What is the Karvonen formula?

The Karvonen method calculates target heart rate zones using heart rate reserve (HRR = max HR − resting HR): Target HR = (HRR × intensity%) + resting HR. It is more personalised than the simple percentage method because it accounts for your fitness level (reflected in resting HR).

How accurate is 220 minus age?

The formula 220 − age is an average estimate with a standard deviation of approximately ±10–12 bpm. Some individuals' true maxHR may differ significantly. For more accuracy, perform a graded exercise test under medical supervision.

Which formula should I use?

Karvonen is generally preferred for personalised training plans because it accounts for individual fitness. The simple formula is fine for general guidance or if you do not know your resting heart rate.

What is Zone 2 training?

Zone 2 (60–70% of max HR or equivalent Karvonen) is associated with improved mitochondrial density, fat oxidation, and aerobic base. Many endurance athletes and health experts recommend spending the majority of training time in Zone 2.

Target Heart Rate Zones — Karvonen Method

Understanding your heart rate zones is essential for effective training. This calculator uses either the scientifically-supported Karvonen method (Heart Rate Reserve) or the simpler percentage-of-max method to calculate five training zones personalised to your age and fitness level.

How Maximum Heart Rate Is Estimated

The formula 220 − age is the most widely used estimator of maximum heart rate (HRmax). It was derived from a 1971 paper by Fox et al. based on a literature review (not original research). Its simplicity made it ubiquitous, but it has a standard deviation of approximately ±10–12 bpm — meaning your true HRmax could be significantly higher or lower.

More accurate formulas have been proposed (e.g., Tanaka: HRmax = 208 − 0.7 × age), but 220 − age remains the standard for practical use and is what this calculator uses.

The Karvonen Method

Developed by Finnish physiologist Martti Karvonen in 1957, the Karvonen formula introduces Heart Rate Reserve (HRR):

HRR = Max HR − Resting HR

Target HR for a given intensity = (HRR × intensity%) + Resting HR

The key insight is that resting heart rate reflects cardiovascular fitness. A well-trained endurance athlete may have a resting HR of 40–50 bpm, while a sedentary adult typically sits at 70–80 bpm. By incorporating resting HR, the Karvonen formula produces training zones that better reflect individual physiology.

The Five Training Zones

Zone	Intensity	Perceived Effort	Primary Benefit
Zone 1 (Recovery)	50–60%	Very easy, can sing	Active recovery, blood flow
Zone 2 (Base Aerobic)	60–70%	Conversational	Fat oxidation, aerobic base
Zone 3 (Aerobic)	70–80%	Moderately hard, limited talking	Aerobic fitness, VO2 improvement
Zone 4 (Threshold)	80–90%	Hard, difficult to speak	Lactate threshold, speed
Zone 5 (Maximum)	90–100%	All-out, unsustainable	Peak power, race simulation

Zone 2 — The Foundation Zone

Zone 2 training has received considerable attention in sports science and longevity research. Training at this intensity:

Increases mitochondrial density — more and larger mitochondria in muscle cells
Enhances fat oxidation — improves the body’s ability to use fat as fuel
Builds aerobic base without excessive stress on the body
Improves cardiac output — the heart becomes more efficient at pumping blood
Promotes recovery between high-intensity sessions

Many elite endurance athletes spend 70–80% of their total training volume in Zone 2.

Zone 4 — Lactate Threshold Training

Zone 4 (80–90%) targets the lactate threshold — the exercise intensity above which lactate accumulates faster than it can be cleared. Training in this zone:

Raises the lactate threshold, allowing you to sustain higher intensities longer
Is essential for improving race performance at distances from 5K to marathon
Should constitute approximately 10–15% of weekly training volume

Measuring Your True Resting Heart Rate

For the Karvonen formula to work well, you need an accurate resting heart rate (RHR):

Measure on a rest day, first thing in the morning before getting out of bed
Use a chest strap heart rate monitor or count for 60 seconds at the radial pulse (wrist)
Take readings on 3–5 consecutive mornings and average them
A lower resting HR (typically 40–60 bpm in trained athletes) indicates better cardiovascular fitness

Practical Training Application

Beginner (less than 6 months of training):

Focus on Zone 1–2 (80% of sessions)
Short Zone 3 sessions (20%)
Avoid Zones 4–5 until a base is established

Intermediate (6–24 months):

Zone 2 dominant (70%)
Zone 3–4 intervals (20%)
Zone 5 sprints once per week (10%)

Advanced (2+ years):

Periodised with higher Zone 4–5 work in race-specific phases
Zone 2 maintained year-round as aerobic base

Frequently Asked Questions

Why does the Karvonen formula give different zones than the simple method? Because it accounts for resting heart rate. A fit person with an RHR of 45 bpm has a much larger heart rate reserve than an unfit person with an RHR of 85 bpm, even at the same age. Karvonen zones reflect this difference; simple percentage zones do not.

Can I wear a smartwatch to track heart rate zones? Yes, but accuracy varies. Wrist-based optical sensors perform well during steady-state cardio but can be unreliable during high-intensity intervals or activities with significant wrist movement. A chest strap HR monitor remains the most accurate consumer option.

What if my heart rate stays too high in Zone 2? This is common in beginners. You may need to slow down significantly — possibly to a walk — to stay in Zone 2. With consistent training, your pace at any given heart rate will improve substantially over 3–6 months.