February 30 was a real date at one point in time in Sweden and the Soviet Union. However, the introduction of this date was temporary. In Sweden, February 30 resulted from an error with calendar conversion in the 18th century. About two centuries later, the Soviet revolutionary calendar featured February 30 as a result of an attempt to cut seven-day weeks into five-day weeks and to introduce 30-day months for every working month.
In 1700 Sweden, which included Finland at the time, planned to convert from the Julian calendar to the Gregorian calendar. Therefore 1700, which should have been a leap year in the Julian calendar, was not a leap year in Sweden. However, 1704 and 1708 became leap years by error. This left Sweden out of synchronization with both the Julian and the Gregorian calendars, so the country reverted back to the Julian calendar.February 30 1712 came into existence in Sweden when the Julian calendar was restored and two leap days were added that year. Sweden’s final conversion to the Gregorian calendar occurred in 1753, when a 10-day correction was applied so that February 17 became March 1 that year. Not everyone was pleased with the calendar reform. They believed this event stole 11 days of their lives.
February 30 existed from 1930-1931 after the Soviet Union introduced a revolutionary calendar in 1929. This calendar featured five-day weeks, 30-day months for every working month, and the remaining five or six days were “monthless” holidays. The abolition of the seven-day week in favor of a five-day week was intended to improve industrial efficiency by avoiding the regular interruption of a non-working day.However, the Gregorian calendar continued to be used in the Soviet Union during this period. This is confirmed by consulting the successive dates in daily issues of Pravda, the official newspaper of the Communist Party, in which February had 28 days in 1930 and 1931, in accordance with the Gregorian calendar. The Soviet revolutionary calendar was eventually discarded as it was difficult to eliminate the Sunday rest tradition. The original seven-day week was restored in 1940.
The 13th century scholar Johannes de Sacrobosco claimed that February had 30 days in leap years between 45 BCE and 8 BCE in the Julian calendar, when February was shortened to give the month of August the same length as the month of July. However, historical evidence relating to the Julian calendar refutes Sacrobosco, who was critical of that particular calendar.