📜 History of the Gregorian Calendar
The Gregorian calendar replaced the Julian calendar, which had been in use since 46 BCE under Julius Caesar. The Julian calendar assumed a year of exactly 365.25 days, but the actual solar year is approximately 365.2422 days — a difference of about 11 minutes per year. By the 16th century, this had caused the calendar to drift by about 10 days, moving the vernal equinox (important for calculating Easter) away from March 21.
In October 1582, Pope Gregory XIII introduced the reformed calendar, skipping 10 days (October 4 was followed by October 15) and adjusting the leap year rules to prevent future drift. The reform was gradually adopted across the world over the following centuries.
📅 Structure: Months of the Year
The Gregorian calendar has 12 months with a total of 365 days (366 in a leap year). The names of the months come from Latin and Roman traditions.
| # | Month | Days | Latin Origin | Season (N. Hemisphere) |
|---|---|---|---|---|
| 1 | January | 31 | Janus (god of beginnings) | Winter |
| 2 | February | 28 (29 in leap year) | Februa (purification festival) | Winter |
| 3 | March | 31 | Mars (god of war) | Spring |
| 4 | April | 30 | Aperire (to open) | Spring |
| 5 | May | 31 | Maia (goddess of growth) | Spring |
| 6 | June | 30 | Juno (queen of gods) | Summer |
| 7 | July | 31 | Julius Caesar | Summer |
| 8 | August | 31 | Augustus Caesar | Summer |
| 9 | September | 30 | Septem (seven — 7th in old calendar) | Autumn |
| 10 | October | 31 | Octo (eight) | Autumn |
| 11 | November | 30 | Novem (nine) | Autumn |
| 12 | December | 31 | Decem (ten) | Winter |
🗓 Leap Year Checker
A year is a leap year if it is divisible by 4, except for century years (divisible by 100), which must also be divisible by 400.
⚖️ Gregorian vs. Other Calendars
| Calendar | Type | Year Length | Era Start | Current Year (2026 CE) |
|---|---|---|---|---|
| Gregorian | Solar | 365.2425 days | 1 CE (birth of Christ) | 2026 |
| Julian | Solar | 365.25 days | 45 BCE | 2026 (13 days behind) |
| Hijri (Islamic) | Lunar | 354.37 days | 622 CE (Hijra) | 1447–1448 AH |
| Hebrew | Lunisolar | 353–385 days | 3761 BCE (creation) | 5786–5787 AM |
| Persian (Solar Hijri) | Solar | 365.2422 days | 622 CE (Hijra) | 1404–1405 SH |
| Chinese | Lunisolar | 354–384 days | 2697 BCE (Yellow Emperor) | Year 4724 |