BMR and calorie intake

ethelapple

So, here's my question....when I calculate my BMR, I come up with about 2,620 calories used per day just to keep me alive. I have my calorie intake set at 1650. I don't necessarily eat back exercise calories, only if I am hungry for them. But let's say for example that I eat 1400 calories one day -- does that mean I have a deficit for that day of about 1200 calories? (my BMR minus what I consumed)???
And if a lb. is about 3600 calories, I should be losing a lb. every three days merely by eating the 1400 calories alone.....but somehow, it doesn't seem to work like that. Maybe I am simplifying it too much? Maybe I'm way off? A little clarification here would be good.