|My weight on Mars (July 2013). That makes 927 reasons to go to Mars.|
Guideline, The First (Primus):Get on a scale at least once a week. Knowing how far you've gone requires knowing where you started. If you're the overly analytical sort (like me) you can do it more often; however, in that case, you must keep a careful record and look at the trend over several days, as your weight can easily vary by several pounds just based on varying degrees of hydration and the physical weight of food still in your digestive tract.
Regardless of how often you weigh yourself, in order for the comparisons to be meaningful, it's important that the circumstances be as uniform as possible. First thing in the morning with no clothes and an empty bladder, is usually the easiest. Even then, be aware that water retention can vary from day-to-day if your salt and/or water intake varies (water weighs 8.3lbs/gallon).
My own... personal... nightmare
It may seem innocent, but a simple bathroom scale can be one of the most terrifying objects imaginable. Hyperbole aside, it was certainly an emotional experience for me getting on a scale for the first time in several years. It was made even more so by the need to hunt down a scale that would accommodate my (quarter-)tonnage. But in the end, it had to be done and I'm better for the experience and knowledge.
You can do it!