About CalculateWise
CalculateWise is a collection of 152 free online calculators for personal finance, health and fitness, running, pregnancy dates, construction estimating, and everyday math, plus short guides that explain the formulas behind them. Every calculator runs in your browser; nothing you type is sent to a server.
Who runs the site
CalculateWise is operated by F4 Labs. Articles are published under the CalculateWise name rather than individual bylines. Questions, corrections, and requests go to [email protected]. See the contact page for what to include in a report.
How the calculators are built
Each calculator is a small, self-contained definition: its inputs, the formula, the validation rules, and the explanatory text live together in one file. The formula is written out on the page under “How it works” or “How the calculation works” so you can check it against the result. Where a calculator relies on a published standard, equation, or official figure, the source is named on the page. At the moment 16 calculators link directly to primary sources such as IRS publications, government health references, or the original equation’s publication, and more are being added as pages are reviewed.
Machine-readable copies of every calculator definition, including the formula and a default test vector, are published at /registry/index.json. This is the same code the page runs, so anyone can inspect exactly what a result is based on.
How results are checked
The project includes an automated test suite that runs every calculator with its default inputs and fails if a result is missing, non-numeric, or cannot be displayed. Calculators whose figures have been corrected carry regression tests pinned to published reference values (for example, the 2025 IRS tax rate schedules and the worked example on the tax refund page), so the same error cannot return unnoticed. The ratio calculator’s simplify, equivalent-ratio, and proportion logic is pinned the same way.
Accuracy and limitations
The calculators apply the stated formula to the numbers you enter. They are estimates for planning and learning, not professional advice. Health calculators such as BMI, body fat, BMR, and due-date estimates use population equations that do not account for an individual’s medical history; financial calculators simplify tax law, lending rules, and market behaviour. Each page states its own assumptions and what it leaves out. For decisions that depend on the result, confirm it with a qualified professional or the official source.
Corrections
If a result looks wrong, a source is out of date, or a guide contains an error, email [email protected] with the page address and the inputs you used. Confirmed errors are fixed in the calculator definition, covered by a regression test, and the page’s “Last updated” date is changed. Guides that are revised show an “Updated” date next to the publication date.
Funding and advertising
The site is free to use and is funded by advertising served through Google AdSense. Advertising does not influence which calculators exist, how they are built, or what the guides say. Details on analytics and ad cookies are in the privacy policy; the rules for using the site are in the terms of use.