Why is the first day of April on the Gregorian calendar March 30th?

The calculation method is easy to remember.

1. Calculation method: The ancient calendar adopted the method of combining the lunar calendar with the solar calendar, and divided the time into 24 solar terms and 12 months. Due to different calculation methods, April 1 day (lunar calendar) corresponds to March 30th (solar calendar).

2. Easy to remember: In order to facilitate people's memory, the ancients marked the adjusted date as "day" instead of "month". The first day of April in Gregorian calendar is actually the last 1 day in March of that year, that is, March 30th.