Calendar Systems Around The World

Understanding how different cultures and civilizations measure time through their unique calendar systems.

Major Calendar Systems

From ancient civilizations to modern standards, explore the diverse ways humanity tracks time.

Gregorian Calendar

The most widely used civil calendar worldwide, introduced by Pope Gregory XIII in 1582. A solar calendar with 365 days (366 in leap years), divided into 12 months.

Solar Calendar 365/366 days 12 months

Start: January 1, 1 AD
Leap Year Rule: Divisible by 4, except centuries (unless divisible by 400)
Usage: Global standard for civil purposes

Islamic (Hijri) Calendar

A lunar calendar used to date events in Muslim countries and determine Islamic holidays. Consists of 12 lunar months totaling 354 or 355 days.

Lunar Calendar 354/355 days 12 months

Start: July 16, 622 CE (Migration of Prophet Muhammad)
Leap Year Rule: 11 leap years in 30-year cycle
Usage: Religious observances, official calendar in Saudi Arabia

Hebrew Calendar

A lunisolar calendar used for Jewish religious observances. Combines lunar months with solar year adjustments through leap months.

Lunisolar 353-385 days 12-13 months

Start: October 7, 3761 BCE (Traditional creation date)
Leap Year Rule: 7 leap years in 19-year cycle (Metonic cycle)
Usage: Jewish religious observances, official calendar in Israel

Chinese Calendar

A lunisolar calendar traditionally used in China and other Asian countries. Features 12 or 13 months and the famous 60-year cycle with animal zodiac signs.

Lunisolar 353-385 days 60-year cycle

Start: February 2637 BCE (Traditional)
Leap Year Rule: 7 leap months in 19-year cycle
Usage: Traditional festivals, zodiac, feng shui

Julian Calendar

Introduced by Julius Caesar in 45 BCE, predecessor to the Gregorian calendar. Still used by some Eastern Orthodox churches for religious dates.

Solar Calendar 365.25 days 12 months

Start: January 1, 45 BCE
Leap Year Rule: Every 4 years
Usage: Eastern Orthodox religious dates, historical reference

Persian (Solar Hijri) Calendar

Official calendar of Iran and Afghanistan. One of the most accurate solar calendars, with new year (Nowruz) at the spring equinox.

Solar Calendar 365/366 days 12 months

Start: March 22, 622 CE
Leap Year Rule: 8 leap years in 33-year cycle
Usage: Official calendar in Iran and Afghanistan

Calendar Types Comparison

Understanding the fundamental differences between calendar systems.

Solar Calendars

Sun-Based

Based on Earth's orbit around the Sun. Year length approximately 365.25 days. Seasons remain consistent with calendar dates.

Gregorian Calendar Julian Calendar Persian Calendar 365 days (366 leap)

Lunar Calendars

Moon-Based

Based on Moon's phases. Year has 12 lunar months (354-355 days). Months align with lunar cycles but drift relative to seasons.

Islamic Calendar Traditional Hindu Calendar 354-355 days/year 29-30 days/month

Lunisolar Calendars

Hybrid

Combines lunar months with solar year. Uses leap months to keep seasons aligned. Most complex calendar type.

Hebrew Calendar Chinese Calendar 353-385 days/year Leap month every 2-3 years

Week-Date Systems

ISO Standard

Alternative to month-based calendars. ISO 8601 week date format: Year-Week-Day. Used in business and manufacturing.

ISO Week Date 2024-W52-2 52-53 weeks/year Monday = Week start

Today's Date Across Calendars

See how the current date is represented in different calendar systems.

Gregorian

CE (Common Era)

Islamic (Hijri)

~1446 AH

Anno Hegirae

Hebrew

~5785 AM

Anno Mundi

Chinese

Year of Dragon

Sexagenary Cycle

Persian

~1403 AP

Anno Persico

Unix Time

Seconds since 1970

Calendar Systems FAQ

Common questions about different calendar systems.

Why are there different calendar systems?

Different cultures developed calendars based on local astronomical observations, religious beliefs, and practical needs. Some tracked lunar phases for religious purposes, others solar years for agriculture.

Why did we switch from Julian to Gregorian calendar?

The Julian calendar accumulated an error of about 10 days over 1300 years. Pope Gregory XIII reformed it in 1582 to correct this drift and better align with the solar year, improving the accuracy of Easter calculations.

How do lunar calendars handle seasons?

Pure lunar calendars like Islamic Hijri don't align with seasons - they drift by about 11 days per year. Lunisolar calendars like Hebrew and Chinese add leap months periodically to stay synchronized with seasons.

What is the most accurate calendar?

The Persian (Solar Hijri) calendar is considered one of the most astronomically accurate, with an error of only 1 day in 110,000 years. The Gregorian calendar has an error of 1 day in 3,236 years.

Why does the Chinese New Year date change?

The Chinese calendar is lunisolar, so its new year falls on the second new moon after the winter solstice. This causes it to vary between January 21 and February 20 in the Gregorian calendar.

How do software systems handle multiple calendars?

Modern systems store dates in UTC or Unix timestamps (Gregorian-based) and use locale-aware libraries to convert and display dates in different calendar systems. Libraries like ICU (International Components for Unicode) provide comprehensive calendar conversion.