Your weight is submitted weekly to the UFC and whenever USADA tests you. Whatever this number is the weight you will fight at period, no exceptions. If you lose or gain weight via diet, then you can change weight classes, but dehydration would be banned 100%. Fights are made based upon the current ranges. 136-146, 146-156, etc. At this point, everybody cuts weight and it only hurts the fighters performances. Instead of rewarding fighters who dehydrate themselves to near death, the weight class structures should reward the fighters who stay lean and in-shape year round. Get too big and you are forced to move up. The fighters who manage their weight properly should be rewarded with better performances. We should see the best fight the best, not who can cut the most weight without killing themselves. There is no reason why Max should be fighting Frankie, or Cejudo fighting Moraes, etc. Most fighters would be fighting the same pool of fighters, and the outliers would be reshuffled to their proper weight class. Anyone who says cutting weight has zero effect on their performance are just lying to themselves. We have seen numerous examples who fighters moving up and looking much better even if they have to fight bigger fighters. Imagine the performances if they didn't have to cut weight.