How we write, review, and update health content
Health information is YMYL ("Your Money or Your Life") content. That means we hold ourselves to a higher standard than a typical blog. This page describes exactly what that means in practice.
1. What this site is
thehealthcalc.co is a calculator and reference site. It does not diagnose, treat, or give medical advice. The site's job is narrow and we try to do it well: take published population data (the CDC's NHANES survey and peer-reviewed normative studies) and turn it into a percentile lookup the average person can actually use.
If you are looking for diagnosis, treatment, or personalized medical guidance, please talk to a clinician. This site is a screening and education tool, not a substitute for one.
2. Data sources
Every percentile, threshold, and classification on thehealthcalc.co traces back to one of the following primary sources:
- NHANES 2011–2023 (US National Health and Nutrition Examination Survey, CDC/NCHS) — used for body measurements, vital signs, and body-composition percentiles. Grip strength is limited to 2011–2014 (discontinued after that cycle).
- Peer-reviewed normative studies — for metrics NHANES does not collect directly. Examples: Bohannon 2008 (gait speed), Studenski 2011 (walking-speed mortality), Leong 2015 (grip-strength meta-analysis), Ashwell 2012 (waist-to-height ratio), Thomas 2013 / Zhang 2024 (Body Roundness Index), Boer 1984 (lean body mass formula).
We never invent cutoffs, paraphrase secondary sources, or quote studies we have not read. The full citation is published on every tool and guide page under "Methodology".
2. Statistical methodology
Our percentile lookups are computed directly from the published NHANES microdata. For each combination of sex and integer age (18–85), we extract the 10th, 25th, 50th, 75th, and 90th percentiles for the target measurement. The full data pipeline is in our public repository and is reproducible from the CDC's released XPT files.
Fractional ages are linearly interpolated between adjacent integer-age tables. The lookup table is shipped as static JSON with the site — no measurement value ever leaves your browser.
Sample sizes (n) are reported wherever a published threshold was derived from a small or selected sample. Where a metric relies on a formula rather than a distribution (e.g., the Boer equation for lean body mass), the formula is shown explicitly on the tool page.
3. What we review — and what we do not
thehealthcalc.co is a calculator and reference tool, not a medical service. The review we do is therefore about data and methodology, not clinical judgment. The Editorial Team signs off on every page before publication, and the four checks are:
- Source accuracy — every cited statistic, threshold, and risk claim maps to a specific publication, paper, or CDC release. We never paraphrase secondary sources.
- Methodology honesty — the dataset, sample size, and lookup logic are stated on every tool page. If a metric is computed from a formula (e.g., Boer for lean body mass), the formula is shown.
- Scope honesty — we never present a calculator as diagnostic. Every tool page states the population and dataset used and the limits of applying population averages to individuals.
- Plain-language clarity — clinical terms are defined on first use. We do not hide behind jargon to make content sound more authoritative than it is.
What we do not do: we do not provide medical review, clinical endorsement, or health advice. No content on this site should be read as a recommendation, diagnosis, or treatment plan. If you need clinical judgment, talk to a licensed clinician. The full disclaimer is in our Terms of Service and repeated on every tool and guide page.
The Editorial Team's name and role are marked in the page's structured data (reviewedBy) for transparency. That label refers to data and editorial review of this site, not to a medical-reviewer relationship between the site and its users.
5. Update cadence
Health data ages. We follow this review cycle:
- Core dataset (the NHANES lookup table) — re-evaluated every time the CDC releases a new 2-year NHANES cycle, typically every 2 years. Older cycles are kept live until a strict supersession is established.
- Guides — every guide carries a "Last updated" date. High-traffic guides are reviewed at least once per year; lower-traffic guides at least once every 18 months.
- Thresholds and risk cutoffs — re-checked against current WHO / AHA / ACSM guidance on the same annual cycle.
Material changes are noted at the top of the affected page.
6. Independence and conflicts of interest
thehealthcalc.co is editorially independent. We do not accept payment in exchange for ranking a metric higher, we do not run sponsored content, and we do not embed affiliate links inside clinical content. The site is supported by non-personalized advertising (Google AdSense). Ad placements are clearly marked and never interleave with the clinical content of a page.
Members of the editorial team do not hold equity in, or receive compensation from, any company whose products are discussed on this site.
7. What we will not do
- Provide diagnoses, prescribe treatment, or replace a clinician's judgment.
- Recommend specific products, supplements, diets, or programs based on a single calculator output.
- Use fear-based or shame-based framing to drive engagement. Risk language is reported, not weaponized.
- Auto-generate health content without a human editorial pass.
- Publish content based on a single non-replicated study, or on press releases without an underlying peer-reviewed source.
8. Corrections and feedback
If you spot an error — a misquoted statistic, a broken link, an out-of-date cutoff, or a methodology gap — please contact us. We log every substantive correction, fix it on the page, and note the change in the page's "Last updated" stamp.
We do not promise to agree with every suggested change, but we do promise to read every email.
9. AI-assisted content disclosure
Drafting and research support may use large language models, but every published page has been written, fact-checked, and approved by a human editor before release. Statistical tables and percentile lookups are computed from raw data, never from model output.
10. Accessibility
Pages are written to be readable at roughly a 9th-grade reading level, follow semantic HTML structure, and meet WCAG 2.1 AA color-contrast targets. If you find a page that is hard to read or use, please tell us.