I decided to join FD to start tracking my calories. Actually, I started out at Everyday Health dot com and then moved to FD because the nutrition tracking was better. As with any such website I wondered how accurate the results would be with my body type. I understand that the formulas used as well as the data I enter is estimates and that there is no way to create a perfect system that works flawlessly for all. Having said that, I suspect some people are getting better accuracy than me and some probably less. I'm not really hardcore about measuring everything I eat. I estimate portions most of the time. I also doubt that my activity entries are and better than close most of the time, since I do not use a heart monitor for exercise. So, since I'm a bit of a spreadsheet junkie, I decided to enter my data from FD into a spreadsheet so I could do some of my own analysis.
I weigh myself every morning, usually at the same time but sometimes it's a little later than others. My spreadsheet gives me a daily weight projection based on the previous days weight, calorie intake and burn. Using that metric over time I projected weight with a linear trend line (blue lines) to predict where I should be at on the goal date. It has me beating my goal date by nearly 3 weeks, which ain't gonna happen. I also created a line for the goal (green line) itself for comparison purposes, as well as actual weight (red line with a pink dotted trend) loss progress.
My actual weight loss results reflect about 4.5 lbs variance over the projected weight loss. That is to say, I'm going well beyond what the FD calorie restriction suggests (which is 860 per day, or 1.75 lbs per week). However, what I'm doing does still have me slightly ahead of my goal pace. The variance there is very slight.
The following graph shows my progress against my goal and a projected loss based on actual tracking.
I attribute the variance for me to my estimates on intake and burn. All in all, I'd say the formulas used here are going to yield fairly accurate results for most people, keeping in mind the degree of accuracy we each use in measuring our daily calorie intake and burn.
I'd say the results for those using estimates to be better if you use conservative numbers.