A quick bit of research finds claims ranging from two weeks to four years ... both are probably unlikely extremes. Ecover specifically states 365 days. Seventh Generation 360 days. Citra-Dish powder does state 4 years. Dishwasher powder tends to absorb moisture. Signs of staleness include a swollen box and clumping. A typical-size box of WM Great Value usually lasts months for me. Assuming I didn't miss recording a purchase, I bought a box in June 2008 and in Feb 2009. I don't buy the larger-size packages.