Zone 2 Heart Rate Calculator

Zone 2 is the heart-rate range corresponding to roughly 60-70% of your maximum heart rate (or 60-70% of heart-rate reserve via the Karvonen formula) and it has become the most discussed training intensity in endurance sport and longevity medicine over the last five years. The reason is straightforward: Zone 2 is the highest intensity at which fat remains the dominant fuel source and lactate is being cleared as fast as it is produced. It sits just below the first lactate threshold (LT1), the inflection point where blood lactate rises above resting values (around 2 mmol/L). The physiology behind Zone 2 was characterised in detail by Dr Iñigo San Millán at the University of Colorado, who showed that consistent Zone 2 work drives mitochondrial biogenesis - literally building more and more efficient mitochondria inside your muscle cells. More mitochondria means more capacity to oxidise fat, more metabolic flexibility (the ability to switch between fuel sources), and a higher first lactate threshold. Peter Attia popularized Zone 2 through his podcast and book Outlive, arguing that it is the single most important training modality for healthspan because mitochondrial decline is one of the hallmarks of aging.

The practical takeaway is the polarized 80/20 distribution that dominates every elite endurance training program from Norwegian cross-country skiing to Kenyan marathon running to world-tour cycling. Roughly 80% of weekly training time should sit in Zones 1-2 (mostly Zone 2), and the remaining 20% should be high intensity Zones 4-5 (lactate threshold cruise intervals and VO2 max work). Zone 3, the moderate 'tempo' zone, is deliberately minimised because it is too hard to recover from quickly and too easy to produce VO2 max gains - the worst of both worlds. Most amateur athletes invert this distribution, spending most of their time in Zone 3, which is why their fitness plateaus. A practical week might look like: Monday 60 min Zone 2, Tuesday 45 min VO2 max intervals, Wednesday 75 min Zone 2, Thursday rest or 30 min Zone 1, Friday 60 min Zone 2, Saturday 90 min Zone 2 long, Sunday 40 min threshold intervals. That is roughly 80% Zones 1-2 and 20% Zones 4-5.

Dr Phil Maffetone's MAF (Maximum Aerobic Function) method approaches the same problem from a different angle. The MAF formula is 180 minus your age, modified by your training status: subtract 10 bpm if you are new to exercise, returning from injury, or take medications; subtract 5 if you have been training consistently for 1-2 years; no change for 2+ years healthy and progressing; add 5 only if you are a competitive elite athlete or a very fit 60+ adult. The resulting number is a hard ceiling you are not supposed to exceed during aerobic-base work. Maffetone argues that even brief excursions above MAF compromise aerobic adaptation. In practice the MAF ceiling typically lands very close to the upper edge of Zone 2 calculated via Tanaka or Karvonen, so the two systems agree on the principle (train slow to go fast) and differ mostly in the exact bpm cap and the strictness of the prescription. The talk test is the simplest real-world check: if you can hold a full conversation in sentences without gasping, you are in true Zone 2. If you have to pause for breath, slow down. If you can only nose-breathe and still feel comfortable, you are right in the sweet spot. Most amateurs run their Zone 2 5-15 bpm too hard because true Zone 2 feels embarrassingly easy. That is the point.

Zone 2 vs Other Training Methods

How to Use This Calculator

1. 1. Pick Your Sex: Women aged 35-65 should pick Gulati; otherwise Tanaka is the safest default for accurate max HR.
2. 2. Choose a Calculation Method: Karvonen if you know your resting HR (best). Maffetone MAF for a strict do-not-exceed ceiling. %Max HR if you do not have resting HR data.
3. 3. Pick a Max HR Formula: Tanaka for most adults, Gulati for women, Nes/HUNT for active over-40s. We compute all four every time so you can compare side-by-side.
4. 4. Enter Age, Resting HR, and Weekly Hours: Age in years, true morning resting HR, and how many hours of cardio you train per week (we use this for the 80/20 prescription).
5. 5. Apply Zone 2 to Training: Use the midpoint as your target and the high number as your ceiling. Aim for 3-5 Zone 2 sessions of 45-90 minutes per week. Trust the talk test - if you cannot speak in sentences, slow down.

Zone 2 Use Cases & Linked Calculators

Pro Tips for Zone 2 Training

• • Trust the talk test: If you cannot speak in sentences, you are above Zone 2. Most amateurs run Z2 5-15 bpm too hard.
• • Minimum 45 minutes per session: Mitochondrial signaling needs sustained submaximal stress. Aim for 60-90 minutes per Zone 2 session.
• • Get a chest strap: Wrist optical sensors lag 10-30 seconds. Polar H10, Garmin HRM-Pro, or Wahoo TICKR are accurate within 1-2 bpm.
• • Accept cardiac drift: HR will climb 5-15 bpm over 60-90 minutes even at constant power. Slow down to keep HR in zone.
• • 3-5 sessions per week: Zone 2 is low-stress enough to do almost daily. Most plans use 3-5 Z2 sessions plus 1-2 high-intensity.
• • Be patient: Mitochondrial adaptation takes 8-12 weeks of consistent work to show up in performance. Stay the course.
• • Re-test every 3-6 months: As Zone 2 fitness improves your resting HR drops and you can hold higher power at the same HR.