The cost of a National Lottery Lotto ticket has doubled to £2.
The rise, the first since the lottery started in 1994, is part of a package of changes including bigger prizes, says operator Camelot.
Prizes for matching three numbers will rise from £10 to £25. Average jackpots are predicted to rise to around £5m on Saturdays and £2.5m on Wednesdays.
Camelot says this will mean more money for charities. It has raised £30bn for "good causes" since 1994.
Some other prizes will be reduced. Camelot estimates that the reward for matching five balls plus the bonus ball will average £50,000 instead of £100,000.
The prize for matching five balls is expected to average £1,000 instead of £1,500 while the average for matching four balls is expected to go up from £60 to £100.
Extra numbers printed on lottery players' tickets will be entered for a raffle with prizes of £20,000.
Total National Lottery sales have increased by 35% since 2002, when the game was officially renamed Lotto. Some 30 million tickets are reportedly bought every Saturday.