What Is Heart Rate Reserve? How to Calculate It for Training Zones

Quick answer: Heart rate reserve (HRR) is the difference between your maximum heart rate and resting heart rate. It helps estimate exercise intensity by accounting for both how fast your heart can beat during hard exercise and how fast it beats at rest. You can use the Karvonen formula to turn a percentage of heart rate reserve into a target training heart rate.

Heart Rate Reserve = Maximum Heart Rate − Resting Heart Rate

Target Heart Rate = Resting Heart Rate + (Heart Rate Reserve × Target Intensity)

For example, a 35-year-old with an estimated maximum heart rate of 185 BPM and a resting heart rate of 65 BPM has an HRR of 120 BPM. At 70% HRR, the target exercise heart rate is 149 BPM.

HRR-based training can be useful for organizing workout intensity, but the results are estimates. Age-predicted maximum heart rate, sensor accuracy, medications, fitness level, and individual physiology can all affect your actual training zones.

What Is Heart Rate Reserve?

Heart rate reserve describes the difference between your resting heart rate (RHR) and maximum heart rate (HRmax).

Think of these values as two reference points:

• Resting Heart Rate (RHR): How many times your heart beats per minute while you are physically at rest.
• Maximum Heart Rate (HRmax): The highest heart rate you can reach during sufficiently intense exercise.
• Heart Rate Reserve (HRR): The difference between those two numbers.

The formula is:

HRR = HRmax − RHR

If your maximum heart rate is 185 BPM and your resting heart rate is 65 BPM:

185 − 65 = 120 BPM

Your estimated heart rate reserve is 120 BPM.

This does not mean your heart has a fixed number of "extra beats" available or that HRR directly measures your aerobic capacity.

It is a mathematical range that can help you estimate exercise intensity relative to your own resting and maximum heart-rate values.

Why use heart rate reserve instead of maximum heart rate alone?

Two people of the same age can have similar estimated maximum heart rates but different resting heart rates.

For example:

Although both people have the same estimated maximum heart rate, their target heart rates at 70% HRR are different.

That is the main advantage of the heart rate reserve method: it incorporates an individual resting measurement rather than relying exclusively on maximum heart rate.

However, a more personalized calculation is still not the same as measuring your true physiological training thresholds in a laboratory.

How to Calculate Heart Rate Reserve Using the Karvonen Formula

The Karvonen method calculates target exercise heart rate from three inputs:

1. Maximum heart rate;
2. Resting heart rate; and
3. Desired exercise intensity expressed as a percentage of HRR.

Step 1: Estimate your maximum heart rate

One common age-based formula is:

Estimated HRmax = 220 − Age

For someone aged 35:

220 − 35 = 185 BPM

Estimated maximum heart rate: 185 BPM.

This formula is simple, but it is not precise for every person.

Another commonly used population-based estimate is:

Estimated HRmax = 208 − (0.7 × Age)

Both approaches provide estimates. A person's actual maximum heart rate can differ meaningfully from either prediction.

If you need precise training zones, an appropriately supervised exercise test or individualized physiological assessment may be more useful.

Do not attempt an unsupervised maximal-effort test simply to obtain a number, particularly if you have a cardiovascular condition or are unfamiliar with high-intensity exercise.

Step 2: Find your resting heart rate

Resting heart rate is most useful when measured under consistent conditions.

A practical approach is to measure it in the morning, before exercise, caffeine, or significant daily activity.

You can check your pulse manually:

1. Sit or lie quietly in a comfortable position.
2. Place two fingertips over the artery on the thumb side of your wrist.
3. Count the beats for 30 seconds.
4. Multiply by two to estimate beats per minute.

For example:

32.5 beats in 30 seconds would correspond to approximately 65 BPM.

In practice, counting for a full minute can make manual measurement easier to interpret without estimating a partial beat.

A wearable may also provide resting-heart-rate information, but check how it defines that value.

A morning resting measurement, a sleeping heart-rate average, and a random seated reading are not necessarily interchangeable.

For training calculations, choose a consistently measured resting value rather than whichever reading happens to be lowest.

Step 3: Subtract resting heart rate from maximum heart rate

Continue with the same example:

• Age: 35 years
• Estimated HRmax: 185 BPM
• Resting HR: 65 BPM

HRR = 185 − 65 = 120 BPM

The estimated heart rate reserve is 120 BPM.

Step 4: Apply the Karvonen formula

To calculate a target training heart rate:

Target HR = Resting HR + (HRR × Intensity)

Convert the intensity percentage into a decimal.

For example:

• 60% becomes 0.60;
• 70% becomes 0.70;
• 80% becomes 0.80.

For 70% HRR:

Target HR = 65 + (120 × 0.70)

Target HR = 65 + 84

Target HR = 149 BPM

For a target range, repeat the calculation using the lower and upper intensity percentages.

Important: Do not forget to add resting heart rate back into the final calculation. Multiplying HRR by a percentage gives only the selected fraction of your reserve, not your complete target heart rate.

Worked Example: Five Heart Rate Reserve Training Zones

Once you know your HRR, you can calculate target heart-rate ranges for different exercise intensities.

The following example uses:

• Age: 35 years;
• Estimated maximum heart rate: 185 BPM;
• Resting heart rate: 65 BPM; and
• Heart rate reserve: 120 BPM.

To demonstrate the calculation, we divide the upper portion of HRR into five consecutive bands.

These are illustrative training-zone labels, not universal clinical or physiological thresholds. Different coaches, exercise programs, and wearable platforms use different zone boundaries.

Values are rounded to whole BPM. Each row starts at the specified lower percentage and ends just below the next zone's boundary, except the final row.

How do you calculate a training-zone range?

Suppose you want the example range from 60% to 70% HRR.

First calculate the lower boundary:

65 + (120 × 0.60) = 137 BPM

Then calculate the upper boundary:

65 + (120 × 0.70) = 149 BPM

The calculated boundaries are 137 and 149 BPM.

In the example table, Zone 2 includes values from approximately 137 BPM up to, but not including, the 149 BPM boundary. That boundary begins Zone 3.

You can apply the same method to any other percentage range.

How do these zones relate to moderate and vigorous exercise?

General exercise-intensity classifications often use approximately:

• 40%–59% HRR: Moderate-intensity exercise;
• 60%–89% HRR: Vigorous-intensity exercise.

These are general intensity categories, not the same thing as a particular five-zone training system.

For the example person:

• 40% HRR corresponds to 113 BPM;
• 59% HRR corresponds to approximately 136 BPM;
• 60% HRR corresponds to 137 BPM; and
• 89% HRR corresponds to approximately 172 BPM.

Actual exercise intensity depends on individual fitness, physiology, and how the effort feels.

Do not assume that a zone called "Zone 2" on one device necessarily represents the same intensity as Zone 2 on another device.

For a broader introduction to workout intensity, read our guide to heart rate zones for everyday fitness.

Heart Rate Reserve vs. Maximum Heart Rate, HRV, and Heart Rate Recovery

Several heart-related measurements have similar names but describe different things.

Understanding these distinctions helps prevent incorrect training calculations and misleading comparisons.

HRR vs. percentage of maximum heart rate

There are two common ways to estimate an exercise target:

Maximum-heart-rate method:

Target HR = HRmax × Intensity

Heart-rate-reserve method:

Target HR = RHR + [(HRmax − RHR) × Intensity]

They are not mathematically equivalent.

Using our example person:

The difference is approximately 19 BPM.

That is why it matters whether an exercise plan uses %HRmax or %HRR.

Do not take a percentage designed for one system and apply it to the other.

Heart rate reserve vs. heart rate variability (HRV)

Heart Rate Variability (HRV) measures variation in the time intervals between consecutive heartbeats.

Heart Rate Reserve (HRR) measures the difference between maximum and resting heart rate.

HRV is typically expressed in milliseconds, while HRR is expressed in beats per minute.

These measurements cannot replace one another.

For more detail, see our guide to HRV vs. resting heart rate.

Does HRR also mean heart rate recovery?

Yes. The abbreviation HRR is also commonly used for Heart Rate Recovery.

Heart rate recovery describes how much heart rate decreases after exercise ends, usually over a defined recovery interval.

Heart rate reserve and heart rate recovery are different measurements, even though both may be abbreviated HRR.

When reading research, workout summaries, or wearable data, check which definition is being used.

How to Use Heart Rate Reserve Zones in Real Workouts

HRR calculations are useful when they help you pace exercise more appropriately.

The goal is not to stay within a precise BPM range every second.

It is to understand how your cardiovascular response changes with exercise intensity.

Easy and steady aerobic training

For walking, jogging, cycling, or steady aerobic training, a target heart-rate range may help you avoid starting too hard.

However, your actual aerobic training intensity depends on individual physiological thresholds.

A generic HRR zone does not guarantee that you are below your first ventilatory or lactate threshold.

Use a combination of:

• Heart Rate;
• breathing comfort;
• the Talk Test;
• Rate of Perceived Exertion (RPE); and
• your ability to sustain the activity.

During moderate effort, you can typically talk but may find singing difficult.

During vigorous effort, speaking more than a few words without pausing becomes harder.

For a more detailed discussion of aerobic training intensity, see Zone 2 vs. Zone 3 heart rate.

Harder workouts and intervals

HRR-based ranges can also help structure more demanding workouts.

For example, a training plan may include:

• a lower-intensity warm-up;
• a steady aerobic segment;
• several harder intervals; and
• a gradual cooldown.

However, Heart Rate does not respond instantaneously to changes in exercise intensity.

During a short sprint, mechanical power and effort may rise much faster than the measured heart rate.

That makes heart-rate targets less useful for extremely short intervals than for longer, steadier efforts.

For short, intense work, pace, power, duration, and perceived effort can be more informative than trying to force the heart into a particular zone before the interval ends.

Use the target as a guide rather than a strict rule

A calculated HRR target can make training more structured, but it is not a personalized medical safety limit.

Do not increase exercise intensity merely because the device says you have not reached the target.

If the workout already feels unusually difficult, review your breathing, fatigue, heat exposure, hydration, and overall condition.

Training quality depends on more than reaching one calculated number.

Why Heart Rate Reserve Calculations Can Be Inaccurate

The Karvonen formula is mathematically straightforward, but its usefulness depends on the accuracy and appropriateness of the inputs.

Maximum heart rate may be estimated incorrectly

The familiar 220-minus-age formula is a population-level estimate.

It cannot reliably predict every individual's maximum heart rate.

Two people of the same age may have meaningfully different HRmax values.

A calculation based on an inaccurate HRmax can shift every estimated training-zone boundary.

Where precise exercise prescription matters, professionally supervised testing may be appropriate.

Resting heart rate changes with circumstances

Resting Heart Rate can vary with:

• sleep;
• stress;
• dehydration;
• illness;
• temperature;
• medications;
• recent exercise; and
• measurement timing.

Using one unusually high or low resting reading can affect your calculated training zones.

For a more stable estimate, compare measurements obtained under consistent resting conditions across several days.

Do not substitute the lowest heart-rate reading recorded during sleep for an awake resting measurement without considering the difference between those conditions.

Medication and medical conditions can change the relationship

Some medications, including beta blockers, can lower exercise heart-rate responses.

Other medications and medical conditions may also affect heart rate.

If you have a known cardiovascular condition, take medication that changes heart rate, or are participating in cardiac rehabilitation, ask your healthcare professional how your exercise intensity should be prescribed.

Generic age-based formulas may be unsuitable for your situation.

Stop exercising and seek appropriate medical assistance if you experience chest pain, fainting, significant dizziness, unusual breathlessness, or other concerning symptoms.

Wearable heart-rate data also has limitations

Most consumer smartwatches and smart rings use optical sensing to estimate Heart Rate.

Movement, sensor position, poor skin contact, and changing measurement conditions can affect accuracy.

In addition, not every wearable uses HRR when generating its workout zones.

Some use percentages of estimated maximum heart rate. Others use proprietary methods or allow personal settings.

Before comparing your Karvonen calculation with a wearable's zone display, check which formula and inputs the device actually uses.

How RingConn Can Support Heart Rate and Recovery Awareness

HRR-based training is primarily about estimating exercise intensity.

Wearables can provide useful context by helping you observe Heart Rate, resting patterns, activity, sleep, and other supported wellness measurements over time.

A fitness ring can support passive day-and-night tracking without requiring another large screen on the wrist.

For example, the RingConn Gen 3 health tracking ring uses optical sensing to estimate Heart Rate in beats per minute and provides supported information including HRV, Sleep, Activity, and Stress trends.

These measurements can help provide context for questions such as:

• Is my resting Heart Rate changing over several weeks?
• How did my Heart Rate respond to a recent workout?
• Did harder training coincide with different sleep or recovery-related trends?
• Does today's exercise feel unusually difficult compared with my normal routine?

However, recording Heart Rate and displaying workout-related information does not necessarily mean a device automatically calculates Karvonen zones.

If you want to use a particular HRR-based training system, confirm whether your training platform supports it and whether your maximum and resting heart-rate inputs can be adjusted.

RingConn wellness data should be used for personal trend awareness rather than a substitute for laboratory exercise testing or a clinically prescribed exercise plan.

Final takeaway: Heart Rate Reserve is the difference between maximum and resting Heart Rate. The Karvonen formula uses that difference to estimate target BPM values for exercise.

HRR = HRmax − RHR

Target HR = RHR + (HRR × Intensity)

For a 35-year-old with an estimated maximum Heart Rate of 185 BPM and resting Heart Rate of 65 BPM, HRR is 120 BPM and the 70% HRR target is 149 BPM.

Use the result as a training reference, then consider perceived effort, individual physiology, recovery, and the limits of heart-rate measurements.

Frequently Asked Questions

What is heart rate reserve in simple terms?

Heart Rate Reserve is the difference between your maximum Heart Rate and Resting Heart Rate. For example, if your maximum Heart Rate is 185 BPM and your resting Heart Rate is 65 BPM, your HRR is 120 BPM. This number can be used to estimate training targets through the Karvonen formula.

How do you calculate heart rate reserve?

Subtract your Resting Heart Rate from your maximum Heart Rate. The formula is HRR = HRmax − RHR. You can then calculate a target training heart rate by multiplying HRR by your desired intensity fraction and adding your resting Heart Rate back to the result.

What is the Karvonen formula for target heart rate?

The Karvonen formula is Target HR = Resting HR + [(Maximum HR − Resting HR) × Intensity]. If your resting Heart Rate is 65 BPM, maximum Heart Rate is 185 BPM, and desired intensity is 70% HRR, your target is 65 + (120 × 0.70) = 149 BPM.

What is a good heart rate reserve?

There is no single ideal HRR value for everyone. HRR depends on maximum and resting Heart Rate, which vary with age, fitness, genetics, medication, and medical conditions. A higher calculated HRR does not automatically prove better health or fitness. Interpret it alongside your circumstances and other fitness information.

Is 70% heart rate reserve the same as 70% maximum heart rate?

No. A percentage of HRR includes resting Heart Rate in the calculation, while a percentage of maximum Heart Rate does not. For a person with an HRmax of 185 BPM and RHR of 65 BPM, 70% HRmax is approximately 130 BPM, while 70% HRR is 149 BPM.

Is heart rate reserve the same as HRV?

No. Heart Rate Reserve describes the difference between maximum and resting Heart Rate and is used in exercise-intensity calculations. Heart Rate Variability describes variation in the intervals between heartbeats and can provide stress and recovery context. HRR is expressed in BPM; HRV is commonly expressed in milliseconds.

Can a smartwatch or smart ring calculate heart rate reserve automatically?

Some wearable platforms may support HRR-based training zones, while others use percentages of maximum Heart Rate or different calculation methods. A device that measures Heart Rate does not automatically provide Karvonen zone calculations. Check the platform's zone settings, maximum-heart-rate estimate, and resting-heart-rate definition before relying on its displayed ranges.

Medical disclaimer: This article is for general fitness education and is not a personalized exercise prescription. RingConn products are intended for personal health and wellness awareness and are not medical devices. Consumer Heart Rate, HRV, Sleep, Activity, Stress, and other wellness metrics should not replace medical assessment or professionally prescribed training limits. Consult a healthcare professional before using high-intensity exercise targets if you have cardiovascular disease, take heart-rate-altering medication, or have other relevant medical concerns. Seek prompt medical care for concerning symptoms during exercise.