Target heart rate calculator

What is a target heart rate calculator?

A target heart rate calculator is a free online tool that estimates the heart rate range you should aim for during exercise to train at a chosen intensity. Instead of relying on a single number, it gives you a lower and an upper bound so you can keep your effort inside a sensible window. The calculation uses the Karvonen formula, also known as the heart-rate reserve method, which is widely regarded as more personalised than a plain percentage of maximum heart rate because it factors in your resting heart rate.

Why the heart-rate reserve method?

Many simple charts compute a target zone as a flat percentage of your maximum heart rate. That approach ignores how fit you already are. The Karvonen method instead works from your heart-rate reserve, the difference between your maximum heart rate and your resting heart rate. Because a lower resting heart rate usually signals better cardiovascular fitness, two people of the same age can end up with different target zones, which more closely reflects the effort each one is actually putting in.

How to use the calculator

1. Enter your age in years. This is used to estimate your maximum heart rate.
2. Enter your resting heart rate in beats per minute. Measure it when you are calm, ideally first thing in the morning before getting out of bed.
3. Set the lower and upper intensity percentages that define your zone. The defaults of 50% and 85% cover a broad, general-fitness training band.

The calculator then reports your maximum heart rate and the lower and upper edges of your target zone in beats per minute.

Formula

Your maximum heart rate is estimated with the common age-based formula:

$\text{HR}_{max} = 220 - \text{age}$

The target heart rate at a given intensity is then found with the Karvonen formula:

$\text{HR}_{target} = (\text{HR}_{max} - \text{HR}_{rest}) \times \text{intensity} + \text{HR}_{rest}$

where:

• HR_max is the maximum heart rate,
• HR_rest is the resting heart rate,
• intensity is the chosen fraction of the heart-rate reserve (e.g. 0.5 for 50%).

The term in parentheses, HR_max minus HR_rest, is the heart-rate reserve. Multiplying it by the intensity and adding the resting heart rate back yields the target beats per minute.

Worked examples

1. A 30-year-old with a resting heart rate of 60 bpm, training at 50% to 85%.

   $\text{HR}_{max} = 220 - 30 = 190 \text{ bpm}$

   The heart-rate reserve is 190 − 60 = 130 bpm.

   $\text{lower} = 130 \times 0.50 + 60 = 125 \text{ bpm}$

   $\text{upper} = 130 \times 0.85 + 60 = 170.5 \text{ bpm}$

   So the target zone runs from about 125 to 171 bpm.

2. A 40-year-old with a resting heart rate of 70 bpm, training at 60% to 80%.

   $\text{HR}_{max} = 220 - 40 = 180 \text{ bpm}$

   The heart-rate reserve is 180 − 70 = 110 bpm.

   $\text{lower} = 110 \times 0.60 + 70 = 136 \text{ bpm}$

   $\text{upper} = 110 \times 0.80 + 70 = 158 \text{ bpm}$

   The target zone for this session runs from 136 to 158 bpm.

Notes

These formulas produce estimates only. The 220 − age rule for maximum heart rate is a population average and can be off by a fair margin for any individual. Your true maximum heart rate, your medications, and your health conditions can all shift the right zone for you. Treat the results as a starting point and consult a doctor or qualified trainer before beginning a new programme, especially if you have any cardiovascular concerns.

FAQs

What is heart-rate reserve?

Heart-rate reserve is the gap between your maximum heart rate and your resting heart rate. It represents how much your heart rate can rise from rest to maximum effort, and it is the basis of the Karvonen calculation.

Why does resting heart rate matter for the zone?

Because the Karvonen method scales intensity against your heart-rate reserve, a lower resting heart rate widens that reserve and shifts your target zone. This makes the result more specific to your fitness than a plain percentage of maximum heart rate.

What intensity should I choose?

A broad 50% to 85% band suits general fitness. Lower percentages (around 50% to 60%) favour easy, recovery-style effort, while higher percentages (around 70% to 85%) build cardiovascular endurance. Pick the range that matches your goal for the session.

How do I measure my resting heart rate?

Sit or lie still, find your pulse at the wrist or neck, and count the beats for 60 seconds. The most reliable reading is taken in the morning before you get out of bed.

Is the 220 − age formula accurate?

It is a convenient average, not a precise measurement. Individual maximum heart rates vary widely, so consider a supervised test if you need an exact figure for serious training.