Hi, I'm Aftab.

I'm Aftab — an AI engineer, a fitness coach with six years of experience, and a self-taught fitness enthusiast. I built this calculator as a hobby project to pull all three of those threads together. I was tired of the BMI tools I kept landing on that wanted my email, blocked the result behind a signup wall, or asked me to "calculate my ideal weight" in exchange for a coaching upsell — so I built the one I wanted to use myself, and open it up to anyone who wants the same.

This page is a transparent look at who runs the site, the clinical professionals who review the content, how the math is sourced and verified, what the calculator can and cannot do, and how to reach me.

Who I am

I'm an AI engineer by profession — I build machine-learning systems for a living — and a fitness coach by calling. I've spent six years coaching people in person and online: programming resistance training, planning calorie and macronutrient targets, and helping people interpret the numbers their watches and scales spit out. I came to fitness the way most self-taught people do — years of learning in the gym, on myself, then on friends, then on paying clients — and the deeper I went, the more I realised how much bad information was circulating online dressed up as science. This site is my answer to that.

I built my first website in my early twenties, taught myself JavaScript and Astro, and have been building small tools ever since. The BMI calculator was the project that pulled all three halves of my life together — I was answering BMI questions for clients every week, I was building AI systems that worked with health data, and I wanted a single place I could send people that was honest, fast, ad-light, and didn't try to sell them anything. This site is that place.

I am not a medical professional. I don't diagnose, I don't prescribe, and I don't treat. The calculator is a screen, not a diagnosis. If the number prompts a change to your diet, medication, or training, please talk to your doctor or a registered clinician first.

How the calculator got built

The first version of the calculator was a single Astro page with a form and a results card. It worked, but it was thin — it answered "what is my BMI" and stopped. As the site grew, I added the body-fat estimate (Deurenberg, 1991), the calorie target (Mifflin–St Jeor, 1990), the lean body mass (Boer, 1984), and the ideal-weight range (Devine, Robinson, Miller). Each formula is documented on its own page with a link to the original paper.

The hardest piece was the child calculator. The CDC publishes its BMI-for-age percentiles as a 438-row "LMS parameters" spreadsheet — every month of age from 2 to 20, separately for boys and girls. Most consumer calculators skip the table and approximate with four coarse bands (underweight, healthy, overweight, obese). I didn't want to do that, so I wrote a small build script that converts the official CSV into a bundled data module, and the calculator now returns the exact percentile using the same Box–Cox LMS formula the CDC's own SAS macro uses. A 10-year-old at BMI 22.96 comes out at the 96.2nd percentile, not "Likely overweight" — which is the right number, not the easy one.

The whole thing runs in your browser. There is no server, no database, and no analytics. Your weight never leaves the device. I chose that architecture on purpose — health data is the kind of information I don't want to be responsible for storing, and I don't want anyone to have to trust me to store it well.

Editorial standards

Every long-form page on this site is written by me and reviewed against the same five checks before I publish it:

1. Primary sources only. Numbers and cut-offs are cited to the original publication — WHO Technical Report Series, the CDC's growth chart release, peer-reviewed journals. No "according to a study" hand-waves.
2. No fake reviews. You will never see a five-star "Aarav M." quote on a calculator page. Reviews on this site are stored in your own browser; you see only the ones you or someone using your device left.
3. No medical claims. The text describes what the literature says. It does not tell you what to eat, how to train, or whether to change a medication. That decision is between you and a qualified clinician.
4. Transparent disclosure. My credentials are listed on every page that has my byline. I am a fitness coach and a developer, not a doctor. If a future article cites medical literature, I will get it reviewed by a clinician before publishing it and the reviewer will be named.
5. Updates over perfection. If a cut-off changes (for example, the 2023 AMA position on BMI) I update the page and date the change. I do not let stale content sit because rewriting it is annoying.

Clinical review network

Because the content here touches health, I do not publish it alone. Every long-form article on the site is reviewed by a certified professional whose area of practice matches the topic before it goes live. A physiotherapist with twenty years of musculoskeletal experience reviews the article on body composition for athletes. A registered dietitian reviews the article on calorie and macronutrient planning. Each reviewer's name, credential and public profile is listed on the Clinical Review Network page so you can see exactly who signed off on what, and contact them directly for a consultation.

The reviewers are paid a flat fee per review. They are not paid per article view, not paid for traffic, and not paid to keep the calculator's results favourable. They have no commercial relationship with the site other than the review itself. If a reviewer ever disagrees with a claim I've made, the article is updated and the change is logged — I would rather publish a shorter, more correct article than a longer, less correct one.

What I cannot do

• I cannot give you medical advice. The calculator is a population-level screen. It does not know your medical history, your medications, your training load, or your pregnancy status. For any of that, please see a clinician.
• I cannot promise the calculator is the best one for you. Other tools — DEXA, hydrostatic weighing, multi-frequency BIA, waist-to-height ratio — give a fuller picture for athletes, older adults, and people on body-recomposition programs. See BMI vs body-fat percentage for the honest comparison.
• I cannot respond to every message instantly. I read everything that comes in through the contact form and reply within a few business days. If your message is time-sensitive, mark it "Press or partnership" and include a deadline.

Get in touch

The fastest way to reach me is the contact form. If you'd rather email, write to codemindsx@gmail.com. Bug reports, clinical-sourcing corrections, and accessibility feedback are especially welcome.

You can also follow the calculator's source code on GitHub at github.com/CodeMindsX-max. I am working on open-sourcing the calculator widget itself under an MIT license; once it is public, the link in the calculator footer will point straight at the repo.

About BMI itself

Body Mass Index is a one-number summary of how heavy you are relative to how tall you are. It is the most widely used population-level indicator of weight status in the world. Knowing where it came from — and what it cannot do — lets you use it well.

The BMI formula

BMI is weight in kilograms divided by the square of height in metres:

BMI = weight (kg) / height (m)²

In imperial units the same number falls out of:

BMI = 703 × weight (lb) / height (in)²

For a 70-kilogram person who is 1.75 m tall, BMI is 70 / (1.75 × 1.75) = 22.86 — comfortably inside the WHO healthy band.

Where the formula came from

The formula was published in 1832 by the Belgian astronomer, mathematician and sociologist Adolphe Quetelet, who called it the "Quetelet Index." It was a population-statistics tool, not a clinical one. The label "Body Mass Index" was coined in 1972 by the American physiologist Ancel Keys, who showed in a multi-country study that weight / height² correlated better with body fatness than several rival indices and was simple to compute. The World Health Organization adopted it as the international screening tool for adult underweight and obesity in 1995, with the cut-offs we still use today.

How adults are classified

The WHO bands for non-pregnant adults age 20 and over are:

• Underweight: BMI < 18.5
• Normal weight: 18.5 ≤ BMI < 25
• Overweight: 25 ≤ BMI < 30
• Obesity class I: 30 ≤ BMI < 35
• Obesity class II: 35 ≤ BMI < 40
• Obesity class III: BMI ≥ 40

The exact same numeric cut-offs apply to males and females — BMI is sex-neutral as a calculation. Body composition at a given BMI does differ by sex, which is one of BMI's well-known limitations.

Why children are different

Children and adolescents are still growing. A BMI of 19 means something very different at age 6 (high) than at age 18 (low normal). The CDC therefore interprets BMI for ages 2–19 as a percentile against same-age, same-sex peers from the 2000 CDC growth reference cohort. The four bands are:

• Underweight: < 5th percentile
• Healthy weight: 5th – < 85th percentile
• Overweight: 85th – < 95th percentile
• Obesity: ≥ 95th percentile (with severe obesity defined as ≥ 120% of the 95th)

To map a child's BMI to a percentile precisely you need the CDC LMS lookup table (which encodes the percentile distribution at every month of age, separately for boys and girls). Our calculator uses the same LMS table, so the percentile you see in the results card is the exact one — not a coarse approximation. The full derivation is on the BMI formula page.

The Asian-cohort adjustment

The WHO Expert Consultation in 2002 (published in The Lancet in 2004) reviewed evidence that, for many Asian populations, the risk of type 2 diabetes and cardiovascular disease starts climbing at lower BMIs than for European-descended cohorts. The consultation declined to define a new global cut-off but recommended that public-health bodies serving Asian populations consider lower "public-health action points" — commonly BMI ≥ 23 for overweight and ≥ 27.5 for obesity. Many Asian countries (notably India, China, Japan and Singapore) now use such adjusted cut-offs in clinical guidelines. Our Charts page shows both columns side by side, and the calculator exposes an "Asian cut-offs" toggle.

What BMI cannot tell you

BMI uses only height and weight. It does not measure:

• Body composition. Two people at BMI 25 can have very different fat-to-muscle ratios. A heavily muscled rugby player and a sedentary office worker can carry the same BMI with wildly different metabolic profiles.
• Fat distribution. Visceral fat (around the organs) carries more cardiovascular risk than subcutaneous fat. Waist circumference and waist-to-hip ratio measure this; BMI does not.
• Bone density and frame size. Older adults often lose bone and muscle ("sarcopenia") while gaining fat, holding BMI roughly constant.
• Pregnancy or recent weight change. BMI is not validated in pregnancy; the pre-pregnancy value is what guides obstetric care.
• Ethnic differences in body composition. See the Asian-cohort note above.

Better tools when BMI isn't enough

For a richer picture of cardiometabolic risk, BMI is usually paired with one or more of:

• Waist circumference — > 102 cm (40 in) for men or > 88 cm (35 in) for women is considered elevated risk in WHO/NIH guidance.
• Waist-to-height ratio — keeping it under 0.5 is a popular rule of thumb.
• Body-fat percentage by DEXA, bio-impedance or skinfold. Our calculator offers the Deurenberg estimate as a rough indicator only.
• Fasting glucose, lipids and blood pressure — what BMI is ultimately trying to predict.

BMI Prime and the Ponderal Index

Two related numbers are sometimes reported alongside BMI. BMI Prime is your BMI divided by 25 — the upper edge of the WHO healthy band. A BMI Prime of 1.00 is the threshold for overweight; 0.74 is the middle of the healthy band. The Ponderal Index uses height cubed instead of height squared (PI = weight (kg) / height (m)³) and is sometimes preferred for very tall or very short adults because it is more linear across the height range. Our calculator reports both.

How to use BMI well

Treat BMI as a screen that prompts a conversation rather than a diagnosis. A single reading inside the healthy band is reassuring; a reading in the overweight or obese bands is a reason to look at waist circumference, lifestyle and family history, and to talk to a clinician. A reading in the underweight band, especially if recent and unexplained, also deserves clinical follow-up. The number itself is cheap; the follow-up is where the value is.

Other pages on this site

• BMI Formula — the maths, the 703 conversion, and worked examples
• BMI Categories — WHO + Asian-WHO + CDC reference bands
• BMI Chart — printable WHO adult + CDC child tables
• Is BMI Accurate? — when BMI works, when it doesn't
• BMI vs Body Fat — what each measures, and when to use which
• How to Calculate BMI — step-by-step instructions
• Healthy BMI Range — by age, sex, and population

This page is for general information and does not replace medical advice. See our FAQ for quick answers, the Charts page for the full reference tables, or use the calculator directly.