Health Calculators

Evidence-based tools for body composition, calories, fitness, sleep, and pregnancy. 16 calculators, no logins, no tracking, no diet plans to sell you.

Personal health decisions depend on your own numbers, not somebody else’s. Your BMR is not your neighbor’s. Your target heart rate zones are not your gym buddy’s. The standard formulas (Harris-Benedict, Mifflin-St Jeor, Karvonen, Naegele, IOM weight gain) are well-understood and work just as well in a private browser window as they do in a $200 fitness app.

Every tool below uses those published formulas. Nothing stores your entries. Nothing follows you around afterward.

Body composition and baseline

Start here. BMI is the quick screening number, but body fat percentage, ideal weight, and BMR tell you much more about what your body actually needs day to day. These four tools together give you a complete picture of where you are before you change anything.

BMI Calculator — standard screening number with category interpretation
Body Fat Calculator — US Navy method using simple tape measurements
Ideal Weight Calculator — Devine, Robinson, Miller, and Hamwi formulas compared
BMR Calculator — Mifflin-St Jeor basal metabolic rate, the foundation for calorie math

Calories and nutrition

Fat loss, maintenance, and muscle gain all come down to the same equation: how many calories you need vs how many you take in. These tools handle both sides of that equation, plus the macronutrient split that determines whether the weight you lose comes from fat or muscle.

Calorie & TDEE Calculator — total daily energy expenditure with activity level
Calorie Deficit Calculator — the gap between intake and TDEE for any weight-loss target
Calories Burned Calculator — energy output by activity, duration, and body weight
Macro Calculator — protein, carb, and fat targets for your goal

Fitness and performance

Training smarter beats training harder. Knowing your heart rate zones turns “hard workout” into a specific training stimulus. Knowing your pace turns “faster” into a number you can chase. Hydration and age are the boring fundamentals that hold everything else up.

Water Intake Calculator — daily fluid needs by weight, activity, and climate
Running Pace Calculator — mile and kilometer splits, finish times, and pace charts
Heart Rate Zone Calculator — training zones using Karvonen reserve method
Age Calculator — exact age in years, months, and days

Sleep, pregnancy, and wellness

The calculators in this card are the ones that tend to get asked about in search at 11pm, when somebody has a specific question and wants a specific answer. Sleep cycle timing, due dates, recommended weight gain, and cycle tracking are all standard formulas with straightforward outputs.

Sleep Calculator — optimal bedtimes and wake times based on 90-minute sleep cycles
Pregnancy Due Date Calculator — Naegele’s rule from LMP, conception, or ultrasound
Pregnancy Weight Gain Calculator — IOM 2009 recommendations by pre-pregnancy BMI
Ovulation Calculator — fertile window and next-cycle projections