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Proleptic Gregorian Calendar

The proleptic Gregorian calendar extends the Gregorian calendar's rules backward in time before 1582, providing a consistent dating system for astronomical calculations, computer systems, and historical research, though it creates an artificial uniformity that differs from the actual calendar systems used throughout history.

Rata Die

Rata Die is a day-counting system that represents dates as integers counting from January 1, 1 AD, providing a computationally efficient method for date arithmetic and storage while sacrificing human readability.

Hindu Calendar Systems

Hindu calendar systems are sophisticated lunisolar timekeeping methods that combine lunar months with solar year corrections, serving as the foundation for religious festivals, agricultural cycles, and cultural life across the Indian subcontinent for over 3,000 years.

Śaka Era

The Śaka Era is a calendar system beginning in 78 CE that originated with Central Asian Śaka rulers and now serves as the foundation for India's official national calendar, demonstrating remarkable historical continuity from ancient times to the present day.

Indian National Calendar

The Indian National Calendar is India's official civil calendar system, adopted in 1957, which combines the ancient Śaka era dating system with modern astronomical calculations to provide a unified temporal framework that balances cultural heritage with administrative efficiency.

Shaka Samvat

Shaka Samvat is a lunisolar calendar system beginning in 78 CE that serves as India's national calendar alongside the Gregorian system, playing a crucial role in Hindu religious practices, government documentation, and cultural traditions across South and Southeast Asia.

Vikram Samvat

Vikram Samvat is a traditional Hindu lunisolar calendar beginning in 57 BCE that remains widely used across India and Nepal for religious festivals, agricultural planning, and cultural observances.

Hindu calendar

The Hindu calendar is a sophisticated lunisolar system combining lunar months with solar year adjustments, serving as the foundation for Hindu religious festivals, agricultural activities, and astrological practices across the Indian subcontinent for over two millennia.

Ancient Egyptian calendar

The Ancient Egyptian calendar was a 365-day solar calendar system that divided the year into three 120-day seasons plus five additional days, serving as both an administrative tool and religious framework that profoundly influenced later calendar systems including the Roman Julian calendar.

Armenian calendar

The Armenian calendar is a traditional 365-day calendar system beginning in 552 CE, used primarily by the Armenian Apostolic Church for religious observances and by Armenian communities worldwide to maintain cultural identity and coordinate liturgical celebrations.

Coptic Calendar

The Coptic calendar is a 365/366-day calendar system derived from ancient Egypt, featuring 12 months of 30 days plus a 13th month of 5-6 days, used primarily by Coptic Orthodox Christians and as an official calendar in Ethiopia.

Ethiopian calendar

The Ethiopian calendar is a 13-month solar calendar system used in Ethiopia and Eritrea that runs approximately 7-8 years behind the Gregorian calendar, serving as both a practical timekeeping tool and a symbol of cultural independence.