How this works
The tool estimates your maximum heart rate with the formula 208 minus 0.7 times your age, then splits it into five zones by percentage. Real maximum heart rates vary by about 10 beats per minute in either direction, so treat the numbers as a guide.
Most beginners get the biggest benefit from time in the easier zones, where you can still talk in full sentences. Harder zones are best used in short intervals.
Talk to your doctor before starting vigorous exercise if you have a heart condition, high blood pressure or other health concerns, or if you take medication that affects heart rate. Stop and get help if you have chest pain, severe breathlessness or dizziness.