In the book's future, advertising's relentless search for new markets has led to a world where, by O.N.A.N. dictate, years are referred to by the name of their corporate sponsor.
CHRONOLOGY OF ORGANIZATION OF NORTH AMERICAN NATIONS’ REVENUE ENHANCING SUBSIDIZED TIME™, BY YEAR
- Year of the Whopper
- Year of the Tucks Medicated Pad
- Year of the Trial-Size Dove Bar
- Year of the Perdue Wonderchicken
- Year of the Whisper-Quiet Maytag Dishmaster
- Year of the Yushityu 2007 Mimetic-Resolution-Cartridge-View-Motherboard-Easy-To-Install-Upgrade For Infernatron/InterLace TP Systems For Home, Office Or Mobile (sic)
- Year of Dairy Products from the American Heartland
- Year of the Depend Adult Undergarment
- Year of Glad
Most of the action in the novel takes place in the Year of the Depend Adult Undergarment, or Y.D.A.U., which is probably AD 2009, taking the Year of the Yushityu... (the lengthily titled 6th Subsidized Year) as 2007. Critic Stephen Burn, in his book on Infinite Jest, argues convincingly that Y.D.A.U. corresponds to 2009: the MIT Language Riots took place in 1997 (n. 24) and those riots occurred 12 years prior to Y.D.A.U. (n. 60).
Other evidence that Y.D.A.U. is 2009 includes the mention that November 20, Y.D.A.U. is a Friday (p. 198). Years on which November 20th is a Friday include 1992, 1998, 2009, 2015, 2020, etc. The most fitting of these is 2009.
It is also possible that Y.D.A.U. is 2008, as Matty Pemulis turns 23 in Y.D.A.U. (p. 682). Matty's (and Mike's) father came over in 1989 when Matty was "three or four" (p. 683). If Matty had been three and four in 1989, he was born in 1985, which mean he turns 23 in 2008.
It's possible that Wallace deliberately kept the time of IJ somewhat fluid or simply couldn't be completely consistent throughout the book's 1000+ pages; Wallace altered some details between the original and paperback editions of the book. For instance, in the first edition, during Hal's conversation with his disguised father, he claims that he'll be "thirteen in June." However, in the paperback edition, this is altered to "eleven in June."