Every day? Once a week?
How often to weigh one's self? What I have found is that my weight fluctuates massively, this means weighing yourself every day can prove frustrating, "wow I lost 1.1kg" to "what the hell I am up by 1kg" all in the space of a couple of days. Two causes, hydration and contents of the digestive system. Drink a bottle of water and you have put on a pound, go to the loo and you might lose the same. Similarly weekly weighing can cause the same frustrating results for some.
So what to do? Well I am weighing myself once a day more or less, I'm using a wifi scale by Withings to do this for convenience and I consider the trend in my weight but also my "new minimum". The trend is basically what your weight does on average in the week, the withings app and website show this nicely actually. The "new minimum" is just that when I see a weight lower than one I have seen in recent history I know that previously no amount of dehydration or bowel movements could have achieved it, that means something even if I am heavier the next day!