Karvonen, Kentala and Mustala introduced the concept of heart rate reserve (HRR) in a 1957 paper. HRR is maximum heart rate (HRmax) minus resting heart rate (RHR).
The free heart rate zone calculator does both methods for you: enter a resting heart rate for Karvonen zones, or leave it out for %Max HR zones.
Another method favoured by sports watches, %Max HR, needs only one estimated maximum, usually 220 minus age. Handy as you know your age but less handy when you consider the formula is likely wrong for you.
The Implications of Incorrect Assumptions
Resting heart rate matters because it defines one end of the workable range.
A maximum of 185 bpm and a Z2 range of sixty to seventy per cent places an easy effort in different zones depending on the method, as the table below shows.
| Method | Resting heart rate | 60% | 70% |
|---|---|---|---|
| %Max HR | not used | 111 bpm | 130 bpm |
| Karvonen | 60 bpm | 135 bpm | 148 bpm |
| Karvonen | 75 bpm | 141 bpm | 152 bpm |
Neither method uses the more precise alternatives that rely on lactate or ventilatory threshold estimates; those are covered in heart rate training zones. Both are estimates rather than measurements, and HRR tracks oxygen uptake reserve more closely than the %Max HR method does.
Why the %Max HR method is still the default
%Max HR needs one number: an age. Karvonen also needs an estimated resting heart rate. %Max HR is easier, and that is the reason it is widely used in sports tech.
The one number it does ask for, age, commonly leads to a wrong HRmax. Robergs and Landwehr found no research behind 220 minus age in a 2002 review, and the formula is commonly cited as carrying a standard error of seven to twelve beats per minute.
An error of that size can easily place an effort in the wrong zone.
When Karvonen earns its place
- Endurance athletes in their forties and fifties, runners whose resting rate has fallen across a training block, and anyone with an unusually high resting heart rate for other reasons are most impacted when using the %Max HR method.
- Resting heart rate falls as fitness improves, often within weeks. If RHR is monitored or automated, the Karvonen targets move with it; the %Max HR method only moves when the maximum is re-measured, and few watches do that separately for each sport.
Calculating your own zones
Resting heart rate comes from a morning reading averaged over several days, or a wearable’s overnight figure. Maximum heart rate should be measured, not estimated, e.g. the highest value from a race or hill session is usually close, whereas an age-based estimate can still be out by seven to twelve beats per minute. Maximum heart rate is also sport-specific: cycling and swimming typically produce a lower measured maximum than running or cross-country skiing, and few watches or apps record a separate maximum per sport.
The free Karvonen heart rate zone calculator turns both figures into bpm targets for the watch, and is worth updating as your fitness changes.
Quick answers
Is the Karvonen formula more accurate than %Max HR?
HRR correlates more closely with oxygen uptake reserve than the %Max HR method does, making it the better proxy for training intensity, though neither measures a lactate or ventilatory threshold directly.
Should I trust my watch's default heart rate zones?
Most watches default to the %Max HR method for convenience, not accuracy. If the maximum behind it was estimated from age rather than measured, it likely carries the seven-to-twelve-beat-per-minute error commonly cited for 220 minus age, following Robergs and Landwehr’s 2002 review.
Do heart rate zones change as fitness improves?
Under Karvonen, often, since a falling resting heart rate lowers the target and the calculation is worth revisiting periodically. Under the %Max HR method, zones move only when the maximum is re-measured, and few watches do that separately for each sport.
This article is for informational purposes only and is not a substitute for guidance from a doctor or certified trainer.
Last Updated on 1 November 2026 by tfk the5krunner
Small things I always use
- Garmin 90-degree charging adapter: Charges your Garmin from any USB-C cable. Essential when travelling. I use one.
- Body Glide: The blue anti-chafe stick swimmers and runners carry. I use it.
- Speedo earplugs: Fewer ear infections and no cold-water dizziness. I use them.
- Dryrobe Advance: My winter changing robe for open-water swims. I use one. A cheaper option is the AONYIYI changing robe.
- Maurten: Race fuel that stays easy on the stomach. I use them.
- Beet It Sport nitrate shots: Beetroot shots I take in the days before a race. I use them.
- Garmin charging puck: The quickest way to top up before a session. I use one.
- Injinji: Toe socks that stop rubbing, so you run more. I use them.
- Ultimate toe protectors: Stop black toenails on long runs. They work. I use them.
- Compressport R2 v2 calf sleeves: My calf sleeves of choice. I use them.
- Cellucor C4: My pre-workout before hard sessions.
- TPU tubes: Schwalbe Aerothan, Tubolito and Pirelli SmarTube. Light, tiny spares. I use all three.
- G8 insoles: Adjustable insoles that are good. I use them.
- Cycplus Cube: A 97g electric pump that gets a road tyre rideable in two minutes. I carry one. 5% off with code THE5KRUNNER.
Watches and sensors
- Polar H10: My daily driver for waking HRV.
- Polar Verity Sense: My backup arm-worn HR sensor.
- Nomad bedside charger: Charges my iPhone and Apple Watch overnight. I use it, and many of their bands.
- Train.Red: The best muscle oxygen sensor I’ve used.
- Tymewear: Accurate heart rate and reliable ventilatory zones. I use it to pace endurance rides over an hour.
- Garmin Forerunner 970: A pro-grade triathlon watch. I use this.
- Apple Watch Ultra 4: My daily smartwatch. No phone needed on rides.
- Garmin Fenix 9 Pro: I’ve just bought one.
On the bike
- Continental GP5000 for everyday riding, and Aero 111 on the front for special occasions.
- Helmets: Specialized S-Works Evade 3 for road riding, and Rudy Project Wing for TT-style races. I use both.
- Ravemen FR300: A front light that mounts under your Garmin or Wahoo. I use one.
- Wahoo TRACKR Radar: I use it on one bike and Varia on the other. They perform the same.
- Garmin Varia RTL515: Radar that warns you of cars from behind. I use this model.
- Wahoo ELEMNT Roam 3: The bike computer that’s easy to use. I use mine on most rides.
- Favero Assioma Pro RS2: Accurate power pedals that swap easily between bikes. I use this model.
Home and indoor training
- NPE Runn: Makes my basic treadmill smart, sending more accurate speed and distance to my watch and Zwift. I use it.
- Google Wifi: Keeps Zwift connected in my pain cave. I use it.
- Apple TV 4K: Zwift on the big screen. I use two.
- Google Nest Doorbell (wired, 2nd gen): My video doorbell, running in both Google Home and Apple Home. I use it.
Health, recovery and sleep
- FreeStyle Libre 3 Plus: Shows how my blood sugar responds to diet.
- hDrop: Measures my sweat loss in summer and indoors.
- Fourth Frontier Zone: Checks my heart under load in hard sessions.
- Kineon MOVE+: Red and infrared light for sore knees, Achilles and other joints after hard training. I use it.
- Oura Ring 5: My partner’s recovery tracker of choice.
- Eight Sleep: A cooling mattress cover my partner and I use nightly.
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tfk is the founder and author of the5krunner, an independent endurance sports technology publication. With 20 years of hands-on testing of GPS watches and wearables, and competing in triathlons at an international age-group level, tfk provides in-depth expert analysis of fitness technology for serious athletes and endurance sport competitors. See the gear tfk uses. ID
I found that the Joe Friel method of defining zones as a percentage of LT2 is more closely aligned to my RPE.
https://www.trainingpeaks.com/learn/articles/joe-friel-s-quick-guide-to-setting-zones/
yes. i used to use that method (its mentioned in the link from this post)