Eating at night will not make you overweight.  

Eating dinner

A lot of experts recommend against eating past 6 p.m. because they mistakenly believe that it might make you more likely to gain weight.  This type of advice might seem to make sense because we are less active at night, but it is also misleading. Weight gain is more about what and how much you eat and not back when you eat it.  The belief that separates fact from fiction when it comes to late-night eating and weight gain.

The conventional wisdom today is that a calorie is a calorie, yet in practice, this is not the truth.  Sugar and foods that processed are not equal in nutrition to lower processed foods.  Weight gain is eating more calories than you burn, but there is a component of what you eat as well.  For most of us, we eat too much and too poorly (quality and quantity).  Sure, there is also a part of obesity tied to exertion, but a slim waistline is more from the kitchen than the gym.  

No matter, I would still recommend that you watch what you eat at night.  Nighttime eating is tied to poor sleep and reflux disease (heartburn).  Reflux is a damn good reason to be cautious about eating at night. 

The bottom line:  Nighttime eating is not the cause of your weight gain.  Kill this myth once and for all.  Physiologically, calories do not magically count for more at night, so you will not gain weight due to eating at night.  Recommend choosing foods wisely and watching the portion sizes more than the timing of meals.