Leap year most years that are multiples of 4 are leap years. In each leap year, the month of February has 29 days instead of 28. Adding one extra day in the calendar every four years compensates for the fact that a period of 365 days is shorter than a tropical year by almost 6 hours. Some exceptions to this basic rule are required since the duration of a tropical year is slightly less than 365.25 days. The Gregorian reform modified the Julian calendar's scheme of leap years as follows: Over a period of four centuries, the accumulated error of adding a
Chinese calendar solstices, is divided into 24 solar terms. Different versions of the traditional calendar might have different average solar-year lengths. One solar year of the 1st century BC Tàichū calendar is (365.25016) days. A solar year of the 13th-century Shòushí calendar is (365.2425) days, identical to the Gregorian calendar. The additional .00766 day from the Tàichū calendar leads to a one-day shift every 130.5 years. Pairs of solar terms are climate terms, or solar months. The first solar term is "pre-climate" (), and the second is "mid-climate" (). There are generally 11 or 12 complete months, plus two incomplete months around