The Karvonen Formula — Zones from Your Heart-Rate Reserve
Karvonen sets training zones from your heart-rate reserve (max HR − resting HR), not a flat percentage of your max — so a fitter heart gets more accurate zones.
The simplest zones are just a percentage of your maximum heart rate. Karvonen improves on that by adding your resting HR back in: it works off the reserve between rest and max, so people with the same maximum but different fitness get different targets. It's why your watch's zones can differ from a friend's — and why Garmin and Polar can disagree. It's a better method, but it still leans on an estimated max HR, which carries its own ±10 bpm.
Karvonen adds your resting HR back in, so it works off your reserve (120 bpm), not a flat share of your max. Drop the resting slider — a fitter heart — and every zone shifts up. That's why a watch using Karvonen (Garmin's default with resting HR) shows different zones from one using % of max HR (Polar's default). Both still lean on an estimated max, which carries ±10 bpm of its own — read the whole thing as a range.
Why reserve, not just a percentage
Martti Karvonen and colleagues introduced the heart-rate-reserve idea in 1957. The reserve is the room between your resting and maximum heart rate — the range you can actually train across. A plain "70% of max" ignores your resting rate; Karvonen scales the intensity across the reserve and adds resting HR back, so 70% Karvonen lands higher than 70% of max, and moves as your resting HR drops with fitness.
That personalisation is real and useful. But the honest caveat stands: your maximum heart rate is almost always estimated (±10 bpm), and your resting HR has to be measured properly. Karvonen makes the zones fit you better; it doesn't remove the uncertainty in the anchor.
Good for
Personalised zones once you have a resting HR — more accurate at the edges than % of max.
Keep in mind
Needs a real resting HR and a max HR that is usually estimated (±10 bpm). Zones are still ranges.
Build zones that fit your heart.
The heart-rate calculator computes Karvonen zones from your resting HR, next to the % of max and threshold systems — with an honest max-HR range behind them.
Open the heart-rate calculatorKarvonen, Kentala & Mustala (1957) — Annales Medicinae Experimentalis et Biologiae Fenniae 35(3):307–315. A long-established method, not a single regression equation; implementation (heart-rate reserve, five zones) covered by our test suite. Full sourcing on the method page.
FAQ
What is the Karvonen formula?
The Karvonen formula sets a target heart rate from your heart-rate reserve: target = ((max HR − resting HR) × intensity) + resting HR. Because it adds your resting HR back in, it accounts for fitness — two people with the same max but different resting rates get different targets for the same effort.
Karvonen vs percentage of max heart rate — what’s the difference?
A plain "% of max HR" zone is just max × intensity. Karvonen works off the reserve (max − resting) and adds resting back, so its zones sit higher and shift with your resting HR. This is why a Garmin (which uses Karvonen when it has your resting HR) can show different zones from a Polar (which defaults to % of max).
What resting heart rate should I use?
Measure it at true rest — ideally first thing in the morning before getting up, averaged over a few days. A resting HR that is too high (measured after coffee or activity) will push every zone up. Wearables estimate it reasonably well overnight.
Is Karvonen more accurate?
It personalises the zones, which is an improvement over a flat percentage — but it still depends on your maximum heart rate, which for most people is an estimate carrying about ±10 bpm. So Karvonen sharpens the method, not the underlying uncertainty. Read your zones as ranges.
Related: the Tanaka max-HR formula · why "220 − age" is off · max heart rate for women.