Karvonen Formula: A Runner's Guide to Heart Rate Training

A common pattern in heart rate training: a recreational runner with a few years of mileage in the legs still goes home from every easy run feeling cooked. They use the classic “220 minus age” shortcut, multiply by 70%, and train at the number it spits out. The maths looks fine on paper. The legs disagree. Switch to the Karvonen formula, account for a properly measured resting heart rate, and the real easy target often drops by 5 to 10 bpm. Within a fortnight the easy runs feel easy, weekly mileage rises, and the next 10 km drops a chunk. The maths does the work motivation cannot.

This guide explains the Karvonen formula in plain English, shows you how to apply it to running, and gives you worked numbers you can copy straight onto your watch.

What the Karvonen Formula Actually Calculates

The Karvonen formula uses your heart rate reserve, not your maximum heart rate, to set training targets. Heart rate reserve is the gap between how slow your heart can go at rest and how fast it can beat at full effort. That gap is where all your training happens. The formula is straightforward:

Target HR = (HRmax – HRrest) x intensity% + HRrest

The bracketed part is your heart rate reserve. You take a percentage of that, then add your resting heart rate back on top. The result is a target heart rate that respects your individual physiology, not a generic average. Martti Karvonen and his colleagues at the University of Helsinki published this method in 1957 in Annales Medicinae Experimentalis et Biologiae Fenniae, and it has been a coaching staple ever since.

The reason coaches still use it nearly 70 years later is simple. Two runners with the same maximum heart rate can have wildly different resting heart rates. A trained 40-year-old with a HRrest of 45 bpm has a much larger reserve than a sedentary 40-year-old with a HRrest of 75 bpm. Treat them the same and you will overcook one and undercook the other.

Why “220 Minus Age” Lets Runners Down

The most common shortcut for setting heart rate targets multiplies your estimated HRmax by an intensity percentage. The estimate usually comes from “220 minus age”, a rule that was never peer-reviewed and was popularised more by gym posters than research. Tanaka and colleagues reviewed 351 studies in the Journal of the American College of Cardiology in 2001 and reported a standard deviation of roughly 10 bpm to 12 bpm around any age-based prediction. That is a margin big enough to put you in entirely the wrong training zone.

The 220 – age method also ignores fitness. Your HRmax barely changes with training, but your HRrest plummets as you get fitter. A new runner might start with a HRrest of 70 bpm and reach 50 bpm within a year. The 220 – age method cannot see that change. The Karvonen heart rate formula catches it immediately because HRrest is baked into the calculation.

There is a second issue. At low intensity percentages, the two methods diverge sharply. At 60% of HRmax, a 40-year-old runner would target 108 bpm. Using Karvonen with the same runner and a HRrest of 50 bpm, 60% of heart rate reserve plus HRrest gives 128 bpm. That is a 20 bpm difference for what should be the same effort. Train at 108 bpm and you will not stimulate the aerobic system at all. Train at 128 bpm and you will.

A Worked Example You Can Copy

Take a 40-year-old runner with a measured HRmax of 180 bpm and a HRrest of 50 bpm. Plug those into the Karvonen formula at 70% intensity:

• Heart rate reserve = 180 – 50 = 130 bpm
• 70% of HRR = 130 x 0.70 = 91 bpm
• Target heart rate = 91 + 50 = 141 bpm

Now run the same maths at the four key training intensities:

• Easy / recovery (60% HRR): 130 x 0.60 + 50 = 128 bpm
• Aerobic / steady (70% HRR): 130 x 0.70 + 50 = 141 bpm
• Tempo / threshold (80% HRR): 130 x 0.80 + 50 = 154 bpm
• VO2 max (90% HRR): 130 x 0.90 + 50 = 167 bpm

The same runner using 220 – age would land on 109, 126, 144 and 162 bpm for the same four zones. Every value is lower, which means every session would be run too soft to deliver the intended adaptation. That is the practical cost of skipping the resting heart rate input.

If you would rather not crunch the numbers by hand, the RunReps pace to heart rate zone calculator applies the Karvonen formula for runners and returns all five zones in one click.

How to Find Your True HRmax

The Karvonen formula is only as good as the numbers you feed it, and HRmax is the bigger of the two inputs. There are three ways to get it, in descending order of accuracy.

Laboratory test

A graded exercise test in a sports science lab is the gold standard. You run on a treadmill while load increases until you reach volitional exhaustion. The peak heart rate is your true HRmax. Costs vary, but expect to pay between £80 and £200 in the UK. If you race seriously or have any cardiac history, this is the route to take.

Field test

If a lab is not realistic, a hard field effort gets you close. Warm up for 15 minutes. Run a flat 800 m hard. Recover with two minutes of jogging. Run a second 800 m harder than the first, and sprint the final 200 m. The peak number on your watch is a reliable HRmax estimate for most runners. A 6 minute hill repeat run at maximum effort works equally well.

Repeat the test on a different day. If the numbers agree within 2 bpm, trust the higher reading. Do not test on hot days or after a hard week, because both will suppress the result.

Age-graded estimate

If you cannot test, use a better formula than 220 – age. Tanaka’s regression equation (208 – 0.7 x age) is more accurate across all age groups. A 40-year-old lands on 180 bpm with both methods by coincidence, but a 60-year-old gets 166 bpm rather than 160 bpm, which makes a meaningful difference. Treat any age-based number as a starting point and adjust once you have race data.

How to Measure Your True HRrest

Your resting heart rate is easier to measure but harder to measure well. The protocol that returns the cleanest number is the morning resting measurement.

Wear a heart rate strap to bed or keep your watch on. When you wake naturally, before you sit up, before coffee, before checking your phone, look at your heart rate. Record it. Do this for seven mornings. Drop the highest and lowest readings. Average the remaining five. That number is your HRrest.

A few things ruin the reading. Alarms spike heart rate. Caffeine the night before pulls it up. Alcohol the night before pulls it up further still. A poor night’s sleep will push it above your true value. If you have been ill, wait a week after symptoms clear before remeasuring.

For most trained adult runners, HRrest sits between 40 and 60 bpm. A reading above 70 in a trained runner usually means under-recovery, not low fitness. Track it weekly. A persistent rise of more than 5 bpm above your normal is a useful early warning that you are heading for a flat patch or a bug.

Applying Karvonen Zones to Real Running Sessions

Once you have the numbers, every session has a target. The zones below use the heart rate reserve percentages most coaches teach, and they map directly to the workouts you already do.

Easy runs (50-65% HRR)

Most of your weekly mileage lives here. Easy runs build aerobic capacity, mitochondrial density and capillary networks. If your easy heart rate keeps drifting above the upper bound, slow down. The discipline of staying inside this zone is the single biggest unlock for new and intermediate runners.

Steady aerobic (65-75% HRR)

This is the zone for long runs once you have a base, and for the bulk of marathon-specific work. It feels controlled but not conversational. You can speak in short sentences. Sustained effort here builds fat oxidation and endurance.

Tempo and threshold (75-85% HRR)

Tempo runs and lactate threshold intervals sit in this band. Effort feels comfortably hard. Sessions like 4 x 8 minutes at threshold, or a 20 minute continuous tempo, target your lactate clearance and race-specific economy from 10 km to marathon.

VO2 max (85-95% HRR)

Short, sharp intervals. Think 5 x 3 minutes hard with 2 minutes jog recovery. These efforts push your maximum oxygen uptake, and heart rate often lags the effort, so use HR as a confirmation rather than a target. Pair this work with the RunReps pace calculator so you have both pace and HR anchors.

Anaerobic and neuromuscular (95-100% HRR)

Strides, hill sprints and 30 second reps. Heart rate is not a useful guide here because the efforts are too short to drive the heart to its ceiling. Use feel and pace instead.

If you want a deeper walk-through of how these bands fit a full training week, our companion piece on heart rate zones for runners covers session design in more detail.

Find Your HR Zone

Where the Karvonen Formula Falls Short

The Karvonen heart rate formula is the best simple model for target heart rate calculation in runners, but it is still a model. Three caveats are worth knowing.

First, individual variation does not disappear. Two runners with identical HRmax and HRrest can have different lactate thresholds. If your tempo runs feel either too easy or too hard at 80% HRR, treat the zone as a starting point and shift it 2-3% in either direction based on lab testing, a 30 minute time trial, or a coach’s eye.

Second, cardiac drift will mess with hot or long runs. Research published in Medicine & Science in Sports & Exercise has shown that heart rate rises 5-10 bpm during sustained efforts in heat, with no change in actual workload (Coyle and Gonzalez-Alonso, 2001). If you train in summer, run by feel and pace on hot days, and use the Karvonen target only on cool mornings.

Third, medications and recovery status both move the numbers. Beta blockers cap HRmax and skew every calculation. So does fatigue from a heavy training week. If your numbers feel off, retest both inputs before retuning the zones.

None of these caveats break the formula. They just remind you that heart rate is one data stream among several. Pair it with perceived effort, pace and weekly load, and the Karvonen formula does what it has done since 1957: give you a sharper, fairer target than any single age-based estimate can deliver.

What Runners Ask About the Karvonen Formula

Is the Karvonen formula more accurate than 220 minus age?

Yes, for most runners. The 220 – age method ignores resting heart rate and is built on a regression that carries roughly 10-12 bpm of error per Tanaka’s 2001 review. The Karvonen formula accounts for individual fitness through HRrest, so it lands closer to your true training target, especially at low and moderate intensities where the two methods diverge most.

What intensity should I use for easy runs with the Karvonen formula?

Most runners get the best aerobic stimulus at 60-70% of heart rate reserve. If you are new to running or returning from a break, sit at the lower end. Once you have a few months of consistent training, the upper end of that band feels natural and still respects the easy-day principle. If you cannot hold a conversation, you are above the zone, regardless of what the number says.

Do I need to retest my HRmax and HRrest each year?

HRmax declines gradually with age, roughly 0.7 bpm per year on average, so a retest every two or three years is plenty. HRrest changes faster, particularly when your training volume shifts. Measure HRrest monthly during heavy training blocks and quarterly the rest of the year, so the Karvonen formula for runners always uses fresh inputs.

Can I use the Karvonen formula on a treadmill?

Yes, with one tweak. Heart rate at a given pace tends to run 3-5 bpm higher indoors because of reduced cooling and lower mechanical efficiency. Either set the treadmill at 1% incline to mimic outdoor effort, or accept that you will see slightly higher HR at the same Karvonen zone. The target heart rate calculation does not change. Combine it with the RunReps running plan generator so your treadmill sessions still progress in line with the rest of your week.

This article is for informational purposes only and does not constitute medical advice. Heart rate training carries individual risk. If you have a cardiac condition, take prescribed medication that affects heart rate, are pregnant, or are new to running, consult a qualified healthcare professional before testing HRmax or starting a heart rate based training programme.