Health Calculators

Health numbers are the kind you actually act on — what to eat today, how much water to drink, whether a new symptom is worth a call to your doctor. The health calculators on this page turn a handful of basic body measurements into plain, personal figures you can use right away. None of them diagnose a condition or replace a clinician; they give you a starting point and a consistent way to track changes over time.

The Calorie Calculator and the BMR (basal metabolic rate) Calculator both use the Mifflin–St Jeor equation, the method most often recommended for everyday estimates because it tends to be more accurate than older formulas. Your BMR is the number of calories your body burns at complete rest — simply keeping you alive, with no deliberate movement. Layer your activity level on top and you get your TDEE (total daily energy expenditure), the figure that tells you how many calories to eat to hold your weight steady, or to lose or gain gradually. Use the two calculators together rather than in isolation. Set a daily target with the Calorie Calculator, then check the BMR Calculator to see the floor below which you should not drop. Eating consistently under your BMR can slow your metabolism and make long-term weight control harder, so treat the BMR as a guardrail rather than a goal. A safe, sustainable deficit is usually a few hundred calories a day, not a drastic cut. The Water Intake Calculator estimates daily fluid needs from your body weight and how much you move, with an adjustment for hot weather. It is a guide, not a rule — thirst, kidney health, and some medications all shift the real number, and a meaningful share of your water comes from food. A practical habit is to front-load fluids earlier in the day so you are not drinking large amounts right before bed, which can disrupt sleep. The Due Date Calculator works from your last menstrual period using Naegele's rule — adding 40 weeks, adjusted for an irregular cycle length — and also estimates conception and the start and end of each trimester. These dates are estimates, not certainties; only an early ultrasound gives a precise gestational age, and most babies arrive within a two-week window on either side of the calculated date. The Body Fat Calculator uses the U.S. Navy circumference method, which estimates body fat percentage from a few tape measurements at the waist, neck, and (for women) hips. It is less precise than a DEXA scan or hydrostatic weighing, but it is free, private, and repeatable at home, which makes it useful for spotting trends over weeks and months rather than a single definitive reading. Pair it with your weight and waist measurement instead of treating the percentage in isolation, since hydration and recent meals can shift the result by a point or two.

Every tool here runs entirely in your browser, keeps your inputs on your device, and needs no account. If you normally think in imperial units, convert before you enter numbers — most inputs expect metric (centimeters and kilograms). Re-measure under the same conditions each time, using the same scale and the same time of day, so the figures you compare are genuinely comparable. Treat the results as a baseline for habits and conversations, then bring anything that worries you to a qualified health professional.