How many months in a year have 30 days?

The number of days in February depends on the year. In a common or non-leap year, February has 28 days. However, in a leap year, which occurs once every four years, February has 29 days.

The reason for this difference is that a common year is 365 days long, which is not evenly divisible by the number of days in a month. To keep the calendar year synchronized with the astronomical year, which is approximately 365.2422 days long, a leap year is introduced with an extra day added to February, making it 29 days long. This extra day is added because it takes the Earth approximately 365.2422 days to orbit around the Sun once, so adding an extra day every 4 years helps to keep the calendar year in alignment with the solar year.