Use this calendar calculation when dates follow the stated calendar and you need a reproducible boundary, interval, ordinal, week, or classification result.

Date

Required string input.

Return ISO weekday number and English name for an ISO calendar date. The tool evaluates the supplied inputs together and returns the named outputs below; it does not infer omitted operating conditions or change the units shown.^[1]

ISO weekday

The resulting iso weekday returned as an integer.

Weekday name

The resulting weekday name returned as a string.

• Calendar dates are not elapsed-time instants by themselves. Time zones, daylight-saving transitions, locale-specific week rules, inclusive endpoints, holidays, historical calendar reforms, and proleptic-calendar assumptions can change an apparently simple result.
• Use finite inputs in the displayed units and preserve more precision than the final presentation requires. Independently verify safety-critical, financial, compliance, or production decisions.

Store instants with an explicit time zone when time of day matters, and document whether interval endpoints are inclusive. Supply a jurisdiction-specific holiday calendar for business-day decisions.

• Days in Quarter Calculator

  Return the number of calendar days in the Gregorian quarter containing an ISO date.

• ISO Week Number

  Return the ISO-8601 week number and week year for a calendar date.

• Days in Month Calculator

  Return the number of days in a Gregorian calendar month.