Zone 2 heart rate calculator

How your zone 2 range is calculated

Zone 2 is defined as 60 to 70 percent of heart rate reserve, or 60 to 70 percent of max heart rate if you prefer the simpler method. The calculator estimates your max heart rate with the Tanaka formula (208 minus 0.7 times your age), then applies whichever method you pick.

Worked example (Karvonen)

Age 40, resting heart rate 60 bpm: max heart rate is 208 − 0.7 × 40 = 180 bpm. Heart rate reserve is 180 − 60 = 120 bpm. Zone 2 lower bound: 60 + 0.60 × 120 = 132 bpm. Upper bound: 60 + 0.70 × 120 = 144 bpm. Zone 2 for this person is 132 to 144 bpm.

Worked example (percent of max)

Same 180 bpm max heart rate, no resting heart rate needed: lower bound 0.60 × 180 = 108 bpm, upper bound 0.70 × 180 = 126 bpm. Zone 2 by this method is 108 to 126 bpm, noticeably lower than the Karvonen range for the same person, which is why the method you pick matters.

Heart rate reserve versus percent of max: which to use

The two methods do not agree because percent of max ignores your resting heart rate entirely, while Karvonen builds it in as a rough marker of fitness. Karvonen sits above percent of max because the resting heart rate is added as a floor under every boundary, so the uplift over percent of max grows with a higher resting heart rate and shrinks for a fitter person with a low one, the opposite of what a wider reserve alone might suggest.

If you have a reliable resting heart rate, taken first thing in the morning over a few days, Karvonen is the more individualised and generally preferred method. If you do not, the 60 to 70 percent of max shortcut is a reasonable stand in, and it is the same band the heart rate zone calculator publishes for zone 2 in its five-zone table, so the two tools agree whichever one a reader lands on first.

Zone 2 at a glance

Same person, two methods. Karvonen tends to land roughly 18 to 24 bpm higher than percent of max for the same effort, more at the bottom of the range than the top.

What zone 2 training actually does

At this intensity, effort is easy enough that the body relies mostly on fat and oxygen rather than fast, limited carbohydrate stores, which is what makes long, frequent sessions here sustainable without piling up fatigue. Training consistently in this range drives adaptations that harder efforts cannot reach as efficiently.

Mitochondrial density

Repeated low intensity effort is one of the strongest known stimuli for building more, and more efficient, mitochondria in muscle cells, the structures that convert fat and oxygen into usable energy. Sports physiologist Iñigo San-Millán, who has worked with elite endurance athletes and popularised zone 2's role in mitochondrial health, has published research linking time spent at this intensity to improved metabolic flexibility, the ability to switch efficiently between burning fat and carbohydrate as effort changes.

A bigger aerobic base without the recovery cost

Because the effort is low, the body recovers from a zone 2 session in hours rather than days, which means it can be repeated far more often than threshold or interval work. That frequency is what builds capillary density, stroke volume and general aerobic capacity over months, the base that harder training later sits on top of.

How long a zone 2 session should be

Zone 2 rewards duration more than intensity, so sessions are typically longer than a standard workout: 30 to 90 minutes is the usual range, with more experienced endurance athletes sometimes going longer still. Shorter than 30 minutes and there is not much time for the aerobic system to be the dominant fuel source; there is no real upper limit beyond what recovery and time allow.

Frequency matters as much as length. Three to five sessions a week is a common target for someone building an aerobic base, since the low fatigue cost is exactly what allows that frequency without interfering with harder training days.

Building up gradually

If 30 to 90 minutes sounds like a lot more than your current cardio routine, start at the lower end and add five to ten minutes every week or two rather than jumping straight to 90 minutes in one session. The intensity is easy, but the joints, tendons and connective tissue still need time to adapt to the added volume, even if the heart and lungs cope with it immediately.

How to use your zone 2 range

Treat the range as a ceiling to stay under, not a number to sit exactly on. If you find yourself drifting above the top of the range to hold a pace, that pace is not a zone 2 session that day, whatever it felt like when you started.

The talk test as a backup

If a heart rate monitor is not available, a reasonable proxy is holding a full conversation without gasping for breath. It is not as precise as a measured range, but it catches the same mistake heart rate does: creeping into zone 3 without noticing.

Fitting it around other training

For most people zone 2 is not the only training in a week, it sits alongside strength work and some harder cardio. A common structure is putting zone 2 on the days between hard sessions, so it adds aerobic volume without adding to the fatigue that harder efforts need recovery from.

Pace or power versus heart rate: why they drift apart

Heart rate is not the only way to gauge zone 2 effort. Runners often use pace, cyclists often use power, and both are more instantly responsive than heart rate, which lags behind actual effort by tens of seconds. But over a longer session the two measures can quietly pull apart, and it is worth understanding why before trusting one over the other.

Cardiac drift

Hold the exact same pace or power output for 60 to 90 minutes, especially somewhere warm, and heart rate tends to creep upward even though the external output has not changed. This is cardiac drift: as the session goes on, the body loses fluid to sweat, blood volume drops slightly, and the heart has to beat faster to move the same amount of blood and keep pace with rising core temperature. A session that started at 130 bpm holding a given pace can finish at 140 bpm or higher at that identical pace, with nothing about the effort itself having changed.

Which one should you trust

For a genuinely easy, aerobic session, heart rate is usually the better governor precisely because it reflects what the cardiovascular system is actually doing right now, drift and all. Pace or power tells you what you are producing, not what it is costing your heart to produce it, and on a hot day or a poorly slept night that cost can be considerably higher for the same output. If your heart rate is climbing out of zone 2 even though your pace has not changed, the honest response is to slow down, not to distrust the heart rate reading.

Using both together

Over months of consistent zone 2 training, a useful trend to track is the pace or power you can hold at a fixed heart rate, sometimes called aerobic decoupling or efficiency. As fitness improves, the same heart rate should let you hold a slightly faster pace or higher power with less drift over the course of a session, which is a more meaningful fitness signal than either number in isolation.

Running zone 2 on a bike, rower and treadmill

The bpm range itself does not change with the activity, since it is calculated from age and resting heart rate, not from what you are doing. What changes is how easy it is to actually hit and hold that range on each piece of equipment.

Cycling

Outdoor cycling makes zone 2 harder to hold steady than an indoor trainer, since terrain, wind and traffic stops constantly push effort above and below the target. An indoor smart trainer paired with a power meter is the most controlled way to hold zone 2 on a bike: pick a power target that keeps heart rate in range, then let power be the steering input while heart rate confirms the effort is landing where it should. On an outdoor ride, err towards the lower half of the zone on climbs and let it drift towards the top on flat sections rather than chasing an exact number the whole way.

Rowing

Rowing tempts a higher stroke rate than zone 2 calls for, since a strong, satisfying pull at a high stroke rate feels more like "real" training than the lower, more patient rate that usually keeps heart rate in range for most rowers. Lower the stroke rate before lowering the power per stroke; a longer, more patient stroke at a lower rate holds pace more efficiently at low heart rates than a rushed, shorter one.

Treadmill

A treadmill removes wind and terrain, which makes it one of the easier places to hold a steady zone 2 heart rate once the right speed and incline are dialled in. The catch is incline: even a modest grade raises heart rate noticeably at the same speed, so a pace that sits in zone 2 flat can push into zone 3 with a hill setting on. Adjust speed downward as incline goes up if the goal is staying in zone 2, rather than holding the same pace and letting heart rate rise.

Swimming

Heart rate tends to read several beats lower in the pool for the same perceived effort, since the horizontal body position and water pressure both assist blood return to the heart, similar to the effect that lowers measured max heart rate in swimmers. A poolside heart rate check right after stopping, since most watches cannot read heart rate accurately underwater, will usually undershoot a true zone 2 effort if you compare it directly to a land-based number without adjusting expectations.

Getting an accurate resting heart rate for Karvonen

The Karvonen method is only as good as the resting heart rate you feed it. Since it sets the floor that every percentage in the calculation is added to, an error here shifts the entire zone 2 range, not just one end of it.

The classic method

Take your pulse first thing in the morning, before getting out of bed, sitting up, checking your phone or having coffee. Count beats for a full 60 seconds rather than 15 seconds multiplied by four, since a short count amplifies any counting error. Repeat this over three or four consecutive mornings and average the results rather than trusting a single reading, which can be skewed by a restless night, a late meal or simple counting mistakes.

Using a wearable instead

Most fitness watches and rings track resting heart rate automatically overnight and will show a trend over days or weeks in their app, which is generally more reliable than a single manual reading since it averages many hours of true rest rather than one moment right after waking. If your device reports a resting heart rate, that trend average is usually a better input than a single morning pulse check.

What throws the number off

Alcohol the night before, poor sleep, illness, heavy training the previous day, dehydration and heat can all elevate resting heart rate temporarily. A single reading taken the morning after any of these is not a reliable input for Karvonen; wait for a more typical morning, or lean on a multi-day average from a wearable, before recalculating your zone 2 range.

What the evidence actually shows

Zone 2's popularity online has run ahead of the underlying evidence in places, so it is worth separating what is well established from what is more speculative marketing.

Well established

That endurance athletes spend the large majority of their training time at low, easy intensities, roughly in this range, is one of the most consistently reproduced findings in endurance training research across sports and decades. That low intensity training drives capillary density, mitochondrial content and general aerobic capacity is also well supported by decades of exercise physiology work, not a new claim.

Less settled

Some specific claims circulating online, such as a precise heart rate cutoff where fat oxidation switches off entirely, or zone 2 training reversing metabolic disease on its own, go further than the underlying research currently supports. Zone 2 is a genuinely useful, well evidenced training intensity; it is not a singular metabolic switch or a substitute for overall training volume, sleep and diet.

Common mistakes

Training too hard for zone 2. This is the single most common error. Ego and impatience push the pace up into zone 3, which feels more productive in the moment but blunts the specific aerobic adaptations zone 2 is meant to drive.

Sessions that are too short. A 15 minute jog rarely does much at this intensity. Zone 2 needs duration to work, which is exactly why it demands patience.

Using percent of max without checking resting heart rate. If your resting heart rate is well below average for your age, percent of max will understate your true zone 2 range compared to Karvonen.

Expecting fast results. Mitochondrial adaptations build over months of consistent training, not weeks. Zone 2 is a base building tool, not a quick fix.

Dropping it once harder training starts. Zone 2 stays useful year round, not just during a base building phase. Cutting it out entirely once interval sessions begin usually shrinks the aerobic foundation those harder sessions depend on.

How coaches use a zone 2 heart rate calculator

For a coach, the hardest part of prescribing zone 2 is rarely the calculation, it is getting a client to actually stay in it instead of drifting into a harder, more satisfying effort. A clear bpm range, checked against a client's own resting heart rate, gives them something concrete to hold to.

Scraler attaches each client's zone 2 range to their profile once it is calculated, so every assigned cardio session carries the same bpm target automatically. See workout programming for how sessions and targets are built per client.