Mega Millions jackpot swells to $400 million
The jackpot has been rolling since Jan. 3.
The biggest lottery prize in the U.S. was a $656 million dollar Mega Millions jackpot in 2012.
Mega Millions changed its rules in October to help increase jackpots by lowering the odds of winning the top prize. That means the chances of winning the jackpot are now about 1 in 259 million. It used to be about 1 in 176 million.