Health numbers, from standard formulas.

About these tools

Seven calculators built on the reference equations used in clinical practice — Devine for ideal body weight, Mifflin-St Jeor for metabolic rate, the US Navy method for body fat, and the standard formulas behind BMI, daily water intake, pregnancy due dates and sleep cycles.

Every one of them names the equation it uses, because a health number without its method behind it is worth very little. They are general estimates for healthy adults, not medical advice, and each page says so plainly — anything that matters should be checked with a doctor who can see the whole picture.

Nothing here needs an account, and nothing you put into any of them is uploaded or stored. Every tool is a single page that does one job, so you can bookmark the one you use and skip this page entirely next time.

How to read these numbers

Every one of these calculators carries a “Method, limitations and sources” section on its own page, setting out the exact formula, the inputs it uses, what it assumes, the groups it is least reliable for, and when the result should not be used at all. If a number here surprises you, read that section before acting on it.

Two things worth saying up front. First, these are population formulas: they describe averages across large groups, so an individual result can sit some distance from the average without anything being wrong. Second, no page on this site has been reviewed by a doctor, and none of it is medical advice — the formulas are cited so you can check them, not so the output carries clinical authority. Anything that matters to your health belongs in a conversation with a clinician who can see your full picture.

• CDC — About Body Mass Index
• ACOG Committee Opinion No. 700 — Methods for Estimating the Due Date
• American Heart Association — Target Heart Rates
• Institute of Medicine — Dietary Reference Intakes for Water and Electrolytes
• AASM / SRS consensus — seven or more hours of sleep for adults

What these numbers are, and what they are not

Every calculator in this section applies a published formula to the figures you enter. That is genuinely useful — the formulas come from clinical and research literature and are the same ones used in practice — but a formula is a population-level generalisation, and you are an individual. It has no knowledge of your medical history, medication, body composition, activity or anything a clinician would consider before drawing a conclusion.

The clearest illustration is BMI. It divides weight by height squared and cannot distinguish muscle from fat, which is why it classifies many athletes as overweight and why it performs differently across ethnic groups — several health authorities use lower thresholds for people of South Asian descent for exactly this reason. It works reasonably as a population screening measure and poorly as an individual verdict, and the same caution applies in some form to every calculator here.

Using them sensibly

Treat the outputs as a starting point for a conversation rather than a conclusion. A figure outside a typical range is a reason to ask a question, not a diagnosis; a figure inside one is not a clearance. Estimates such as calorie needs and ideal weight vary by several hundred units and several kilograms respectively depending on which formula is used, which is itself informative — the spread between methods tells you how much precision the number really carries.

None of these tools can identify a condition, and none should be used to decide whether to seek care. Anything persistent, worsening or worrying is a reason to see a doctor regardless of what a calculator returns. Where these pages cite figures, they reference published sources such as the CDC, ACOG and the American Heart Association so you can read the original guidance rather than take a number on trust.

Your information stays on your device

Weight, height, age, cycle dates and every other figure you enter are processed in your browser and never transmitted or stored on a server. Health information is among the most sensitive material anyone puts into a website, and the only reliable protection is for it not to be sent anywhere in the first place.

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