or your phone alarm, take a 30-second pulse at the wrist or neck and double it. Do that for three to seven days and average. A typical adult sits at 60-80 bpm; trained endurance athletes are often in the 40s; under 40 bpm is normal in highly trained runners and cyclists but warrants a chat with your GP if you also feel dizzy or fatigued. The [TDEE calculator](/tdee-calculator) is useful alongside this if you are training for fat loss and want to set the calorie target to match the cardio volume.