Anaerobic Threshold Calculator
Enter your age to estimate your anaerobic threshold heart rate using three validated maximum-heart-rate formulas (Fox, Nes, or Tanaka). Add your resting heart rate for Karvonen-based zones, or enter a measured LTHR from a 30-minute field test for precise, personalized training bands. All five zones update live as you type.
Formula
Worked example
A 35-year-old with resting HR 60 bpm: Tanaka max HR = 208 - 0.7 x 35 = 183.5 bpm. Anaerobic threshold at 85% = 183.5 x 0.85 = 156 bpm. HR reserve = 183.5 - 60 = 123.5 bpm. Zone 2 ceiling (83% max HR) = 152 bpm. Zone 4 lower bound (95% max HR) = 174 bpm.
What is the anaerobic threshold?
The anaerobic threshold (AT), also called the lactate threshold or LTHR, is the exercise intensity at which your body begins producing lactic acid faster than it can clear it. Below the threshold, your muscles run primarily on oxygen (aerobic metabolism) and can sustain effort for hours. Above it, lactate accumulates rapidly, causing the familiar burning sensation and forcing you to slow down within minutes. The threshold typically falls between 80% and 95% of maximum heart rate, with recreational athletes near the lower end and highly trained endurance athletes at the upper end. Knowing your AT is the foundation of effective training zone prescription for running, cycling, rowing, and triathlon.
How to estimate your anaerobic threshold heart rate
Three methods are widely used. First, you can estimate it from age-based maximum heart rate formulas - the Tanaka formula (208 - 0.7 x age) is the most validated for adults and gives a reasonable starting point. Second, you can conduct a 30-minute all-out field test: after a warm-up, run or cycle at the hardest pace you can sustain for 30 minutes while recording heart rate, then average the last 20 minutes. That average is your LTHR. Third, a sports physiology lab can measure blood lactate at graduated intensities to pinpoint where it reaches 4 mmol/L, the traditional "OBLA" (onset of blood lactate accumulation) cutoff. Field tests are sufficiently accurate for most athletes and far more accessible than lab testing.
Training zones and why they matter
Once you know your AT, the standard 5-zone model gives you a coherent training framework. Zone 1 (recovery, below 68% of max HR) is used for easy days between hard sessions. Zone 2 (69-83% max HR) is the aerobic base zone where fat oxidation and mitochondrial density improve - most long, slow distance work targets this zone. Zone 3 (84-94% max HR) is tempo pace, hard enough to stress the lactate clearance system but sustainable for 20-60 minutes. Zone 4 (95-99% max HR) sits right at and just below the threshold - training here directly raises the AT over time, allowing you to sustain more effort aerobically. Zone 5 (100% and above) targets VO2 max and is only sustainable for a few minutes. The most common training error is doing Zone 2 work at too high a heart rate, drifting into Zone 3 and accumulating chronic fatigue without the aerobic base adaptations that come from genuine low-intensity work.
The Karvonen method and heart rate reserve
The Karvonen (heart rate reserve) method refines training intensity by accounting for individual resting heart rate. Heart rate reserve is simply maximum HR minus resting HR. A target intensity is then: (reserve x fraction) + resting HR. Because someone with a resting HR of 40 bpm has a larger reserve than someone at 70 bpm, their Zone 2 ceiling in absolute bpm will also be higher for the same physiological intensity. A Karvonen 85% effort is often 5-10 bpm higher than a straight 85% of max HR calculation, which makes the two methods a useful cross-check: if they align closely, you can be more confident in the zone boundaries. Enter your resting heart rate in this calculator to see the comparison.
Standard 5-zone heart rate training model
| Zone | Name | % Max HR | % LTHR | Primary benefit |
|---|---|---|---|---|
| 1 | Recovery | < 68% | < 81% | Active recovery, technique work |
| 2 | Aerobic base | 69-83% | 82-89% | Fat oxidation, aerobic capacity, long slow runs |
| 3 | Tempo | 84-94% | 90-94% | Lactate clearance, race pace prep, stamina |
| 4 | Threshold | 95-99% | 95-102% | Raise LTHR, improve sustained power |
| 5 | VO2 max | >= 100% | > 102% | Maximal oxygen uptake, top-end speed |
Percentages relative to maximum heart rate (max HR method) or lactate threshold HR (LTHR method). Zones shift upward when using measured LTHR.
Frequently asked questions
What is the difference between anaerobic threshold and lactate threshold?
In practical sports science the terms are used interchangeably. Technically, the lactate threshold is the first point at which blood lactate begins rising above baseline (around 2 mmol/L), while the anaerobic threshold or OBLA (onset of blood lactate accumulation) is the higher intensity at which lactate rises steeply (around 4 mmol/L). For training zone purposes, LTHR usually refers to the second, higher point, which is what this calculator estimates.
Which max HR formula should I use?
Tanaka (208 - 0.7 x age) is the most validated for adults and has lower error than the classic Fox formula (220 - age), particularly for people over 40 where Fox tends to underestimate. However, all formulas have a standard deviation of roughly 10-11 bpm, so measuring your actual max HR in a graded exercise test or replacing the estimate with a measured LTHR from a field test gives more accurate zones.
How do I conduct a 30-minute field test?
Warm up for 10-15 minutes, then run or cycle at the hardest pace you can sustain for exactly 30 minutes. Keep pace as even as possible. Record heart rate throughout, then average your heart rate over the final 20 minutes of the effort. That average is your LTHR. Test conditions matter: use a flat course or indoor trainer, avoid heat, and ensure you are well rested beforehand. Repeat every 8-12 weeks to track adaptation.
Why does training at Zone 2 feel so easy?
Zone 2 heart rate (roughly 69-83% of max HR) is designed to feel genuinely comfortable - conversational pace. Many athletes habitually train too fast, spending most time in Zone 3 instead. True Zone 2 effort builds mitochondrial density, fat-burning efficiency and cardiac stroke volume over months of consistent training, but these adaptations require staying below the threshold where lactate begins to accumulate. If Zone 2 feels too slow, it is probably correct.
Can I use heart rate zones for cycling and swimming as well as running?
Yes, but your threshold HR will differ slightly by sport. Running threshold HR tends to be highest because large muscle groups and weight-bearing effort drive greater cardiovascular demand. Cycling LTHR is typically 5-8 bpm lower, and swimming even lower still due to horizontal posture and water cooling. For best accuracy, run a separate field test for each primary sport.
How does fitness level affect anaerobic threshold?
As aerobic fitness improves, the anaerobic threshold rises as a percentage of maximum heart rate. A sedentary person may reach the threshold at 60-70% of max HR; a trained endurance athlete may sustain effort up to 90-95% aerobically. This is why training specifically at threshold intensity (Zone 4 work) is effective at raising performance - it directly shifts the point at which lactate accumulates, allowing faster sustainable paces at the same heart rate.