January was a 5-week month. The National Retail Federation, whose calendar is used by NPD, periodically has a "53-week year," basically something like a "fiscal leap year" to account for a calendar year being not exactly 52 weeks (a standard year is 52 weeks and one day; a leap year is 52 weeks and two days). Normally the "4-4-5" calendar divides the fiscal year up into 52 weeks, with March, June, September, and December being 5-week months and all the others being 4-week months. But when they decide that a 53-week year is needed, the NRF will make the January sales period a 5-week month. Previous 5-week January periods were in 1996, 2001, 2007, and 2013, so they do this once every 5 to 7 years as needed.