Why train by heart rate
Your heart rate is a live gauge of how hard your body is working. Training in the right zone keeps easy days easy and hard days hard, which is how fitness improves without overdoing it. The zones are shares of your maximum heart rate, commonly estimated as 220 minus your age.
The zones this tool shows
The fat-burn or moderate zone sits around 50–70% of maximum — a comfortable, conversational effort you can hold for a long time. The cardio or aerobic zone is roughly 70–85%, harder breathing that builds endurance and heart strength. Above that lies the peak zone, used only in short bursts.
A more personal estimate
If you enter your resting heart rate, the tool switches to the Karvonen method, which bases the zones on your heart-rate reserve — the gap between resting and maximum. This personalises the numbers to your fitness, and is generally more accurate than percentages of maximum alone.
Note: these are general estimates for healthy adults, not medical advice. Check with a doctor before starting intense exercise if you have any health concerns.
Frequently asked questions
Is the fat-burn zone the best for losing weight?
It burns a higher share of fat per calorie, but higher-intensity work burns more total calories. Both help; the best zone is the one you'll do consistently.
Is 220 minus age accurate?
It's a widely used estimate but can be off by 10–12 bpm for an individual. A lab test or a chest-strap monitor over time gives a more personal maximum.