Guides
Longer explanations of the ideas behind the calculators — useful when you want to understand the method, not just get an answer.
All guides
- How to Calculate PercentagesEvery everyday percentage problem, explained with one idea and worked examples.
- How to Convert UnitsA reliable method for any unit conversion, including squared and cubed units.
- Rounding & Significant FiguresDecimal places, significant figures, rounding modes and floating-point surprises.
- How Date Calculations WorkLeap years, month-end rules, inclusive counting, ISO weeks and time zones.
- Mean, Median & Mode ExplainedWhat each average tells you, how to find it, and which one to use.
- Metric vs ImperialHow the two systems are built, where each is used, and quick mental conversions.
- Order of OperationsPEMDAS and BODMAS, the left-to-right rule, and the classic traps.
- Simple vs Compound InterestWhy compound interest grows faster, how compounding frequency matters and the rule of 72.
- How Loan Amortization WorksWhy early payments are mostly interest, how the term changes the cost, and the payment formula.
- Probability BasicsProbability from 0 to 1, combining events, odds, and surprising results like the birthday problem.
How to use these guides
Each guide explains one idea from the ground up, with worked examples whose numbers are calculated by the same code that runs the calculators. They are a good place to start if a result surprises you — for example why a 20% rise followed by a 20% fall leaves you 4% down, why 1 m² is 10,000 cm², or why a loan payment is mostly interest at first.
Where to go next
For quick lookups, the formula sheets and conversion tables collect the essentials on one page. To apply a method to your own numbers, every guide links to the matching calculators.