A gallon of water weighs about 8lb, and that's the biggest swing I've seen in a day so that is my tolerance in the upward direction. Downward I don't worry about now because I weigh more than I want to but when I was skinny my downward tolerance was a line not a difference from what I weighed , so- I'm 5'9" and now maintaining 150 when I'd rather be 140lb, 158 is startling but if it goes away the next day or two I know it was water retention for muscle repair, and I don't worry about weight loss; when I was stressed and 122lb I was very careful about weight loss because 120 is my hard line, and did not worry about weight gain.
So 8 lb in the up, I will watch that but not freak out immediately.