Cardio tool

Heart Rate and Zone 2 Calculator

Use the Karvonen method when resting heart rate is known, or an age-based estimate when it is not.

Use the toolFree · No account required

Enter heart-rate details

If you know your resting heart rate, we use the more individualized Karvonen method.

The calculation runs on your device; your health inputs are not sent or stored.

Estimated heart-rate zones

Enter your age to estimate your zones.

Zone 2 definitions vary by method. The 220−age equation is an average. Consult a healthcare professional if you have a heart condition or take heart-rate-altering medication.

Review your heart-rate estimate

Review the calculation methods and limitations below, or explore trainers for your training plans.

Quick guide

See the Zone 2 method with the number

The age-based method builds percentage ranges from an estimated maximum heart rate. When resting heart rate is entered, the Karvonen method also uses heart-rate reserve, so the results do not have to match.

How to use it

  1. 1Enter your age; optionally use an average of calm resting readings.
  2. 2Check which method was used in the result.
  3. 3Interpret the number alongside talk comfort and perceived effort.

How should you read it?

Without a resting heart rate, the tool shows only an age-based estimate. If your watch and breathing feel disagree, forcing the number is less useful than reducing intensity and observing the response.

Keep the limits in view

Medication, rhythm conditions, device error, and individual variation can change the result. Seek professional guidance for a heart condition or related concern.

What this tool cannot do

Age-predicted maximum heart rate is an average. Zone 2 definitions can vary by method and device.

AHA target heart-rate guidance

Sources last checked: September 2026