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Calculation Categories
Eight subject areas, one method throughout: every page gives you the formula, defines each variable, works through real numbers and tells you where the result stops being valid.
8 categories · 362 published calculations · free calculators on every topic.
Finance
103 calculationsInterest, loans, investments and taxes — learn how every financial number is derived and which input moves it most before you plug anything into a calculator.
Includes Investing, Insurance, Retirement and more
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Math
55 calculationsPercentages, ratios, series and geometry — the arithmetic behind everyday numbers, worked step by step with the formula, the variables and a check you can repeat.
Includes Geometry, Statistics, Algebra and more
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Science
47 calculationsPhysics, chemistry and astronomy formulas explained with their units, constants and worked examples, plus the range in which each law actually holds.
Includes Physics, Chemistry, Mechanics and more
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Health
26 calculationsBMI, calorie and fitness metrics — what each formula measures, which population it was built for, and exactly where its limits begin.
Includes Nutrition, Body Composition, Pregnancy and more
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Business
33 calculationsMargins, markups, ROI and pricing — the numbers operators actually use to make decisions, with the algebra behind every one of them.
Includes Ecommerce & Marketplaces, Operations, Marketing and more
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Education
19 calculationsGrades, GPA and study metrics explained so students and teachers can verify the result by hand, including the weighting rules behind each score.
Includes Grades, Grading, Study Skills and more
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Everyday Life
53 calculationsCooking, travel, home and time calculations that come up outside any classroom, with the everyday assumptions spelled out rather than hidden.
Includes Home, Home Improvement, Work and more
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Unit Conversion
26 calculationsLength, mass, temperature, pressure and more — every conversion shown with its factor and its exact definition, not hidden behind a button.
Includes Temperature, Length, Mass & Weight and more
Browse Unit Conversion calculations →How the library is organised
Categories group calculations by the kind of question you are asking. Within each one, subtopics collect closely related methods — compound interest sits with other investment calculations, and temperature conversions sit with other unit conversions — so you can compare two approaches without losing the context they share.
Every calculation page follows the same structure: a quick answer you can quote, the formula with each variable defined, the steps worked on real numbers, a calculator to try your own inputs, common mistakes, related methods, a short FAQ and the references behind the figures. The numbers are recomputed rather than copied, so you can reproduce them by hand or in a spreadsheet.
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The same calculations are also indexed by what you want to do with them: read the full list, open a tool, look up an equation, find a table, or see two methods compared on identical numbers.