About HealthTools

HealthTools is a free reference site for health and fitness calculations. We build calculators that show their working: the equation that produced your number, the study it came from, the population it was validated on, and the situations where it stops being reliable. Ten calculators are live today, grouped across body composition, nutrition and energy, fitness and training, and women's health.

Who writes this

Titus Jones

Publisher and writer

HealthTools is written and run by one person. Titus Jones is a blogger and publisher: he researches what people actually search for in health and fitness, writes the guides and the calculator copy himself, and earns from the advertising that runs alongside them. That is the entire business model, and it is set out here rather than left for you to guess at.

He is not a doctor, a dietitian, a physiotherapist or a trainer, and nothing here is written in that capacity. What he does bring is the discipline the work requires: every formula on every calculator is traced back to the paper that published it, the population it was validated on is named, and the cases where it stops working are written down next to the result rather than buried. Where a claim cannot be sourced, it does not go up.

Write to jonestitus194@gmail.com, or use the contact form.

The problem we exist to solve

Type "BMI calculator" into a search engine and you will get thousands of results. Almost all of them are black boxes. You enter your height and weight, a number appears, and nothing on the page tells you which formula ran, who published it, which group of people it was derived from, or how wrong it is likely to be for someone like you.

That matters more than it sounds. Body-fat estimates from tape-measure equations carry a typical error of three to four percentage points. Four accepted ideal-weight formulas can disagree by several kilograms for the same person. Maximum heart rate predicted by the old 220 minus age rule differs from the Tanaka equation by a margin wide enough to change which training zone you aim for. A number with no error bar and no citation is not information. It is decoration.

Most health calculators are black boxes. We publish the equation, the population it was validated on, and its known limitations, so you can judge the number for yourself.

What that commits us to

The mission above is only worth something if it constrains what we publish. In practice it means four things, on every calculator, every time:

The equation is printed on the page. Written out in full, in ordinary notation, next to the result. No proprietary scoring systems and no indexes we invented.
The original source is cited. Mifflin-St Jeor for resting metabolic rate, Tanaka for heart-rate maximum, Devine and Robinson for ideal weight, the Compendium of Physical Activities for exercise energy cost, Naegele's rule for obstetric dating. We name the paper, not just the concept.
Limitations are stated upfront. BMI misreads muscular and very tall bodies. Circumference methods are sensitive to how you hold the tape. Where a formula has a known failure mode, it appears on the tool itself, not buried in a footnote.
Disagreement is shown, not hidden. When several validated equations exist and they conflict, we run all of them and show you the spread. The disagreement is the useful part.

Our editorial policy sets out how sources are ranked and how formulas are checked before a calculator ships.

How the calculators work

The calculators run in your browser. When you enter a height, a weight, a waist measurement or a date, that figure is processed by JavaScript on the page and is not sent to our server. Our privacy policy describes what does and does not reach us.

What is in the toolkit

10 calculators are published, organised into the areas below. Each entry lists the tools currently live in that section, and the wellness section is the newest. It stays deliberately thin until we have equations there we can cite and defend.

Body Composition: Fat, lean mass and the ratios that predict health risk.
BMI Calculator · Body Fat Calculator · Ideal Weight Calculator
Nutrition & Energy: Energy needs, macronutrient targets and hydration.
TDEE Calculator · Macro Calculator · Water Intake Calculator
Fitness & Training: Heart rate zones, strength standards and workout output.
Heart Rate Zone Calculator · One-Rep Max Calculator · Calories Burned Calculator
Women's Health: Cycle tracking, ovulation windows and pregnancy dating.
Pregnancy Due Date Calculator
Wellness: Sleep timing, recovery load and daily habit targets.
Still in research, with nothing published yet.

You can browse every calculator in one place, or read the guides, which explain what a result means, when it misleads, and what to do with it. Guides exist because a number on its own rarely answers the question someone actually had.

Who this is for

We write for people who want to understand a health metric rather than simply be handed one: someone starting to train and trying to set a sensible calorie target, someone told their BMI is in a particular band and wanting to know what that does and does not mean, a coach checking which one-rep-max formula is appropriate for higher repetition ranges, a student learning where these equations came from.

What HealthTools is not

Being specific about this matters as much as describing what we do. HealthTools is not a clinic and not a healthcare provider. It is not a diagnostic service. Nothing here can tell you whether you have a condition, and no result should be read as a finding. We do not offer personalised medical advice: we cannot review your numbers, interpret them in the light of your history, or tell you what to do about them, and we will decline if asked. There is no clinician on call, no triage, and no doctor–patient relationship created by using the site. What we publish is a reference work of published equations, implemented transparently and explained honestly. A reference work is not a consultation.

Who this is not for

We should be equally clear about the other side. This site is not a substitute for clinical care, and it is not built for making treatment decisions. If you are managing a diagnosed condition, recovering from or living with an eating disorder, pregnant, calculating for a child or adolescent, or taking medication that affects heart rate or fluid balance, the population averages behind these formulas may not describe you at all. In those situations the right tool is a conversation with a qualified clinician who knows your history. Our medical disclaimer covers this in full, and it is worth reading before you act on anything here.

How the site is funded

HealthTools is free to use and funded by advertising. That is also how Titus Jones earns a living from it, which is worth saying plainly: this is a publishing business, not a hobby, and the guides are researched because they are read.

Ads never influence what we publish, which formulas we choose, or how we describe a study's limitations. Nobody pays for a placement in a guide, and no product is written about in exchange for money. If something is ever recommended, it is because the evidence supports it, and the reasoning will be on the page for you to check.

Corrections and contact

We get things wrong sometimes. If you spot an error in a formula, a misread citation, or a limitation we have failed to mention, please tell us. Corrections of that kind are the most valuable messages we receive, and they are read by the person who wrote the page. Write to jonestitus194@gmail.com or use the contact form. We cannot answer individual medical questions, but we will always engage with a question about a source.

HealthTools is an independent publication and is not affiliated with any of the research groups, professional bodies or clinical organisations whose published equations and guidelines we cite.