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.

Check whether an ISO calendar date is February 29 of a leap year. 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]

Leap day

The resulting leap day returned as a boolean.

• 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.

• Leap Year Checker

  Check whether a Gregorian calendar year is a leap year.

• Is Future Checker

  Check whether an ISO 8601 date or date-time falls after the UTC day of a reference date-time.

• Is Past Checker

  Check whether an ISO 8601 date or date-time falls before the UTC day of a reference date-time.