Introduction
A calendar date difference measures elapsed days between two dates. A business-day count includes only the working days defined by the chosen calendar.
The two results answer different questions, so they can differ substantially even for the same start and end dates.
Key concept
Calendar days normally include weekends. Business days commonly exclude Saturday and Sunday, while public holidays require a specific holiday calendar that a basic calculator may not know.
Example
From Friday to the following Monday, the elapsed calendar difference is three days. A Monday-through-Friday business-day method may count only one working-day transition, depending on whether the endpoints are included.
Common mistakes
Inclusive counting includes one or both endpoint dates, while exclusive counting measures only the interval between them. Always confirm which convention the result uses.
Business days are not universal. Workweeks and official holidays vary by country, organization and schedule.
Which tool to use
Use a date-range calculator for elapsed calendar time. Use a business-days calculator for a weekday-based estimate, then adjust separately for holidays or organization-specific closures if required.