1. How We Build a Calculator
Every calculator and converter is written, tested and maintained by the CalculatorEver editorial team. We start from the formula or the rule, write it down in plain steps, and then build the tool so that it follows those steps exactly. The formula is shown on the page, with a worked example, so you can see where an answer comes from and repeat it by hand if you like.
The numbers you type are worked out in your browser. They are not sent to our servers (see the Privacy Policy).
2. Where the Formulas and Numbers Come From
Where a rule is set by an organization, we use that organization's own figures, and we say so. On the pages that depend on them, a Sources list at the bottom links to the original pages. For example:
- Health pages use the World Health Organization, the CDC, ACOG (the American College of Obstetricians and Gynecologists) and the American Council on Exercise.
- US pay and retirement pages use the Internal Revenue Service and the Social Security Administration.
- Sales tax and VAT pages use state and government figures and the Tax Foundation's published tables.
- Unit converters use the exact definitions wherever one exists, such as 1 inch = 2.54 centimeters, and a stated value where it does not.
Some formulas are well known methods rather than official rules, such as the Epley one rep max formula or the Mifflin-St Jeor equation. We name the method on the page so that you know which one is in use.
3. How We Test the Answers
We test our answers against independent calculations. For many of our unit converters we run automated tests that type values into the page, in the same way a visitor would, and compare the result with exact whole-number maths. These tests make thousands of checks per page, covering the answers, the tables, the share links and the way the page looks on a phone.
We also test calculators against worked examples, and we re-run the checks when a page changes.
4. Rounding and Units
We keep the full precision while a calculation runs and round only when an answer is shown, so rounding in one step does not add up across the next ones. Many pages let you choose how many decimals to show. Money is shown to the cent where the cents matter.
Where a country uses different units or names (for example US and UK fluid ounces, or US and UK spelling), we show both and say which one a figure uses.
5. Keeping Pages Up to Date
Most calculators show a Last updated date. Figures that change, such as tax limits, withholding tables and VAT rates, are reviewed when the new figures are published, and the date on the page changes when we do. A page without a date does not depend on rates that change.
6. What Our Tools Cannot Do
Our results are estimates for general information. A real loan offer, tax bill, medical result or exam grade depends on details we cannot see. Please read the disclaimer, and check important decisions with a qualified professional or the organization concerned.
7. Report a Mistake
If a result looks wrong, please tell us. Send the name of the calculator, the numbers you typed and the answer you expected to contact@calculatorever.com or use the contact page. We aim to reply within 2 to 3 working days. When we confirm a mistake, we fix it and change the Last updated date.