Health & Fitness Calculators
BMI, calorie, BMR, body fat, pregnancy and heart rate calculators based on standard medical formulas.
What each health calculator can and cannot tell you
Health numbers are useful as a starting point and dangerous as a verdict. A formula only knows the handful of figures you typed in: it has never seen your blood work, your training history or your family's medical record. Read these outputs as a rough map, then let a doctor or dietitian redraw it.
Weight and body composition
The BMI calculator is the one everyone starts with, and also the one most often misread. BMI is simply weight divided by height squared. It does not distinguish muscle from fat, which is why a lean athlete and someone carrying excess fat can land on the same number. It is a population screening tool that happens to be convenient for individuals, not a diagnosis.
If you want a composition estimate rather than a ratio, the body fat calculator uses tape measurements, and the ideal weight calculator gives a height-based range from the classic clinical formulas. Expect the ranges from different formulas to disagree by several kilograms; that spread is honest information, not an error.
Energy: BMR, TDEE and calories
Three terms get mixed up constantly, so here is the difference in one place:
| Term | What it measures | Use it for |
|---|---|---|
| BMR | Energy your body burns at complete rest, keeping organs running | A floor you should rarely eat below |
| TDEE | BMR plus movement, exercise and digestion over a full day | Your actual maintenance intake |
| Target intake | TDEE adjusted up or down for a goal | Planning a gain or a loss |
So the BMR calculator comes first, the TDEE calculator builds on it, and the calorie calculator turns it into a daily goal. The weak link is the activity multiplier you choose. Almost everyone picks one level too high, which is the single most common reason a calorie plan stalls. If your weight is steady on a given intake, that intake is your real TDEE, whatever the calculator said.
Food and fluid
Once you have a calorie target, the macro calculator splits it into protein, carbohydrate and fat, and the protein calculator gives a gram figure on its own if that is the only number you are tracking. The water intake calculator scales a baseline by body weight and activity. Drinks, fruit and cooked food all count toward it, so the figure is not a glasses-of-water quota.
What none of these capture: medication, thyroid and hormonal conditions, pregnancy, recovery from illness, or how a meal plan fits your actual life. A plan you can follow beats an optimal one you abandon.
Cycle and pregnancy dates
The pregnancy due date calculator counts forward from your last period, the ovulation calculator estimates the fertile window, and the period calculator projects upcoming dates from your usual cycle length. All three assume a reasonably regular cycle. If yours varies by more than a few days, or you are tracking for fertility treatment, a scan gives a date these formulas cannot.
Training
The heart rate calculator turns your age into training zones, and the calories burned calculator estimates the cost of a session from its duration and intensity. Both lean on averages. Measured maximum heart rates differ from the age-based estimate by a wide margin in both directions, and burn estimates for the same workout can differ by a third between two people of the same weight.
One honest line
These tools implement published formulas correctly. They cannot examine you. If a result worries you, or you are managing a condition, pregnant, under eighteen or well outside the typical ranges, take the number to a clinician and let their assessment be the one that counts.
All 14 health tools on CodingMarble Calculator are free, need no sign-up and work on mobile: BMI Calculator, BMR Calculator, Calorie Calculator, TDEE Calculator, Body Fat Calculator, Ideal Weight Calculator, Macro Calculator, Protein Calculator, Water Intake Calculator, Pregnancy Due Date Calculator, Ovulation Calculator, Period Calculator, Heart Rate Calculator, Calories Burned Calculator.
Last reviewed 2026-10-14 · How we check every calculator