CalcDuck is an independent site that publishes 234 free calculators covering finance, health, math, unit conversion, dates, home projects and everyday questions. It is maintained by the CalcDuck Editorial Team — a name for who is accountable for what gets published here, not a claim about how many people that is.
There is no advertising network, no lead-generation form and no newsletter signup. Nothing on the site is designed to route you to a product.
How a calculator gets published
Every calculator is a small program with a written specification. All 234 have been through the same four checks, and new ones go through them before they are added:
- The formula is taken from a published source, not reconstructed from memory. Where a formula has a name — Mifflin-St Jeor, Widmark, Naegele, Cochran — the page names it and links the source.
- It is tested against known reference values. Each calculator ships with automated tests containing worked values from textbooks, standards documents or the source paper, plus property tests (converting back and forth, checking parts sum to the total, cross-checking a closed-form answer against a simulation).
- Every number in the article is recomputed. The figures in the explanations and worked examples are checked against what the calculator actually outputs, because a page whose prose contradicts its own tool is worse than no page.
- A second pass tries to break it. Each calculator is re-audited by someone who did not write it, with instructions to find errors rather than confirm correctness — re-deriving the maths independently and re-checking constants against the original source.
That process has caught real mistakes before publication, including an outdated tax rate, a formula constant that did not match the paper it cited, and lookup-table values that did not match the source they were credited to. It will not have caught everything.
What these calculators are not
They are calculations, not advice. A mortgage calculator does not know your credit file; a body-fat estimate is not a health assessment; a blood alcohol estimate cannot tell you it is safe to drive. Pages that touch health, pregnancy, alcohol or money say this plainly, and where a professional should be involved, they say that too.
Rules that change — tax brackets, contribution limits, lending regulations — are deliberately not baked in. You enter your own rate, because a hardcoded figure quietly becomes wrong and a wrong figure presented confidently is the failure mode we are most concerned about. For the same reason there is no currency converter or stock calculator here: those need live data we cannot promise to keep accurate.
Found something wrong?
Corrections are welcome and taken seriously — if a number here is wrong, it is wrong for everyone who used it. Email hello@calcduck.com with the page and what you expected instead. Include your source if you have one, and it will be checked against ours.
More detail on the checking process is on the methodology page.