The problem with that old weight-loss formula, researcher's now say, is that it doesn't take into account what might be happening when you're not exercising: the calories you would have burned anyway, the calories you'll add from overeating after overtraining, and the ones you won't burn the next day because you're too sore to move.
The old weight-loss math assumed that your body was like a block of marble and that by systematically chiseling away at it with exercise you could gradually get rid of the undesirable stuff and end up with perfect abs. But your body's not a block of marble, it's in a constant tug-of-war between consuming and burning calories, whether you're eating, sleeping, reading, or watching TV. So the calculus for getting rid of that pound is far more complex than just subtracting the "calories burned" number from your weekly goal at the end of each workout.
The bottom line: Consistant dynamic workouts and understanding your daily calories, portions, and meal frequencies.
Lifestyle Fitness Coach