What is the Gregorian Calendar?

The Gregorian reform reduced the long-term drift of the Julian calendar and is now the primary civil calendar used internationally, though many communities retain parallel religious or traditional calendars.

How the calendar is structured

365 days; leap years divisible by 4 except century years unless divisible by 400.

Where and why it is used

Region: Worldwide. Primary context: Dominant international civil calendar.

History and development

The system belongs to the Modern layer of the archive. Its origin is summarized as 1582 reform. CalculatorWiser separates historical reconstruction, religious observance, civil use, and modern technical standards so different systems are not treated as though they all work the same way.

Visual reference gallery

Conversion and accuracy notes

Some calendar systems can be converted deterministically with modern algorithms. Others depend on observation, local authority, historical reconstruction, or regional practice. CalculatorWiser marks those distinctions rather than presenting uncertain dates as exact.

Research trail

This entry is part of the research-backed World Calendar Archive. Primary research anchor for this entry: Unicode CLDR / ISO.