Weight Loss Doesn't Match My Deficit

Last week I created enough of a deficit to lose 1lb but showed no loss on the scale. This week on the third day of dropping my calories down to just over 1200 calories I lost 2.5lbs. The deficit I had at that point was only about 2400 cals. What gives?

I'm glad about the weight loss but tracking my deficit is one way that I thought I could make sure I was hitting my weight loss goals for the week and this is really just throwing me off

As much as we'd all like it to be that simple, calorie counting is not exact math. For starters, it's pretty much impossible to know EXACTLY how many calories you burn one day, and EXACTLY how many you eat. The tools provide some of the best approximation out there, but you never know for sure, without a doubt, how much calories you eat or burn. (ex: one grape can have more sugar than another, the number you'll see when you search is an approximation. Same for prepackaged food).

On top of that, you also have to factor in water weight and the way your body burns energy. You might be working hard and your body is retaining water in your muscles to repair them, or you might have had more sodium one day and the next, you flushes most of it out. And there are many many more factors.

Ex: I was 205.8 yesterday, and I was 202.8 this morning. Now, I don't think I had 3x3500 calories deficit. I was probably just retaining water.

I agree with emilie_f - it just isn't a perfect system. I followed the 500 calorie deficit religiously all summer - some weeks I lost 2 pounds a week, and other weeks I lost half a pound. Diet soda made me gain, food pyramid made me lose. Who knows - it does require patience - i am on a plateau right now, and have decided to eat to maintain and start up again in a month or so, rather than make myself crazy.

I suspect your weight loss was maybe the deficit you created over the 2 week period - our bodies don't always follow the same time frame we are looking at. If you are losing- awesome!

water weight, food still in your system... it could have been anything.  It'll even out in the long run.

Your deficit is only as accurate as the information you use to calculate it.  If you are calculating your deficit based on a formula that represents averages for all individuals with your characteristics, it is likely you are introducing a bit of error.  Second, error is introduced in the process of measuring the food that you eat.  Third, accurate measurements of body fat are difficult to come by (we usually use body weight as a proxy), resulting in more error.  Lastly, 3500 kcal/pound is an average figure for burning fat and is therefore yet another source of error.

Certainly you should try to accept that your estimates are just estimates and expect a good deal of variance.  But, you can also try to improve your estimates if you want.

Why not try to calculate your deficit and daily burn based on your own data?  If you have the proper data, try this: pick a 30+ day period (you could do a shorter period, but it would be less accurate) and calculate how much weight you lost.  For the sake of example, I'll use a 30 day period and a 4 pound loss.  A loss of 4 pounds corresponds to 4*3500=14000 kcal deficit; divide that deficit by 30 days and you get an average daily deficit of 466.6.  If you want to know what your average daily burn is, you can estimate that by adding your average caloric intake for the same time period (I'll use 1400) to the deficit you already calculated: 1400+466.6=1866.6  For many people (myself included) these figures are more accurate than the averages provided by BMR/RMR calculators.