At the extremes the effect on the weight is very predictable. Keeping everything else the same when you reduce your calorie intake to zero, you will reduce weight. Or increase your intake to 3 x recommended daily values and your weight will go up.

Everything in between is affected by cumulative margin of error. There are inaccuracies when calories are calculated, then variations of portions, variations of individual metabolism and compositions of gut bacteria. If you throw the "not all calories are equal" in the mix you get even more variations.