I weigh first thing in the morning. I get up, go straight to relieve my bladder and then to the scales! I normally always weigh about 3-4 pounds less than I do in the evenings. It's because overnight your body has not had anything going into it and whatever else goes on! During the day you're eating and drinking, etc so you weigh more. I know a lot don't agree but I weigh myself every morning! I have to! This way I know if I'm going up or down. It keeps me sane! It's a ritual!
Good Luck!