WhenMath

Business Days & Work Calendar

A "business day" is not a fixed unit the way a calendar day is: it depends on which days of the week count as working days, which holidays are excluded, and whether the count starts from the day you are standing on or the day after it. This category covers everything that requires a working-day calendar rather than a plain one: adding or subtracting business days, counting business hours across multiple dates, finding the nth or the last business day of a period, and measuring the impact a specific holiday calendar has on a result.

The default counting rule

Adding business days treats the start date as day zero: a Monday plus one business day is Tuesday, not Wednesday. A custom workweek (for example, a Sunday-to-Thursday schedule) and a set of excluded dates are both first-class inputs, not an afterthought bolted onto a Monday-to-Friday default.

Holiday data is a convenience, not a determination

Public-holiday presets on this site are calendrical convenience data pulled from a vetted static source, not a legal or contractual determination. They do not establish whether your specific employer, contract, court, or jurisdiction actually treats a given date as non-working; where that distinction matters, the result says so plainly, and a custom excluded-date list always overrides a preset.

Where to go next

Once a business-day count needs to become an actual project deadline with buffers or phases, see Deadlines & Project Capacity. For hours worked within those working days rather than which days count at all, see Work Hours, Timecards & Shifts.

Business Days & Work Calendar tools