Dates and time

How to Calculate Age in Days Accurately

Count total elapsed date-only days, distinguish inclusive counting, and include leap days without using age multiplied by 365. Learn how UTC normalization, endpoint rules, and calendar boundaries keep the total reproducible across browsers and ordinary time zones, including same-day, cross-year, and February 29 examples with explicit and independently checked counting rules.

6 min read · Practical examplesDates and time

How to Calculate Weeks Between Two Dates

Turn an exact elapsed-day total into complete seven-day periods, remainder days, or a decimal-week value without confusing ISO calendar weeks.

6 min read · Practical examplesDates and time

How to Calculate Complete Months Between Two Dates

Count completed calendar-month anchors and remaining days across short months, leap years, month ends, and reversed date inputs.

6 min read · Practical examplesDates and time

Calendar Difference vs. Elapsed Time Duration

Choose between date-only calendar years, months, and days and continuous timestamp hours, minutes, and seconds across time zones and DST.

6 min read · Practical examplesMathematics

Scientific Calculator Order of Operations

Understand the NumUtility parser's exact precedence for grouping, functions, factorial, right-associated powers, unary signs, multiplication, division, addition, and subtraction.

6 min read · Practical examplesMathematics

Factorials Explained: Formula, Examples, and Uses

Understand n!, 0!, recursive growth, elementary counting uses, and the NumUtility factorial domain from 0 through 170.

6 min read · Practical examplesMathematics

Common Logarithm vs. Natural Logarithm

Compare base-10 log and base-e ln, their inverse exponential relationships, domains, change of base, and NumUtility syntax.

6 min read · Practical examplesConversions

Pounds to Kilograms Conversion: Exact Factor and Examples

Multiply international avoirdupois pounds by the exact kilogram factor and understand why dividing by 2.2 is only approximate.

6 min read · Practical examplesConversions

Grams to Ounces Conversion: Formula and Examples

Divide grams by the exact avoirdupois-ounce value and avoid confusing mass ounces with fluid or troy ounces.

6 min read · Practical examplesMeasurements

Mass vs. Weight: Kilograms, Pounds, and Newtons Explained

Distinguish mass from gravitational weight force and understand what everyday kilogram-pound converters actually calculate.

6 min read · Practical examples