The lottery starts at a base of $12 million. I'm not sure if its ever worth less than that. When people buy tickets, 50% of their ticket goes towards the jackpot. When no one wins, another (conservative) estimate of how many people will buy tickets is made, and a new jackpot is set. When the lottery gets to a big number and no one wins, it starts making news. This is the largest amount ever available as a single prize. The thing that allows this lottery to grow so fast is because it's available pretty much throughout the U.S. The previous jackpot was $363 million, which means about 550 million or more tickets have been sold since Tuesday.