Numbers for your body, explained plainly
A calculator can't diagnose anything. What it can do is turn vague questions into numbers you can track. How many calories do I burn in a day? How much water should I drink? Where does my running pace put me at a 10K?
The tools on this page cover body composition, energy, training and recovery. They run in your browser, they don't ask for an account, and your measurements stay on your device. That's worth having for health data.
Body composition and weight
BMI divides weight by height squared and places you in one of the standard WHO categories. It's quick and it's crude. It can't tell muscle from fat, so a lean, muscular person can land in the overweight range. Use it as a rough screen, not a verdict.
Body fat tools give a better picture. The Navy method uses tape measurements of your neck, waist and, for women, hips. Results come with fitness classifications and a split between lean mass and fat mass. Expect an error of a few percentage points compared with a DEXA scan.
The ideal weight calculator compares four older formulas (Hamwi, Devine, Robinson and Miller). They disagree with each other by several pounds, which is a good reminder that "ideal" is a range, not a target.
Calories, macros and metabolism
BMR is the energy your body burns at rest. TDEE multiplies that by your activity level to estimate what you burn in a normal day. The BMR and TDEE calculator shows three formulas side by side: Mifflin-St Jeor, Harris-Benedict and Katch-McArdle. If you know your body fat, Katch-McArdle is often the most accurate.
The calorie calculator turns that into targets for losing, maintaining or gaining weight. The macronutrient calculator splits those calories into protein, carbohydrates and fat.
A realistic cut is around 300 to 500 calories under maintenance. Bigger deficits tend to cost you muscle and energy, and they're hard to keep up.
- Weigh yourself at the same time of day and average the week
- Recalculate after every 10 pounds lost or gained
- Treat results as a starting point and adjust from real progress
Training and performance
The one rep max calculator estimates your max lift from a lighter set using the Epley, Brzycki, Lander, Lombardi and O'Connor formulas. It gives an average and a table from 50 to 100 percent. Estimates get shakier above ten reps, so use a heavy set of three to five.
The running pace calculator solves for pace, time or distance and includes race presets, splits and Riegel projections. The VO2 max estimator offers three methods, including a 1.5 mile run and a step test, and rates you by age and sex.
Don't test your max when you're tired or injured. Warm up properly and have a spotter for heavy lifts.
Sleep, hydration and pregnancy
The sleep cycle calculator works backward from your wake time. Sleep runs in cycles of about 90 minutes, and waking at the end of one tends to feel better than waking in the middle. It allows for the time it takes you to fall asleep.
The hydration calculator starts with 35 ml per kilogram of body weight and adjusts for activity, climate, pregnancy and altitude. It's a guide. Thirst, urine color and your doctor's advice matter more than any formula.
The pregnancy due date calculator estimates a date from your last period, conception date or an ultrasound, and shows a milestone timeline. Only about 5 percent of babies arrive on the due date, so treat it as the middle of a window.
When to see a professional
If a result worries you, talk to a doctor. Unexplained weight changes, chest pain, dizziness during exercise or any pregnancy concern all need a real clinician, not a web page.
These tools are for education and planning. They aren't medical advice, and no calculator knows your history, your medications or your genetics.
Using the tools without obsessing
Numbers are useful for spotting trends and starting a conversation. They're poor at telling you how you feel. A BMI of 26 doesn't mean much if you lift heavy and sleep well. A BMI of 22 doesn't guarantee fitness if you never move.
Pick one or two measures and track them over weeks, not days. Weight, waist, resting heart rate, sleep hours or how a regular run feels all work. Changing what you measure every week just creates noise.
A realistic week of changes
Let's say your maintenance calories come out at 2,300. You don't need a radical cut. A 300 calorie dip, a daily walk and a bit more protein can shift weight slowly without making you miserable. Half a pound a week sounds dull, but it adds up to a stone in a few months.
The same logic applies when you want to gain. Add 200 to 300 calories, lift three times a week and eat protein at each meal. Fast bulks mostly add fat.
Check progress every two weeks. If nothing moves, change one thing, not five.
- Adjust calories by small steps of 100 to 200.
- Keep protein steady while you change the rest.
- Weigh at the same time under the same conditions.
- Give any change at least two weeks before judging it.
Water, sleep and the boring basics
Most people need more sleep than they get. Seven to nine hours is the common guidance for adults, and the sleep calculator helps you pick a bedtime that matches whole sleep cycles of about 90 minutes. Waking mid-cycle is why you can feel worse after eight hours than after seven and a half.
Hydration needs vary with weight, heat and activity. Pale yellow urine is a simple, free check. Don't force huge amounts; more isn't better past a point.
These aren't glamorous, but they affect energy, mood and training more than most supplements.
Limits of any online calculator
These tools use standard formulas that work on averages. You're not an average. Medical conditions, medication, age, pregnancy and a history of eating problems all change what's appropriate. If something feels off, or the output worries you, talk to a doctor or registered dietitian. Your inputs stay in your browser and aren't stored.