Online Calculation Tools
Free calculators for dates, money, geometry, health, and unit conversion. Every tool runs in your browser, needs no sign-up, and comes with a written explanation of the method it uses.
Financial Calculations
What makes these calculators different
- Each page explains the formula it applies and the convention it follows, so you can check the result rather than trust it blindly.
- Edge cases are documented: leap years, month-end clamping, imperial versus US gallons, and the difference between metric PS and mechanical horsepower.
- Worked examples use realistic numbers and show the intermediate steps, which is where most manual calculations go wrong.
- Sources are cited to standards bodies such as BIPM, NIST, ISO, WHO, and EFSA rather than to secondary summaries.
- Every page carries a review date and states what its method cannot tell you. A calculator that never admits uncertainty is misleading by omission.
- Each language is written independently rather than machine-translated, so the examples and conventions match how the calculation is actually used there.
Picking the right tool
If you are counting the gap between two dates, decide first whether you need inclusive or exclusive counting, because that alone changes the answer by a day. For anything involving money over time, check whether the rate you have is nominal or effective. For unit conversion, remember that area factors are squared and volume factors are cubed - applying a linear factor to an area is the single most common conversion error, and it is off by a factor of ten or more.
Accuracy and limitations
These tools are informational. Health calculators use population-level equations that carry real individual error, financial projections assume a fixed rate that reality will not deliver, and date calculations follow the most widely used convention where several exist. Every page states which assumptions it makes. For legal, medical, tax, or financial decisions, confirm the result with a qualified professional.