Health numbers you can actually check.
Most calculators hand you a number and hide the maths. HealthTools shows you the equation, the population it was validated on, and where it breaks down, so you can judge the result instead of trusting it blindly.
What you'll find here
- 10 calculators, metric or imperial
- 51 guides that explain the result
- Every answer names the study behind it
The equation is on the page
Every result shows the formula that produced it, written out in full. No proprietary scoring, no invented indexes.
Sourced to the original paper
Mifflin-St Jeor, Tanaka, Devine, the Compendium of Physical Activities. Each calculator cites the study it came from.
Limitations stated upfront
BMI misreads muscular bodies. Circumference methods carry ±3–4% error. We say so on the tool itself, not in fine print.
Every calculator, grouped by what you're trying to learn
Pick the question you actually have. Every tool works in metric or imperial, and shows the equation behind its answer.
Body Composition
Fat, lean mass and the ratios that predict health risk.
Nutrition & Energy
Energy needs, macronutrient targets and hydration.
Fitness & Training
Heart rate zones, strength standards and workout output.
Women's Health
Cycle tracking, ovulation windows and pregnancy dating.
When two equations disagree, we show you both
Four published medical formulas can look at the same person and give four different ideal weights. For a 190 cm man, one of them says 84 kg and another says 77 kg. All four are in normal clinical use, so quietly picking one and dropping the rest would mean making that call for you. Our calculators run all of them and show you the spread.
Drag the height below. Each dot is one of those four formulas answering the same question, and the shaded band is the distance between the highest and lowest answer.
Read our editorial policyBelow 5 ft none of these four equations is defined. Each falls back to its base constant, which is why the dots stop moving.
Gap between highest and lowest 3.3 kg
The reasoning behind the numbers
A calculator gives you a figure. These explain what it means, when it misleads, and what to do next.
When a Health Number Warrants a Doctor's Visit
Calculators are screening prompts, not diagnoses. Here are the categories of result that deserve a professional opinion, and how to make that appointment useful.
Strength Training for Beginners: The First Twelve Weeks
Beginners adapt to almost anything, so the programme matters less than showing up. Here is what to do for twelve weeks, what to ignore, and why less is more at the start.
Carbohydrates and Fibre: Setting an Intake That Fits Your Training
Carbohydrate has no minimum requirement but it fuels hard work, so the right intake follows your training volume rather than any fixed percentage of calories.
Start with the number you came for
Ten calculators, each one showing the equation it used and where that equation stops working.
Open the toolkit