The calculators at IIFYM.com
are pretty accurate.
The reason you are confused is that you are doing it wrong.
Your BMR is how many calories you burn at rest; while sleeping.
To figure out how many calories you need to eat to lose weight, you need to go off of your adjusted BMR which is your TDEE.
TDEE = BMR + Calories burned through daily activity
I use the TDEE calculator and it matches up with my bodybugg pretty accurately..
Subtract your 500-700 calories off of your TDEE and you will be golden.