People have created thousands of calendar systems throughout history. Every major ancient civilization, regional tribe, and religious movement tended to develop its own way of tracking time.

While the Gregorian calendar is the universal standard for global business, politics, and aviation, there are roughly 40 to 50 calendars still actively used today for religious, traditional, agricultural, or national purposes.

Almost every calendar ever invented falls into one of four main structural designs, based on how they track the sun, the moon, or both.

Universal Calendar Designs

Solar Calendars (Tracking the Sun)
These calendars are based entirely on the solar year (the time it takes Earth to orbit the sun—roughly 365.24 days). They completely ignore the phases of the moon.

Lunar Calendars (Tracking the Moon)
These calendars are based strictly on the synodic month (the time between two new moons—roughly 29.5 days). They ignore the solar year entirely.

Luni-Solar Calendars (The Hybrid Approach)
These calendars try to get the best of both worlds: they track the phases of the moon for their months, but they use a clever trick to keep the overall year aligned with the sun and the seasons.

Arbitrary / Rule-Based Calendars
These systems do not tie themselves to the strict cycles of astronomy. Instead, they rely on rigid mathematical math or completely distinct intervals.

Ancient Roman Calendar

Asatru Calendar

Babylonian Calendar 7/8/26

Babylonian Calendars 7/8/26

Bahá’í Calendar 7/8/26

Biblical Calendar Of Events 7/8/26

Cosmic Calendar, The 4/6/26

Enoch Calendar 7/8/26

Father’s Calendar 7/8/26

God’s Calendar 4/6/26

Masonic Notable Dates 4/1/26

Occult Holidays Or God’s Holy Days

Other Dates of Observances 4/1/26

January Calendar

February Calendar

March Calendar

April Calendar

May Calendar

June Calendar

July Calendar

August Calendar

September Calendar

October Calendar

November Calendar

December Calendar

Notes on Various Holidays