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Get your max heart rate and five training zones from age and resting heart rate using the Karvonen method. Free, no signup.
Heart-rate zones split your effort range into five bands, each driving a different adaptation — from easy aerobic base work in zone 2 to VO2-max intervals in zone 5. This calculator uses the Karvonen method, which factors in resting heart rate to personalize zones beyond a generic age formula.
Most of the endurance benefit for lifters comes from zone 2 — comfortable, conversational effort around 60–70% of heart-rate reserve. It builds the aerobic base and work capacity that make heavy sets recover faster, without the systemic fatigue that eats into strength training.
The classic mistake is drifting: easy days creep into zone 3 (too hard to recover from cheaply, too easy to force adaptation) while hard days aren't truly hard. Anchoring sessions to zones keeps the split honest — roughly 80% easy, 20% genuinely hard.
Target heart rate = resting HR + zone% × (max HR − resting HR). By working from heart-rate reserve instead of max HR alone, it scales zones to your current fitness — two people of the same age with different resting heart rates get different, more accurate zones.
It's a population average with an individual spread of ±10–15 bpm, so it can miss badly for any one person. If you've seen a higher number in a race or hard interval session, use that observed max instead.
Two or three 30–45 minute sessions per week improve recovery and work capacity with essentially no interference to strength — especially if you keep them truly easy and separate them from heavy leg work by a few hours.
Want the number to actually go up? Snap My Gym builds percentage-based programs around your lifts and tracks them automatically. More evidence-first training articles on the blog.