4and5

The 4–4–5 calendar is a method of managing accounting periods, and is a common calendar structure for some industries such as retail and manufacturing.
The 4–4–5 calendar divides a year into four quarters of 13 weeks grouped into two 4-week "months" and one 5-week "month". The grouping of 13 weeks may also be set up as 5–4–4 weeks or 4–5–4.
When this type of calendar is in use, reports with month-by-month comparisons or trends are flawed as one month is 25% longer than the other two. It could still compare a period to the same period in the prior year, or use week by week data comparisons.
Its major advantage over a regular calendar is that the end date of the period is always the same day of the week, which is useful for shift or manufacturing planning as every period is the same length.
A disadvantage of the 4–4–5 calendar is that it has only 364 days (7 days x 52 weeks), meaning a 53rd week will need to be added every five or six years: this can make year-on-year comparison difficult.

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