Karvonen
zones

Training zones from your heart rate reserve — the beats between rest and maximum — not just a slice of your maximum. Enter your age, your resting heart rate, and a maximum (measured or estimated), and get five %HRR zones in beats per minute, with the reserve they are built on.

How the math works

The Karvonen formula scales training intensity across your heart rate reserve — the span from resting to maximum heart rate — instead of taking a flat percentage of the maximum. It multiplies that reserve by the intensity you want, then adds your resting heart rate back on, so the zones start from where your heart actually idles.

The maximum heart rate is the one input worth measuring. A max-effort test or a lab value is the accurate source. Without one, the two age-based estimates carried here are Tanaka, HR_max = 208 − 0.7 × age, and the older Fox-Haskell convention, HR_max = 220 − age. Tanaka is the tighter of the two per its 2001 meta-analysis, and it is the default here.

The zone bands are the ACSM five-zone percentages, applied to the reserve rather than to the maximum. Because the resting heart rate is added back at every step, each Karvonen zone lands higher in beats per minute than the same percentage taken straight off the maximum — by exactly HR_rest × (1 − intensity). That gap is largest at rest and shrinks to zero at maximum effort.

Worked example

A 35-year-old runner with a resting heart rate of 60 bpm, using the Tanaka estimate. The maximum is 208 − 0.7 × 35 = 184 bpm, so the heart rate reserve is 184 − 60 = 124 bpm. Each zone is that reserve times the intensity, plus 60:

The same runner's Zone 2 is 110–129 bpm by plain percent-of-max, but 134–147 bpm by Karvonen — because the resting heart rate shifts every zone up. At the bottom of Zone 2 the gap is 60 × (1 − 0.60) = 24 bpm, narrowing to 18 bpm at the top. Heart rate is beats per minute, the same number everywhere; there is no imperial-versus-metric version of it. Units only re-enter when you pair a zone with pace — an easy Zone 2 effort might sit near 9:30–10:00/mi (5:54–6:13/km) for a 3:30-marathon runner (Scenario E2), and that pace has two unit forms while the heart rate has one.

When this calculator is wrong

Karvonen looks more individual than 220 − age because it folds in your resting heart rate. That is real, but it doesn't fix the other input. Unless your maximum is measured, the zones still ride on an estimate: the 220 − age convention carries a population standard deviation of about 10–12 bpm, and Tanaka is tighter but still off by 5–8 bpm for many people. That is enough to put a formula-built zone a full zone away from your real one, and an accurate resting heart rate can't rescue an inaccurate maximum. When the zones matter, do a max-effort test or use a lab value rather than an age estimate.

The exception is where the formula is already good enough: a new runner just starting easy-aerobic work. For a first pass it is fine, and it saves the effort of a max test they probably aren't ready for. Zone 2 built from an estimate is close enough to keep easy days easy while fitness — and a more honest set of numbers — builds.

• The resting heart rate has to be measured, not guessed. Take it on waking, lying still, before caffeine — not while sitting at a desk, where it can read 10–15 bpm high. The good news is the formula forgives a small error: at Zone-2 intensity, a 10-bpm resting mistake moves the target only about 3–4 bpm.
• Resting heart rate drifts with fitness. It falls as your aerobic base grows and rises with illness, heat, or under-recovery. A reserve computed in January is stale by spring — re-measure resting HR every few weeks and recompute.
• Medication and heart conditions break it. Beta-blockers and other rate-lowering drugs lower both resting and maximum heart rate and decouple heart rate from effort, so no reserve-based zone describes intensity. That's a clinician question, not an input you adjust.

What to do with the result

Use Zone 2 as the ceiling for easy and base-building runs, and keep most of your weekly volume under it. Confirm it with a talk test: if you can't speak in full sentences, you've drifted above Zone 2 regardless of what the watch says. Treat the estimated maximum as provisional — the first time you see a genuine max in a hard session or a race, plug that number in and the whole set of zones sharpens. Re-measure your resting heart rate every few weeks and recompute, since a fitter reserve moves every band. Recompute on a birthday too, when the age term shifts the estimate by a beat.

Common questions

What is the Karvonen formula?

It is a way to set training heart rate zones from your heart rate reserve — the difference between your maximum and resting heart rate — rather than from a flat percentage of the maximum. Target heart rate = (reserve × intensity) + resting HR. Named after the Finnish physiologist Martti Karvonen, whose 1957 study introduced the reserve method, it personalises the zones by starting from where your heart actually idles.

How do I calculate my target heart rate with the Karvonen method?

Subtract your resting heart rate from your maximum to get your reserve, multiply the reserve by the intensity you want as a decimal, then add your resting heart rate back. For a 35-year-old with a 184 bpm maximum and a 60 bpm resting rate, 60% intensity is (184 − 60) × 0.60 + 60 = 134 bpm, and 70% is 147 bpm — that's Zone 2.

Is the Karvonen formula more accurate than 220 minus age?

It's more individual, because it uses your measured resting heart rate, but it is only as accurate as the maximum you feed it. If that maximum is itself 220 − age, the zones inherit that formula's 10–12 bpm spread. The accuracy comes from measuring your maximum, not from the reserve step. Karvonen with an estimated max is a refinement, not a fix.

What resting heart rate should I use?

Your true resting rate: measured on waking, lying still, before caffeine or activity. A daytime seated reading can run 10–15 bpm high and pushes every zone up with it. The formula tolerates a small error — at easy-aerobic intensity a 10-bpm resting mistake shifts the target only 3–4 bpm — but a large one from a bad measurement is worth avoiding.

What's the difference between Karvonen zones and percentage-of-max zones?

Percent-of-max takes a fraction of your maximum heart rate directly; Karvonen takes the fraction of your reserve and adds resting HR back. Karvonen therefore lands higher — by exactly resting HR × (1 − intensity) at any intensity — so the two disagree most in easy zones and converge at maximum. For a 60 bpm resting rate, a 60% target is 24 bpm higher under Karvonen than under plain percent-of-max.

Does the Karvonen formula work if I'm on beta-blockers?

No. Beta-blockers and similar medications lower both resting and maximum heart rate and break the link between heart rate and effort, so a reserve-based zone no longer describes intensity. Use perceived effort or a talk test instead, and ask the prescribing clinician how to gauge training intensity while on the medication.