Losing weight is like a squiggly line, not a straight line. Some days you might eat a little more, some days you might eat a little less. Some days you might expend more calories by being more active, some times a little less. It will all balance out. What is more concerning is that by being so rigid in your diet, you are setting yourself up to obsessive behaviors which results in an unhealthy behavior with food. Sure, you calorie intake isn't "eating disorder" level. But take it from someone who has been there and now struggles every day not to totally obsess over calorie intake and calorie burn. If you are having success watching calories, then good for you! But please realize that even if you had went over your calorie intake goal, one day is not going to cause you to ruin your diet and one 100 calorie pack too many is not going to make you gain weight. Personally, I think that 100 calorie packs are not the best choice for your health. Low calories do not equal healthy food. You'd be better off having something you really want and having it in moderation. For the 200 calories you consumed, you could have had almost a whole candy bar. This isn't healthier per se, but if it satisfies your craving and doesn't leave you craving more, than it was better for you and your relationship with food.