Methodology and corrections

How each calculator is built

Every calculator separates the mathematics from the page. The calculation lives in its own module that knows nothing about the web page, and the page only collects the inputs and displays the result. This keeps each formula in one place and makes it possible to test it on its own.

Each calculation is tested automatically with cases whose answers can be checked by hand, with extreme values such as zero or the largest accepted number, and with invalid input such as empty fields, negative numbers or text. The worked example printed on each page is also checked by an automatic test against the same calculation, so the example and the calculator cannot drift apart.

Where formulas and constants come from

• Mathematical formulas, such as the area of a circle or the standard deviation, are the standard textbook definitions, shown on each page in the section called Formulas used.
• Unit definitions, such as the exact length of an inch or a mile, follow international standards. Where a page relies on an external definition, it lists the source in a section called Sources and references.
• Networking rules on the IP subnet calculator follow the public Internet standards (RFCs) listed on that page.
• Values that are naturally approximate, such as the density of an ingredient or the weight of a cup of flour, are labelled as approximate wherever they are used.

Estimates, scope and the limits of the results

The results are general information. Calculators about pay, income, overtime, margins, discounts or fuel give estimates from the numbers you enter; they do not apply tax rules, labor law, contracts or accounting standards, which vary by country and situation. Calculators about grades follow common conventions that schools may not share. Tools related to walking or running do arithmetic only and are not health, training or medical advice.

None of the results is professional advice. For decisions with legal, tax, financial, medical or academic consequences, check the rules that apply to you or ask a qualified professional.

Rounding, precision and input limits

Calculations use the full precision of the computer. Results are rounded only when they are displayed, with a number of decimals suited to the quantity. Amounts of money are rounded to the cent, and the breakdown shown always adds up to the total shown.

Each field has a limit on the largest value it accepts. The limits are not rules of any law or standard; they exist to catch typing mistakes and to avoid numbers too large to be meaningful.

Corrections

If you think a result, a formula, an example or a statement on this site is wrong, please tell us which page it is on and which values you entered. Contact address: [email protected].

Reports are checked against the formula and, where relevant, against its source. If the report is correct, the calculation or the text is fixed and a test is added so the same error cannot return. When a correction materially changes the results a page gives, the page will say so.

Who is responsible

This site does not present articles under individual author names. The person or organization responsible for the content is Micaela Huarte.