How to Calculate Leap Year and Why it Exists in the First Place

2. The Father of Leap Years

Meanwhile, the Romans had been following a lunar calendar, which has 29.5 days in a month and 355 days in a year. In doing this, they found that they were falling hopelessly out of sync with the seasons. In an attempt to fix this, the Romans would regularly try to add extra days or months, which only seemed to show how significant the demand was for a new calendar.

So in 45 BC, and almost three months out of sync with the calendars, Julius Caesar introduced a new 365-day calendar, with an extra day in a leap year.