Health calculators
Estimate BMI, calories, and other everyday health numbers.
Health numbers are indicators, not verdicts. They are useful once you understand what they measure and what they cannot see. The calculators below give you the result and the caveats that belong with it.
Weight and body composition
BMI calculator
Work out your Body Mass Index from your height and weight, in metric or imperial units, and see the WHO weight category.
BMI calculator for children
Work out a child's BMI from weight and height, with age and sex noted because child BMI is read against percentile growth charts.
Body fat calculator
Estimate your body-fat percentage with the US Navy tape method, plus your fat and lean mass and a fitness category.
Historical ideal-weight formula calculator
Compare four historical ideal-body-weight formulas from your height and sex, see their full min–max span, and view a separate BMI reference range.
Waist-to-hip ratio calculator
Work out your waist-to-hip ratio from your waist and hip measurements and see the WHO health-risk category for your sex.
Weight loss calculator
Work out the weekly rate and daily calorie deficit needed to reach a goal weight in a set number of weeks.
GLP-1 weight loss calculator
Project weight loss on a GLP-1 medication from your starting weight and time on treatment, using clinical-trial averages. Informational only.
Calories and nutrition
Calorie calculator
Estimate resting energy, maintenance calories, and a fixed goal adjustment for ages 19–78, with the selected activity factor and adjacent-level sensitivity shown.
BMR calculator
Estimate your basal metabolic rate — the calories your body burns at rest — from your weight, height, age, and sex using the Mifflin-St Jeor equation.
TDEE Calculator: Daily Calories & Maintenance
Calculate how many calories you need each day from your BMR and activity level, including maintenance and simple deficit or surplus scenarios.
Macro calculator
Split a daily calorie target into grams of protein, carbs, and fat using a balanced, low-carb, or high-protein ratio.
Protein intake calculator
Estimate your daily protein in grams from your body weight and goal, with a per-meal split across four meals.
Daily Water Intake Calculator
Estimate how much water you should drink each day based on your body weight and activity level.
Pregnancy and family
Pregnancy due date calculator
Estimate your due date with Naegele's rule from the first day of your last period, plus conception and third-trimester dates.
Ovulation calculator
Estimate your ovulation day and fertile window from the first day of your last period and your average cycle length.
Height calculator
Predict a child's adult height from the parents' heights using the mid-parental method, with a typical range.
Fitness and training
Everyday health
Age Calculator
Find out exactly how old you are in years, months, days, and total days from any date of birth.
Life expectancy calculator
Get a rough life expectancy estimate from your age, sex, and a few lifestyle factors. A simplified illustration, not a forecast.
Sleep calculator
Find the best times to go to bed for a chosen wake-up time, based on 90-minute sleep cycles, so you wake at the end of a cycle.
BAC calculator
Estimate blood alcohol concentration with the Widmark formula from standard drinks, body weight, sex, and time. An estimate only — never drink and drive.
Carbon footprint calculator
Estimate your yearly carbon footprint from driving, flights, electricity, and diet — with a monthly figure and trees needed to offset it.
Body measures tell you something, not everything
BMI relates weight to height and places the result in the WHO categories. It is a useful screening tool at population level, but it cannot distinguish muscle from fat and takes no account of where fat sits. A muscular person can land in the overweight band without a weight problem, and two people with the same BMI can carry very different risk.
BMI calculator gives the number and the category, BMI calculator for children uses percentiles instead, because a child's BMI has to be read against age and sex, and Waist-to-hip ratio calculator and Body fat calculator add what BMI cannot see: distribution.
Energy: from resting rate to daily need
The three energy calculators form a chain. BMR is what the body uses at rest. TDEE multiplies BMR by an activity level to give total daily expenditure. The calorie calculator adds a goal on top — maintain, lose, or gain. The big uncertainty is the activity level: people overestimate it systematically, and one step too high inflates the whole result.
BMR calculator is the starting point, TDEE calculator adds activity, and Calorie calculator turns it into a daily target. Macro calculator splits those calories across protein, carbohydrate, and fat, and Protein intake calculator handles protein on its own.
Weight and targets
Weight loss calculator works out the timeline for a goal from a calorie deficit, Ideal weight calculator gives a range rather than one figure because the formulas disagree, and GLP-1 weight loss calculator estimates from published trial averages. That last one is worth reading the caveats on: it describes a study average, not what you will experience, and medication decisions belong with a doctor.
Pregnancy, sleep, and everyday life
Pregnancy due date calculator and Ovulation calculator work on cycles and dates. Sleep calculator counts backwards from a wake time in sleep cycles, and Daily water intake calculator gives a starting point from weight and activity.
What these calculators do not do
They do not diagnose, do not replace an examination, and know nothing about your medical history, medication, or family risk. Every formula here is a population average, and an average describes no individual precisely. If you are worried about your weight, your metabolism, a pregnancy, or a symptom, that is a question for a doctor and not for a calculator.
FAQ
- Is BMI reliable?
- As population-level screening it is useful and well established. On an individual it is blunt: it does not separate muscle from fat, ignores where fat sits, and fits poorly for very muscular, very tall, very short, pregnant, and older people. Treat it as one signal among several.
- Why does children's BMI use percentiles?
- Because body composition changes throughout childhood. A BMI that is normal for a five-year-old means something different at thirteen. The percentile compares the child with peers of the same age and sex rather than against an adult scale.
- Which activity level should I pick for TDEE?
- A lower one than you first think. Most people overestimate their activity, and one step too high inflates the whole daily figure. Start conservative, track weight over a few weeks, and adjust to what actually happens.
- Why does the ideal weight calculator give a range?
- Because several established formulas exist and they disagree. A range represents that uncertainty more honestly than a single number that looks precise. Body composition, frame, and health matter more than any formula can capture anyway.
- Can I rely on the GLP-1 calculator?
- It shows an estimate based on published trial averages, not a prediction for you. Real weight loss varies considerably between people and depends on dose, duration, diet, activity, and side effects. Decisions about medication are made with a doctor.
- Is the blood alcohol calculator accurate enough to judge driving?
- No, and it should never be used that way. Alcohol absorption and clearance vary with food, medication, sex, weight, liver function, and other factors no formula captures. If you are driving, an estimate is not the answer.