Karvonen Formula - Target Heart Rate Calculator

The Karvonen formula works out heart rate training zones from your heart rate reserve rather than from your maximum heart rate alone. Heart rate reserve, usually shortened to HRR, is the gap between your maximum heart rate and your resting heart rate. It is the range your heart actually has available to work in.

The formula itself is short: target heart rate = ((max HR - resting HR) x intensity) + resting HR. The intensity is the percentage you want to train at, so the 70% bound of a zone uses 0.70. Adding the resting heart rate back at the end is the step that makes it Karvonen rather than a simple percentage, and it is the step most people miss when they work it out by hand.

That single addition is why the method exists. A percentage of max heart rate treats every runner with the same maximum identically, whether their resting heart rate is 45 or 75. Karvonen does not: a fitter runner with a lower resting pulse has a wider reserve, so the same percentage lands on a different number of beats. The calculator above defaults to this method for that reason.

The formula was published by Martti Karvonen, a Finnish physiologist, and it is sometimes called the Karvonen method or the heart rate reserve method. All three names describe the same calculation.

Take a 35-year-old runner with a resting heart rate of 55 bpm, which is the calculator's default. Maximum heart rate is estimated at 184 bpm using the Tanaka formula (208 - 0.7 x age), so heart rate reserve is 184 - 55 = 129 bpm.

Zone 2 runs from 60% to 70% of that reserve. The lower bound is (0.60 x 129) + 55 = 132 bpm, and the upper bound is (0.70 x 129) + 55 = 145 bpm. Every other zone is the same arithmetic with a different pair of percentages.

You can measure your maximum heart rate instead of estimating it, and the calculator accepts a measured value. A field test is more accurate than any age formula: warm up thoroughly, run hard for three minutes, recover for three, then run all out for one more. The highest reading you see is close to your true maximum. Measure resting heart rate first thing in the morning, before you get out of bed.

Both methods are offered above, and they disagree by more than most runners expect. Run the same 35-year-old through the simple percentage method and Zone 2 comes out at 110-129 bpm. Karvonen puts it at 132-145 bpm. The top of the zone differs by 16 bpm and the bottom by 22.

The gap is not a rounding artefact and it does not close at other ages. A 50-year-old with a resting heart rate of 70 gets a Zone 2 of 132-142 bpm from Karvonen and 104-121 bpm from percentage of max. A 25-year-old resting at 60 gets 139-152 against 115-134. The percentage method sits roughly 20 bpm lower in every case, because it never accounts for the floor your heart rate starts from.

This matters most for easy running, which is where runners spend most of their time and where the two models are furthest apart. A runner following percentage-of-max Zone 2 is being told to hold 110-129 bpm, which for many people is a walk rather than a run. That is the usual reason easy-run heart rate targets get abandoned as unrealistic within a fortnight.

Percentage of max is not wrong, it is just blunter. It is a reasonable starting point when you do not know your resting heart rate, and nothing else. If you know both numbers, use Karvonen.

Around 80% of your weekly running should sit in Zone 2, the aerobic base zone. This is consistently lower than recreational runners expect, and holding it takes discipline rather than fitness. The remaining 20% covers threshold work in Zone 4 and interval sessions in Zone 5. Zone 3 is the one to be wary of: it is comfortable enough to live in and hard enough to accumulate fatigue, without delivering the benefit of either neighbour.

Heart rate lags effort by 30 seconds to a couple of minutes, so it is a poor guide over a short interval and a good one over a long steady run. On hill reps or 400s, run to effort or pace and read the heart rate afterwards. On an easy hour, the number in front of you is the more honest signal.

Zones move with conditions. Heat, dehydration, altitude, poor sleep and accumulated training load all push heart rate up at the same pace, sometimes by 10 bpm or more. That is the zones working correctly rather than failing: the effort genuinely is higher. If you want to see how a given pace maps onto a zone on a particular day, the pace to heart rate zone translator does that conversion, and the training paces calculator sets the pace targets those zones should correspond to.

For the longer explanation of where the formula came from, how heart rate reserve behaves as fitness improves, and how to use zones across a training block, read the full guide to the Karvonen formula and heart rate training. To put the zones into a structured week, the running plan generator builds a plan around them.

Karvonen depends on two numbers, and one of them is usually estimated. The Tanaka formula (208 - 0.7 x age) is more accurate than the older 220 - age for adults over 30, but it is still a population average: individual maximum heart rates vary by 10-20 bpm either side of any age prediction. If your estimated maximum is wrong, every Karvonen zone built on it is wrong by the same proportion.

Joe Friel's model, the third option above, avoids the problem by anchoring to lactate threshold heart rate instead. LTHR is measured rather than predicted, so it does not inherit an age formula's error. Find it with a 30-minute time trial at the hardest effort you can sustain: your average heart rate over the final 20 minutes is close to your LTHR. The model then splits into seven zones rather than five, with more resolution around threshold, which is where race-specific training lives.

For most runners Karvonen is the right default. If you race seriously, know your LTHR, and want zones that discriminate between sub-threshold and super-threshold work, use Friel instead.