Start with the question, then check the assumptions.
A calculator is most useful when the input matches the question you are trying to answer. The guides below use the same definitions and examples as the tools on this site. They are explanations, not personalized financial, medical, legal, or professional advice.
Mortgage payment guideEstimate a fixed-rate principal-and-interest payment and learn what is not included.BMI calculator guideEnter height and weight consistently, understand the equation, and recognize its limits.Percentage calculator guideFind a part as a percentage of a whole and avoid common denominator mistakes.Date and time guideUse date, elapsed-hours, and UTC-offset tools with the right time assumptions.
Check a result before acting on it.
Review units, dates, rates, and whether the tool’s assumptions fit your situation. For decisions involving a lender, health professional, employer, contract, or public service, use their records and guidance as the controlling source.