Weight loss is not matching deficit

[SunsetRunner]

The past three weeks have yielded only 1lb of weight loss, although according to my cumulative calorie deficit I should have expected a 2.4lb loss.  What could be the reason for this discrepancy?  Is it wishful thinking to hope that I have gained muscle?

Background information:

I am a 28 year old female, 5'7", 144lb and 21-23% body fat.  I have been logging my food intake religiously, sometimes even over estimating what I eat to be on the safe side.  I've been doing 1 hour of moderate to vigorous cardio activity 6/7 days of the week (this is new to my body, I will admit that prior to 2 months ago I was relatively inactive).  I have also incorporated regular strength training and yoga into my daily routine.  

[GershonSurge]

@SunsetRunner,

It probably means your device is overestimating calories burned by 233 calories/day. This is normal for the devices with heart rate monitors. 

[Dominique · Accepted solution]

Your calculated BMR (as per the Mifflin St Jeor equation) would be 1416. Your calculated TDEE with the 2nd highest activity level (out of 5), which may match your described activity, depending on how active you are outside your 1 hour moderate-vigorous cardio session, would be 2442. The "missing" loss of 1.4 lb would be 233 cal. per day, as already noted by @GershonSurge. If your Fitbit says you’re burning 2600-2700 in average, it could be be overestimating your real expenditure by that amount. I reported the discrepancy I observed between Surge and Charge 2 over a 4-month period: it amounted to about 100 calories per day in average. And my first Fitbit (One) reported even lower calories than either of these, which is in line with what @GershonSurge observed.