Calculate heart rate training zones by age. Find your target heart rate ranges for different exercise intensity levels. Health data never leaves your device — every calculation runs locally in your browser.
Calculates Basal Metabolic Rate using the Mifflin-St Jeor equation with age, sex, height, and weight. Nutritionists use it for diet planning. Health data never leaves your device — every calculation runs locally in your browser.
Calculate body fat percentage using the US Navy circumference method. Enter waist, neck, height, and hip measurements. Health data never leaves your device — every calculation runs locally in your browser.
Compare baby weight and height against WHO median references by age and sex, shown as % above or below the median — a reference comparison, not clinical percentiles. Monitor your childs growth compared to population medians. Health data never leaves your device — every calculation runs locally in your browser.
Calculate customer churn rate by dividing customers lost by total customers. Monitor retention health for your subscription business. Numbers never leave your device — every calculation runs locally in your browser.
Calculate simple interest using principal, rate, and time. Find total interest earned and final amount for basic interest calculations. Figures never leave your device — every calculation runs locally in your browser.
Karvonen method: max HR = 220 − age, reserve = max − resting HR, then zones at 50–60% recovery, 60–70% fat-burn, 70–80% aerobic, 80–90% threshold, 90–100% max of reserve added back to resting. Example: age 35, resting 65 → max 185, reserve 120, Zone 2 ≈137–149 bpm.
Zone 2 (60–70%) burns the highest fat fraction — but higher zones burn more total calories per minute. For fat loss, total weekly volume in Zones 2–3 beats short Zone 5 bursts.
±10–12 bpm for most people; medications (beta blockers), fitness, and genetics shift it. For precise training, do a field test or lab VO2max — formulas are starting points.
80% of runs in Zone 2 (conversational pace), 20% harder. Beginners going too hard is the top cause of burnout and injury — slow builds the aerobic base.
No. All calculations run locally in your browser. No health data is transmitted or stored.
Running Pace Calculator
Compute running pace and speed from distance and time in km or miles. Check splits for a 5K tune-up — free, local, no signup.
Calories Burned Calculator
Estimate workout burn across running, cycling, swimming, yoga, and lifting from weight and duration. Price a 45-minute run in calories — free, local, estimate only.
Last updated October 2026