Also note that within some industries, it is common practice to use a week based fiscal month, quarter, and year. The fiscal month does not necessarily start on the first calendar day and run to the last. In these fiscal calendars, the month refers to a specific number of weeks. This is done to even out the irregularity of the lengths of different months so that monthly and quarterly financial reports can be compared with other monthly and quarterly reports without skewing the numbers.
Some combination of two 4-week months and one 5-week month comprise a quarter and the pattern is repeated. E.g. 4-5-4 (Q1) 4-5-4 (Q2) 4-5-4 (Q3) 4-5-4 (Q4).
In this configuration, there are
4 + 5 + 4 = 13;
13 * 7 = 91;
91 * 4 = 364
days in each fiscal year. The beginning of each subsequent year "slides" backwards by one calendar day (two on Leap Years). As a result every five to six years a week is added to the fiscal calendar. The arbitrary selection of whether to add one week at 5 or 6 years is performed by the National Retail Federation.