ProReckoner's fitness calculators are built for personal trainers, gym coaches and anyone serious about their training. Tools cover body metrics (BMI, body fat, ideal body weight, BMR), energy and nutrition (TDEE, macro splits, calorie burn by activity), training science (one rep max, volume load, rest periods) and progress planning (weight trend analysis, target date calculator, heart rate training zones). All formulas reference peer-reviewed research and current exercise science guidelines.
Body Metrics
3 toolsBMI + Body Fat %
BMI classification plus estimated body fat percentage using the Deurenberg formula. Breaks down lean mass and fat mass.
BMI = Weight (kg) ÷ Height (m)²
BF% = (1.20 × BMI) + (0.23 × Age) − (10.8 × sex) − 5.4
BMI limits: BMI doesn't distinguish muscle from fat — athletes often appear "overweight". Use alongside body fat % for a full picture.
Ideal Body Weight (IBW)
Estimated ideal weight using Devine, Robinson and Hamwi formulas, plus healthy BMI weight range for your height.
Devine (M): 50 + 2.3 × (inches over 5ft)
Devine (F): 45.5 + 2.3 × (inches over 5ft)
Devine (1974) is the most widely used — originally developed for drug dosing. Robinson (1983) and Hamwi (1964) offer alternative estimates. Use healthy BMI range as a practical target for fitness goals.
Basal Metabolic Rate (BMR)
Calories burned at complete rest using Mifflin-St Jeor and Harris-Benedict formulas. The foundation for calculating TDEE.
Mifflin (M): (10×W) + (6.25×H) − (5×A) + 5
Mifflin (F): (10×W) + (6.25×H) − (5×A) − 161
Mifflin-St Jeor (1990) is the most accurate for general population — validated in multiple studies. Harris-Benedict (1984 revision) remains widely used but overestimates by ~5% on average.
Energy & Nutrition
3 toolsTDEE Calculator
Total Daily Energy Expenditure — your maintenance calories. Provides fat loss, maintenance and lean bulk targets.
TDEE = BMR × Activity Factor
Activity factors (Mifflin-St Jeor): Sedentary 1.2 · Light 1.375 · Moderate 1.55 · Very active 1.725 · Extremely active 1.9Fat loss: −500 kcal/day ≈ 0.5 kg/week · Lean bulk: +200–300 kcal/day
Macro Calculator
Daily protein, carbs and fat targets from your calorie goal. Splits by training goal — fat loss, muscle gain, maintenance, keto or endurance.
Fat loss: P 40% / C 35% / F 25% · Muscle gain: P 35% / C 45% / F 20%
Keto: P 30% / C 5% / F 65% · Endurance: P 20% / C 60% / F 20%
Protein target: 1.6–2.2g/kg bodyweight for muscle retention/growth (Stokes et al. 2018).
Calorie Burn Estimator
Calories burned during exercise from body weight, duration and MET (metabolic equivalent). Covers 20+ activities.
Calories = MET × Weight (kg) × Time (hrs)
MET (Metabolic Equivalent of Task) = energy cost relative to rest. Sitting = 1.0 · Walking = 3.5 · Running = 7–12+
Training
3 toolsOne Rep Max (1RM)
Estimated 1RM from any working set. Choose from Epley, Brzycki, Lander or Lombardi formula. Includes full percentage table.
Epley: W × (1 + R/30)
Brzycki: W ÷ (1.0278 − 0.0278 × R)
Training zones: 90–100% 1RM = max strength · 75–85% = hypertrophy · 60–75% = strength-enduranceMost accurate at 3–8 reps. Accuracy drops significantly above 10 reps.
Training Volume Load
Total volume load (sets × reps × weight) for a session or week. Identifies training zone and weekly tonnage for progressive overload tracking.
Volume = Sets × Reps × Weight
Training zones by rep range: 1–5 = strength/neural · 6–12 = hypertrophy · 13–20 = strength-endurance · 20+ = enduranceTrack weekly volume per muscle group — increase by 5–10% each week for progressive overload.
Rest Period Calculator
Optimal rest time between sets based on training goal (strength, hypertrophy, endurance or power) and set intensity.
Hypertrophy: 1–3 min (metabolic stress + muscle damage)
Endurance: 30–90s (maintains elevated HR)
Power: 3–8 min (full neural recovery for maximal output)
Progress & Planning
3 toolsBody Weight Trend
Rate of weight change, estimated calorie surplus or deficit, and whether the pace is appropriate for your goal.
~7700 kcal = 1 kg body weight change
Weigh yourself at the same time each day (morning, post-toilet) for consistent data. Short-term fluctuations of 1–2 kg are normal from water, glycogen and food volume — look at 7–14 day averages.
Target Date Calculator
How long to reach your goal weight at a given rate of change. Shows target date, daily calorie adjustment and sustainability check.
Weeks = Weight difference ÷ Rate per week
Recommended rates: Fat loss: 0.5–1% bodyweight/week · Muscle gain: 0.25–0.5 kg/week (natural)Metabolism adapts over time — recalculate TDEE every 4 weeks and adjust calories accordingly.
Heart Rate Training Zones
5 personalised training zones using Karvonen (heart rate reserve) or % of max HR. Add resting HR for Karvonen method.
Max HR (Tanaka): 208 − (0.7 × Age)
Karvonen target = RHR + (HRR × Zone%)
HRR = Heart Rate Reserve = Max HR − Resting HRZone 2 (60–70% HRR) is the most important for aerobic base and fat metabolism — often neglected in favour of high-intensity work.