Performance Fitness Lab
Stop guessing, start measuring. Whether you're losing weight or chasing a world record, our data-driven tools help you reach your peak performance.
Metabolic Metrics
Understand your chemistry and calorie requirements.
BMI & BMR (2026)
Get your Body Mass Index and Basal Metabolic Rate to understand your daily calorie needs.
TDEE Calculator
How many calories do you actually burn in a day? Find out based on your activity level.
Body Fat %
Estimate your body fat percentage using standard naval or skinfold formulas.
Strength & Intensity
Tools for athletes looking to push their physical limits.
1-Rep Max
Safely calculate your maximum lift strength for any exercise without the risk.
Heart Rate Zones
Optimize your cardio by finding your fat-burning and peak performance heart rate zones.
Pace Calculator
Plan your next run, marathon, or triathlon with precise split and pace calculations.
Understanding Your Body Metrics
Effective fitness starts with measurement. Before setting goals, you need a baseline - and the right metrics depend on your objectives. Weight alone is misleading: a muscular athlete may "weigh too much" by BMI standards but have excellent body composition. That is why we provide multiple measurement tools that paint a complete picture of your fitness.
BMR and TDEE: Your Calorie Foundation
Your Basal Metabolic Rate (BMR) is the number of calories your body burns at complete rest - just to keep organs functioning, blood circulating, and cells repairing. For most people, BMR accounts for 60-75% of total daily calories. Your Total Daily Energy Expenditure (TDEE) multiplies BMR by an activity factor (1.2 for sedentary, up to 1.9 for very active) to estimate actual daily calorie burn. Knowing your TDEE is the foundation for weight loss (eat below it), maintenance (eat at it), or muscle gain (eat above it).
Training with Heart Rate Zones
Heart rate training divides effort into five zones based on your maximum heart rate (estimated as 220 minus your age). Zone 1-2 (50-70% max) burns fat efficiently and builds aerobic endurance. Zone 3 (70-80%) improves cardiovascular fitness. Zone 4-5 (80-100%) develops speed and power but cannot be sustained for long. Our heart rate zone calculator personalizes these ranges for your age and fitness level.
Fitness Lab FAQs
How accurate is the BMI calculator?
BMI is a useful population-level screening tool but has limitations for individuals. It does not distinguish between muscle and fat mass, so athletes may be incorrectly classified as overweight. Pair BMI with body fat percentage and waist circumference for a more complete picture.
What is the best way to lose body fat?
The most effective approach combines a moderate calorie deficit (300-500 calories below TDEE), adequate protein intake (0.7-1g per pound of bodyweight), resistance training to preserve muscle, and consistent sleep (7-9 hours). Crash diets lead to muscle loss and metabolic adaptation - slow and steady wins the race.
How do I know my one-rep max without testing it?
Our 1-rep max calculator uses the Epley formula: 1RM = Weight × (1 + Reps/30). If you can bench press 185 lbs for 8 reps, your estimated 1RM is 185 × (1 + 8/30) = 234 lbs. This is safer than actually attempting a maximal lift without a spotter.
What heart rate zone should I train in?
For fat loss and general fitness, spend most of your time in Zone 2 (60-70% max heart rate) - this is the "fat-burning zone" where your body primarily uses fat for fuel. For performance improvements, mix in Zone 4-5 intervals. A common split is 80% low intensity / 20% high intensity.
Chasing a PR?
Need a specialized calculator for your sport or diet? We're here to help you measure what matters. Suggest a feature via our contact form.
Guides behind the health calculators
The BMR, TDEE, one rep max, heart rate and pace calculators above each run one published equation. The guides below set the main equations side by side for the same inputs, say which populations they were built on and how far a prediction can miss a measured value, so you can tell what the number on the calculator is worth.
- BMR and TDEE equations compared: Mifflin-St Jeor, Harris-Benedict, Katch-McArdle and the 2023 National Academies equations, worked for three people.
- One rep max formulas compared: seven 1RM formulas run on the same set from 1 to 15 reps, and which rep range gives the most reliable estimate.
- Max heart rate formulas compared: 220 minus age, Tanaka, Gellish, Nes and Gulati from age 20 to 80, with Karvonen zones worked for one runner.
- Riegel race time predictor vs the 2016 correction: marathon predictions from 5K, 10K and half-marathon times at 20 to 50 weekly miles, checked against 633 runners' real results.