Thank you for using JustAnswer. Yes, it would be legal. What's illegal are "games of chance" (gambling), which has three elements: (1) payment of money or other thing of value, (2) for a chance of winning (3) money or something of value. If you don't have one of these elements, it's not gambling. Sweepstakes, for example, always say "no purchase necessary" to get by the payment of money element that would otherwise make it gambling. So it would be legal. The problem, however, is how do you "police" the contest. That is, how can you accurately verify the weight lost. That's where I see a significant potential liability (as in class action
level, with potentially thousands suing you for breach of contract
. That's likely why you haven't seen these games before, because of the problem in verifying the thing that would make them win: the weight loss. If you have figured out that portion, the other issues are not a problem, as it's a valid contest because it's not based on chance. Hope that clears things up a bit. If you have any other questions, please let me know. If not, and you have not yet, please rate my answer AND press the "submit" button, if applicable. Please note that I don't get any credit for my answer unless and until you rate it a 3, 4, 5 (good or better). Thank you, ***** ***** luck to you!