Deal or No Deal was a game show with a unique format. No knowledge or reflexes needed, just pure luck and good decision-making skills. It was based on a Dutch format called Miljoenenjacht (Hunt for Millions).
22 boxes held by 22 contestants were presented with money amounts ranging from 1p to £200,000. One of them was randomly selected to play the game. The contestant then took their box and walked to the centre of the set, taking their place at the "pound table", in what Edmonds often referred to as the "crazy chair". Once sitting down the contestant introduced themselves, and after confirming that they selected their box at random, the game would begin.
One at a time, the player was instructed to eliminate the other boxes; the ones s/he thought didn't have £250,000 in them and have the small amounts.
Each round progressively removed fewer cases from the game; in the first round the contestant selected five boxes to be removed, then each new round saw the removal of three boxes at a time.
After each round, the mysterious "Banker" would call offering a money amount based on which amounts were still on the board. If the bigger amounts were gone, then the offer would be low and likewise if the smaller amounts were gone, then the offer would be huge.
When two cases were left, the player had the choice of switching his/her box for the one remaining, provided that some big amounts were still available.
On 1 January 2014, a new feature—"Box 23"—was introduced to the game. At the end of a contestant's game, the contestant was asked if he or she wishes to buy Box 23 for the amount already won on the show. The box contained one of five cards:
- Money Back
The result had the potential to double the contestant's winnings, up to a maximum of £500,000. The contestant also had the potential to leave with half or even lose everything already won.
During special theme shows, the contents of Box 23 were modified, swapping out the "+£10,000" prize for "+£20,000" and the "Money Back" prize for "Quarter".
Starting 29 September 2014, a new gameplay element, the "Offer Button" was added. The button, situated on the contestant's desk, could only be used one time during the contestant's game. When it was pressed, the Banker had to make an offer at that point, regardless of how many boxes had been opened at that stage.
The Offer Button became available after the opening five boxes were selected. To be able to make use of it during his/her game, the contestant had to correctly guess, within a margin of 10%, of the banker's opening offer. The Banker's offer was written and sealed in a capsule and sent to the studio before the contestant guessed the amount. Additionally in special theme shows the contestant additionally won a holiday.