Health & Fitness Calculators

What the health calculators cover

Health numbers have a bad habit of arriving without their working: an app announces your daily calories, a chart declares your BMI category, a wearable states your zones, and none of them says where the figure came from. Every calculator on this shelf takes the opposite approach. Each one names the published formula it uses, shows your numbers substituted into it, and is plain about what the result can and cannot tell you.

The shelf is organised into six topics. Calories & Nutrition works out what you burn and what to eat. Calories in Food & Drink tells you what is actually on the plate. Exercise & Training handles pace, burn and gym numbers. Body & Weight covers BMI, body fat and healthy ranges. Pregnancy & Fertility tracks due dates and cycles. And Medical holds the clinical formulas, stated plainly and sourced.

Calories: from what you burn to what you eat

The largest topic on the shelf, Calories & Nutrition, follows one chain of reasoning from start to finish. The BMR Calculator establishes your resting burn from three published equations, led by Mifflin-St Jeor; the Daily Calorie Calculator scales it up to a full day's expenditure; the Calorie Deficit Calculator turns a goal weight into a daily target, a finish date and a week-by-week chart, flagged safe or not; and the Macro Calculator splits the target into grams of protein, carbohydrate and fat. Around those four flagships sit the specialists: a Protein Calculator with the research bands per kilogram, a Maintenance Calorie Calculator for holding steady, and generators that turn a number into an actual day of meals.

Its sibling topic, Calories in Food & Drink, answers the question that follows: what is in the food itself. The Food Calorie Checker covers 199 common foods per 100 g and per serving; the Chicken Breast Calorie Calculator settles the raw-versus-cooked weight trap; the Chipotle Calorie Calculator builds a takeaway order from the chain's own published data; and the Recipe Calorie Converter gives home cooking a real per-serving number.

Training numbers that transfer

The Exercise & Training topic is built around numbers you can actually train with. The Pace Calculator solves pace, time or distance for a run from the other two, in kilometres or miles, with a race-day projection. The Target Heart Rate Calculator estimates your maximum from the Fox or Tanaka formulas and lays out the five training zones in beats per minute. The One Rep Max Calculator estimates your single-rep strength from any set, with four proven formulas compared and training percentages ready to use.

The rest of the topic deals in calorie burn, honestly. The Calorie Burn Calculator uses standard MET values and shows gross and net burn side by side, a distinction most apps skip. The Assault Bike Calorie Chart and Rowing Calorie Chart put the machine's own calorie figure next to a physiological estimate and explain the gap between them, and the CrossFit Calorie Converter translates calories, watts and split pace between Concept2 rowing and Assault or Echo bikes, so a score on one machine means something on another.

Body measurements, with their limits stated

The Body & Weight topic starts where most people do, with the BMI Calculator, which gives your body mass index on the standard scale and the healthy weight range for your height, alongside honest notes on what BMI misses. From there the tools get more specific. The Body Fat Calculator estimates body fat percentage from neck, waist and height measurements using the US Navy method; the Army Body Fat Calculator applies the one-site formula the US Army adopted in June 2023 and checks it against your age-and-sex standard; and the Lean Body Mass Calculator compares the Boer, James and Hume formulas side by side.

For the "what should I weigh" question, the Ideal Weight Calculator lines up four classic formulas, Devine, Robinson, Miller and Hamwi, while the Healthy Weight Calculator and Overweight Calculator read BMI and waist measurements together into one plain verdict, which is fairer than either number alone. The Body Type Calculator rounds out the topic with a transparent frame-size and body-type estimate that never pretends a single label settles anything.

Pregnancy, cycles and fertility

The Pregnancy & Fertility topic covers the timeline questions. Before pregnancy, the Ovulation Calculator estimates your fertile window from your last period and cycle length with a six-cycle look-ahead, and the Period Calculator projects when the next periods will start and finish. Once a pregnancy is under way, the Due Date Calculator estimates the due date from your last period, a conception date or an IVF transfer, the Pregnancy Calculator tells you how far along you are today with a verified milestone timeline across the 40 weeks, and the Pregnancy Weight Gain Calculator shows your recommended gain range from the IOM guidance, banded by pre-pregnancy BMI. Looking backwards instead, the Conception Calculator estimates when conception most likely happened from a due date or birth date.

The clinical formulas, in plain words

The Medical topic is small and deliberate: three clinical formulas, each named and sourced. The GFR Calculator estimates kidney function from a creatinine result using the CKD-EPI 2021 equation and shows the corresponding CKD stage. The Body Surface Area Calculator works by the Mosteller formula with Du Bois and others compared alongside. The BAC Calculator estimates blood alcohol concentration from the Widmark formula, with a decline chart and a permanent reminder that the only safe level for driving is zero. All three, like everything on this shelf, are estimators for understanding, not a substitute for a clinician; anything that worries you belongs in front of a doctor, not a web page.

Working one real problem across the shelf

The topics are separated for browsing, but real questions cut across them. Someone starting a weight loss plan might begin with the BMI Calculator to see where they stand, use the Daily Calorie Calculator to find their maintenance number, set a pace with the Calorie Deficit Calculator, pin down protein with the Protein Calculator, plan meals against the Food Calorie Checker, and credit workouts through the Calorie Burn Calculator. Six tools, three topics, one coherent plan, and because every calculator here is free, the whole chain costs nothing to run and nothing to re-run when the weigh-ins start coming back.

Frequently asked questions

Where should I start on this shelf?

With the question you actually have. Weight questions start at the BMI Calculator, eating questions at the Daily Calorie Calculator, training questions at the Pace Calculator or Target Heart Rate Calculator, and pregnancy questions at the Due Date Calculator. Each tool links onward to its natural companions.

Are these calculators medical advice?

No. They implement published formulas and guidance accurately and say so on each page, but a formula built from population averages cannot examine you. Use them to understand your numbers and to have a better-informed conversation with a professional, not in place of one.

Why do different calculators give different answers to the same question?

Because the published formulas genuinely disagree. Four ideal-weight formulas give four figures; three lean-mass formulas give three. Where that happens, these tools show the alternatives side by side rather than hiding the disagreement, because the spread between them is honest information about how precise the estimate really is.

Do the calculators work in metric and imperial?

Yes. Kilograms or pounds, centimetres or feet and inches, kilometres or miles; every tool takes the units you think in and states its results in both where that helps.