How we build a calculator
Every calculator on HisabWeb begins with a published, peer-reviewed formula or an official-organization standard (e.g. the WHO's BMI thresholds, CDC growth charts, standard mortgage amortization). We implement the formula in code, write a plain-language explanation, and verify the output against worked examples from the source documentation. A calculator does not go live until at least three test cases - including edge values - match the reference numbers from the original source.
Which sources we rely on
For health calculators: the World Health Organization (WHO), the Centers for Disease Control and Prevention (CDC), and major peer-reviewed medical references. For finance: the published amortization standards used by central banks and consumer-protection agencies. For math, physics, and chemistry: established textbook formulas with cited derivations. We list the specific sources we used at the bottom of each calculator page so you can verify our work yourself.
How we review and update
Every calculator has a visible "Last reviewed" date. We re-check each calculator at least once every 12 months - or earlier if a sourcing organization (WHO, CDC, etc.) updates its guidance. When we change a formula, threshold, or interpretation, the "Last reviewed" date updates and the change is reflected in the rendered content.
What we don't do
We do not attribute calculators to real medical professionals, financial advisors, or engineers who have not personally reviewed and approved that specific calculator. If a real specialist's name appears on a page, it is because that specialist worked with us on that page. As of today, HisabWeb has no individually named external reviewers - and we say so honestly rather than fabricating credentials to look more authoritative.
Found an error?
If a calculator produces a result that doesn't match an authoritative source, please tell us. We treat error reports as a priority and aim to respond within 48 hours. Use the "Send feedback" button on any calculator page, or write to us at hello@hisabweb.com.
What HisabWeb is not
HisabWeb provides general-purpose calculation tools. It is not medical, legal, financial, or engineering advice. For decisions that affect your health, finances, or safety, please consult a qualified professional. We do our best to be accurate, but the responsibility for acting on a result is yours.