Health & Fitness
Ten calculators that turn a few body measurements into the numbers people plan around: weight status, maintenance calories, macro targets, body fat, hydration, cycle dates and running pace. Each is a population-level estimate from a published formula, and none of it is a substitute for a clinician.
BMI Calculator
Calculate your Body Mass Index and see your weight category instantly.
Private · in-browserBMR & Calorie (TDEE) Calculator
Find your basal metabolic rate and daily calorie needs (TDEE) by activity level.
Private · in-browserBody Fat Percentage Calculator
Estimate body fat percentage using the US Navy method.
Private · in-browserIdeal Weight Calculator
Estimate your ideal body weight for your height.
Private · in-browserMacro Calculator
Split your daily calories into protein, carbs and fat grams.
Private · in-browserWater Intake Calculator
Estimate how much water to drink daily based on your weight and exercise.
Private · in-browserPregnancy Due Date Calculator
Estimate your due date from your last menstrual period (Naegele’s rule).
Private · in-browserOvulation & Fertility Calculator
Estimate your ovulation date and fertile window from your cycle.
Private · in-browserRunning Pace Calculator
Calculate your pace per km and speed from distance and time.
Private · in-browserCalories Burned Calculator
Estimate calories burned for an activity from its MET value, your weight and duration.
Private · in-browserWhich calculator do I need?
- Body composition — BMI is a two-input screen from height and weight and nothing more. The body fat calculator uses the US Navy tape method and tells you considerably more if you train, while ideal weight applies the Devine formula, which originated in clinical drug dosing rather than in dieting.
- Energy — the BMR and TDEE calculator uses the Mifflin-St Jeor equation and an activity factor to estimate your maintenance intake. Feed that number into the macro calculator to split it into protein, carbohydrate and fat grams, and use calories burned to price a specific session from its MET value, your weight and its duration.
- Hydration — water intake scales with body weight and adds an allowance for exercise, which is more personal than the eight-glasses rule.
- Cycle and pregnancy — ovulation and fertile window estimates ovulation about 14 days before the next expected period, and the due date calculator applies Naegele’s rule, adding 280 days to the first day of the last period.
- Training — the running pace calculator converts between distance, time, pace per kilometer and speed.
How to read an estimate
Each of these formulas was fitted to a population, so it describes an average person of your height, weight, age and sex rather than you specifically. BMI cannot distinguish muscle from fat, which is why heavily trained people land in the overweight band while carrying little body fat — the limits of BMI covers that in full. Tape-measure body fat depends on measuring the same way every time, so watch the trend rather than one reading.
Calorie numbers are starting points, not targets handed down. Metabolic rate varies by several percent between people with identical inputs, and most people overestimate their activity level. Eat at the estimate for two or three weeks, track weight, and adjust from what actually happened; TDEE and calorie targets explains how to run that loop.
General guidance, not medical advice
Nothing here diagnoses, treats or replaces professional care. The formulas are validated for healthy adults, so they should not be applied to children, and pregnancy, an eating disorder, diabetes, kidney or heart conditions and prescribed medication all change what is appropriate. The cycle tools estimate dates from averages and are not a contraceptive method. If a number worries you or a decision matters, talk to a doctor or a registered dietitian.
Frequently asked questions
- Is BMI reliable if I lift weights?
- Not really. Muscle is denser than fat, so strength-trained people often read as overweight while carrying a low body fat percentage. The height-and-weight formula has no way to tell the two apart. If you train seriously, the tape-based body fat estimate is a far more informative number to track.
- Which calorie number should I actually eat?
- Start at your TDEE, which is your maintenance level — eat roughly that and weight should hold steady. For fat loss subtract a modest amount rather than a dramatic one, and for gaining add a small surplus. Then let three weeks of real weight data tell you whether the estimate was right for you.
- How accurate is the tape-measure body fat estimate?
- Taken carefully it usually lands within a few percentage points of lab methods such as DEXA. Accuracy depends almost entirely on technique: keep the tape level and snug without compressing skin, measure at the same time of day, and stand relaxed. Its real strength is tracking change over weeks, not the single figure.
- Can I use the ovulation calculator to avoid pregnancy?
- No. It estimates a fertile window from cycle averages, and ovulation timing shifts with stress, illness and cycle irregularity, so the window it draws can be wrong by days. It is intended to help with conception timing. For contraception, use a method with a known failure rate and discuss options with a clinician.
- Do these calculators work for children?
- No. Adult BMI cutoffs, the Mifflin-St Jeor equation and the Devine formula are all built for adults. Children and teenagers are assessed against age- and sex-specific growth percentiles instead, which a pediatrician plots over time. Do not read an adult category off these tools for a child.