Training with purpose: understanding heart rate zones
Heart rate zones divide your training intensity into bands, each associated with different physiological adaptations. Training entirely at one intensity — typically moderate, "comfortable" effort — is one of the most common reasons people plateau despite consistent training; deliberately varying intensity across zones tends to produce better results for most goals.
This calculator estimates your maximum heart rate using the Tanaka formula (208 − 0.7 × age), published in 2001 from a large meta-analysis and generally found to be more accurate across age groups than the older "220 minus age" rule of thumb still seen on many gym cardio machines.
What each zone does
Zone 1 (50-60% of max) is light, conversational-pace effort, used for warm-ups, recovery, and active rest days. Zone 2 (60-70%) is the classic "fat-burning" zone — sustainable for long durations and a major contributor to aerobic base fitness. Zone 3 (70-80%) is moderately hard, improving cardiovascular efficiency, while zone 4 (80-90%) is genuinely challenging, anaerobic-threshold-style effort that builds speed and lactate tolerance. Zone 5 (90-100%) is maximal effort, sustainable only briefly, used for sprint and high-intensity interval work.
A practical training split
Many evidence-informed training plans for general fitness or endurance allocate roughly 70-80% of weekly training time to zones 1-2, with the remainder split between zone 3 and the harder zone 4-5 work — often called a "polarized" approach. This avoids the common trap of doing too much moderate-intensity (zone 3) training, which can be fatiguing without delivering the strongest aerobic or high-intensity adaptations of either extreme.