If you are on a maintenance plan and happily sticking to an exercise and healthy eating plan, then weighing yourself once a month is best. But if you are working daily on calorie restriction and working an exercise plan to loose weight, once a month may not be enough. I had been weighing myself once a month, and ended up waiting till the last 2 weeks of the month to follow my eating plan. :-o
Most weight loss programs recommend weighing once a week or less. Weighing at the same time of day is helpful as well. You will almost certainly weigh more at night than you do in the morning. Weighing right before you hop in the shower will give you the ol' Birthday Suit weight. For a long time I was a once a week weigher. Monday morning before breakfast. That was me. But it seemed like I suffered from accountability issues in that amount of time as well.
Either I wait until Friday to start following my plan. Or, I get a great number on Monday which makes me work hard until Friday and then the weekend is full of 'rewarding' myself. Then I get a bad number on Monday (water weight from those salty rewards I'm sure) and go off plan for the next week.
I've been reading some recent research on this topic and found a study published in the Annals of Behavioral Medicine that suggests that:
"adults who were trying to lose weight as well as overweight adults who were trying to prevent weight gain found that those who weighed themselves more often lost more weight and prevented more weight gain over two years than those who weighed themselves less frequently." Taken from This Site
Apparently there is changing thinking on the frequency of weigh ins. Though, I would like to point out that some people are more sensitive than others. If you can't handle seeing a different number on the scale every day, then this approach may not be for you. It can be a fantastic tool to determine foods that cause water retention and stay in tune with your body's monthly clock. But it can be discouraging to see 3-4lb fluctuations every day when you are working so hard.
I'm trying to weigh more often than weekly. So far so good. I'm not weighing daily, but M - W - F...okay and Saturday. So far this week I've had a fabulous number every day. It's kept me stoked and fighting another day. I'm fighting to keep that number until Monday which is my "official" weigh in day.